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Contents xi 1IntroductiontotheEcologyEpidemiologyandEvolutionofParasitisminDaphnia 1 11Foreword 1 12SettingtheStage ID: 392482

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Contents Acknowledgments xi 1IntroductiontotheEcology,Epidemiology,andEvolutionofParasitisminDaphnia 1 1.1Foreword ............................................... 1 1.2SettingtheStage ........................................... 1 1.3DeningParasites .......................................... 2 1.4Host–ParasiteInteractions ..................................... 2 1.5OutlineofThisBook ........................................ 3 1.6UpdatesandCorrections ...................................... 4 2IntroductiontoDaphniaBiology 5 2.1Introduction ............................................. 5 2.2Physiology,Metabolism,andImmunity ............................. 7 2.3LifeCycleandDevelopment .................................... 10 2.4Habitat ................................................ 14 2.5BehavioralEcology ......................................... 15 2.6EvolutionaryGenetics ....................................... 17 2.7PopulationDynamics ........................................ 18 3SomeParasitesofDaphnia 19 3.1Introduction ............................................. 19 3.2Bacteria ................................................ 19 3.2.1PasteuriaramosaMetchniko 1888 ............................ 21 3.2.2SpirobacilluscienkowskiiMetchniko 1889 ........................ 22 3.2.3WhiteFatCellDisease ................................... 23 3.3Fungi ................................................. 24 3.3.1Metschnikowiabicuspidata(Metschnikov)Kamenski .................. 24 3.4Microsporidia ............................................ 25 3.4.1FlabelliformamagnivoraLarssonetal.1998 ........................ 26 3.4.2OctosporeabayeriJirovec1936 ............................... 26 3.4.3Glugoidesintestinalis( Chatton1907 )Larssonetal.1996 ................ 27 3.4.4OrdosporacolligataLarssonetal.1997 .......................... 29 3.5UnknownClassication ...................................... 30 3.5.1CaulleryamesniliChatton1907 ............................... 30 xiiAcknowledgments onit.Sincethen,mylabhasdevelopedculturingmethodsformorethan10speciesofparasites.ThisworkwiththeDaphniaparasiteshasab-sorbedmyattentionsincethen,andtogetherwithmyresearchgroup,IhavespentmanyexcitinghoursinthelaboratoryandintheeldndingoutmoreaboutDaphniaparasites,andaboutparasitesingeneral.TheDaphnia– microparasite systemhasprovedtobeapowerfulmodelformanyquestionsinbasic epidemiology ,ecology,and evolution .Theupcominggenomedatawillextendthisintothe“ NarrowRoadsofGeneLand “(thetitleofBillHamilton'ssecondbookwithmanypartsontheevolutionofhost–parasiteinteractions,2001)andwillhopefullyopenupapluralisticapproachtounderstandinghost–parasite coevolution .ThisbookwouldnothavebeenpossiblewithoutthecollaborationofthemarvelouspeopleworkingwithmeinOxford,Silwood,Basel,andFribourg,andalsocollaboratorsfromaroundtheworldwhosharedmyenthusiasmforhost–parasitein-teractions.Iwanttothankthepeopleinandaroundmygroup(inroughlychronologicalor-der):ValentinoLee,KatrinaMangin,HeideStir-nadel,SvenKrackow,JudyWearing-Wilde(Ox-ford),DermotMcKee(SilwoodPark),ChristineZschokke-Rohringer,Hans-JochaimCarius,TomLittle,DanielFels,MarcCapaul,MyriamRiek,PatrickMucklow,PiaSalathé,KatjaPulkkinen(Basel),ChristophHaag,DominikRefardt,DitaVizoso,OlgaSakwinska(BaselandFribourg),Lu-siaSygnarski,SandraLass,MarcZbinden,KnutHelgeJensen,Ra aelAye,FlorianAltermatt,HollyGanz(FribourgandBasel),andThomasZum-brunn(Basel).SpecialthankstoJürgenHottinger,whobecameovertheyearsnotonlyaclosefriendbutalsotheirreplaceablecenterofthegroup.Nu-merouscollaborators,manyofwhomaretheoreti-cians,helpedopenmyeyeswhenIwasblindedbythebeautyofDaphniasymbionts:SebastianBonhoe er,MarcLipsitch,MartinNowak,Wolf-gangWeisser,RichardLenski,BillHamilton,PaulRainey,MitjaScholz,MartinEmbley,JanneBengts-son,LizCanning,SteveStearns,IlmariPajunen,RolandRegoes,RonnyLarsson,KerstinBittner,EllenDecaestecker,andPaulSchmid-Hempel.Flo-rianAltermatt,HollyGanz,SandraLass,DominikRefardt,MarcZbindenandThomasZumbrunnreadmostofthebookinearlierdraftsandhelpedmetopolishstyleandcontent.DitaVizosopro-ducedseveralgurestoillustrateimportantas-pectsoflifecyclesandtransmission.DitaVizosoandFridaBen-Amiarethankedforcontributingphotographs.IthankmysonGlebforhelpwithproducingsomeofthegures.SuzanneZweizigimprovedthestyleandreadabilityofthelanguagethroughoutthebook.RitaGunasekerahelpedmewiththeformattingofthevariousles.JoMcEn-tyreandLauraDeanwereofgreathelpinallas-pectsofpublishingthisbook.Thankstotheirwork,thebookcanbemadeavailabletoawideaudienceviatheInternet.Finally,Iwanttothankmyfriendsandfamilyfortheirsupportandtheencourage-menttowritethisbook.November2005DieterEbert 2Ecology,Epidemiology,andEvolutionofParasitisminDaphnia researchhasaddressedanumberofevolutionaryquestions,resultinginawell-roundedpictureoftheevolutionaryecologyofthegenus.Foralongtime,researchfocusedon predators asthemainenemiesofDaphniaintheirnatu-ral habitat .Predatorysh,phantommidgelarvae,andwaterboatmenwereamongthekeyculpritsandreceivedalotofattention,inparticularafter predator-induceddefenses weredescribed.ThisinterestinpredatorsexistedinsharpcontrasttothelackofattentionpaidtoanotherclassofDaphnia'snaturalenemies, parasites and epibionts .DespitenumeroustaxonomicstudiesontheepibiontsandparasitesofDaphnia,therewaslessthanahand-fulofecologicalstudiesonthemupuntilabout15yearsago.Thegrowingawarenessthatparasitesareubiquitousandmayplayanimportantroleinmostnaturalecosystemshaschangedthis,astheincreasingnumberofpublicationsaboutDaphniaparasitesandepibiontsconrms( Figure1.1 ). 1.3 DeningParasitesAlthough parasites havetraditionallybeendenedbyacombinationofconceptualandtaxonomicfea-tures,Iuseanentirelyconceptualdenitionhere.Iconsideraparasitetobeanysmallorganism(in-cludingviruses)thatlivesincloseassociationwithahostorganismandforwhichitseemsreasonabletoassumethatthehostcarriessomecost.Thesecostsmaybeclearlyvisible,intheformofreducedfecundityorsurvival,butmayinsomecasesbesubtle.Forexample,reducedsexualattractiveness(leadingtoreducedmatingsuccess)orreducedcompetitiveabilitymaynotbeveryvisible.Ide-voteanentirechaptertodiscussingthe tness costscausedbyparasites.Thisconceptualdenitionofaparasiteincludesmembersofvarioustaxa,suchasviruses,bacteria,fungi,andprotozoa,butalsoincludesfunctionalcategories(nottaxonomicallydened),suchas pathogens and helminths .Incon-trasttotypical predators ,parasitesdonotalwayskilltheirhosts,andiftheydo,itmaytakeaconsid-erableamountoftime,duringwhichtheparasitemaybetransmittedtootherhosts,andthehostremainsinthecommunitycompetingwithotherorganismsforspace,food,andmatingpartners.Intheliteratureon Cladocera andmorespeci-callyonDaphnia,parasitesareoftendistinguishedfromepibionts.Whereastheformerareusually endoparasites ,i.e.,locatedwithinthebodyofthehost,thelatterarelocatedonthebodysurfaceandmaythereforebelabeledasectoparasites.Inthemainpartofthisbook,Iconcentrateonendopara-sitesandexcludeepibionts.However,thisisnottosaythat epibionts arenotparasitesorarenotim-portant.Infact,Ibelievethatmostepibiontsfulllthedenitionofparasitesusedhere,becausetheyareoftencloselyassociatedwiththeirhostsandcauseharmtotheirhosts.Thisharmmaynotbedi-rectlyvisible,buttherearecertainlyincreasedcostsforswimming,whichmayhaveconsequencesforother tness components,suchasfecundity,sur-vival,competition,andmatending( Threlkeldetal.1993 ).Ithasalsobeensuggestedthatepibion-ticlterfeederscompetewiththeirhostsforfood( KankaalaandEloranta1987 ).Ontheotherhand,ithasbeensuggestedthatundercertaincondi-tions,highloadsofalgalepibiontsmayprovideadditionalfoodforthehostandthusresultinanetbenet( Barea-Arcoetal.2001 ).However,thisformofafoodsupplementationiscertainlynotthetypicale ectofepibionts.Idonotincludeepibiontsinthisbook,becauseIfeelthatthereislessneedtodiscussthe epidemiol-ogy ofthisfunctionalgroupthanforendoparasites.However,IwillrefertothemwheneveritmightfurtherourunderstandingofDaphnia–parasitein-teractions. 1.4 Host–ParasiteInteractions Parasites maybedirectlyorindirectlyinvolvedintheecologyand evolution ofabroadrangeofphenomena:host populationdynamics andextinc-tions,maintenanceofgeneticdiversity,sexual se-lection ,evolutionofgeneticsystems,andevolutionofsexualrecombination,tonamejustafew.Cer-tainly,parasitespossessfeaturesthatmakethemveryattractiveasexplanatoryfactorsintheevolu-tionandecologyoftheirhosts.Thesefeaturesin-cludetheirhigh abundance innearlyeveryecosys-tem,theirtypicallynarrowhostrange(comparedwithtypical predators ),theiradversee ectsontheirhosts(e.g.,reducedfecundityandsurvival),and densitydependence during horizontaltrans-mission ( Anderson1979, 1993 ; AndersonandMay1978 ; MayandAnderson1979 ; Price1980 ). 4Ecology,Epidemiology,andEvolutionofParasitisminDaphnia Chapters8 and 9 addressaspectsofparasitismatthe population level.Acentralchapterofthisbookis"Epidemiology."Itstwopartsdealwith transmis-sion processesandwiththeactualepidemiologyofDaphniaparasites.Chapter9introducestheimpor-tantquestionofwhetherparasitesregulatetheirhostpopulationsorevendrivethemtoextinction. Chapter10 introducesanumberofexperimentsthatonemaydowithDaphniaanditsparasiteswithintheframeworkofastudentcourseorforresearchpurposes.Thesesimpleexperimentsmaybeusedtoillustrateprinciplesofhost–parasitein-teractions.Experimentsaresuggestedattheindi-viduallevelaswellasatthepopulationlevel.From Chapter4 onward,Iendeachchapterbyposingopenquestionsandhighlightingmajorgapsinourknowledge.A Glossary providesdenitionsoftermsfromDaphniabiologyandparasitologyusedthroughoutthebook. 1.6 UpdatesandCorrectionsIwillmaintainaWebsiteonmyhomeinstitu-tion'sservertoreportupdatesandcorrecterrors.Ifyounderrors,disagreewithcertainstatements,orndthatIneglectedimportantinformation,Iwouldbehappytoreadyourcomments.Pleasesendmeanemail: dieter.ebert@unibas.ch 6IntroductiontoDaphniaBiology Figure2.1ThefunctionalanatomyofDaphnia.Thisdrawingshowsanadultfemalewithparthenogeneticembryosinher broodchamber .Forbetterillustration,the carapace isshownastransparent.Theanimalmeasuresabout2mmfromthetopofitsheadtothebaseofitstailspine.ModiedafterMatthes( rstpublishedonpage154inKükenthalandMatthes1944 )(withpermissionfromKästner:LehrbuchderspeziellenZoologie,Band1,Teil4,1993c ElsevierGmbH,SpektrumAkademischerVerlag,Heidelberg).ComparethisgurewithFigure2.2. 2.2Physiology,Metabolism,andImmunity9 Figure2.5Daphnialongispina.Adultfemalewiththreeeggsinthebroodchamber.ThisfemalewasisolatedfromarockpoolinsouthernFinlandclosetoTvärminne. Daphniahavetheextracellularrespiratoryproteinhemoglobin(Hb),amulti-subunit,multi-domainmacromolecule.ThereareatleastfourHbgenes.DaphniatendtodevelopmoreHbtoincreaseoxy-genuptakefromthewater.Inresponsetoenvi-ronmentalchanges(oxygenconcentration,temper-ature),theHbconcentrationvariesuptoabout20-fold.Oxy-hemoglobin,theformthatisloadedwithoxygen,isredandgivesthetransparentan-imalsareddishappearance( Figure2.7 ).Becausecertainparasitesalsocausethehemolymphtobe-comered,onecannoteasilydeterminethecauseoftheredcolorfromsightalone.However,lowoxygenusuallya ectsanentire population ,color-ingallanimalsreddish,whereasparasitesusuallyinfectonlyaportionofthepopulation.Daphniahavetheusualosmoregulatoryprob-lemsoffreshwateranimals,i.e.,toomuchwaterandtoofewsolutes.Theyareabletoabsorbionswithchloride-absorbingglands.The shellgland ( maxillarygland ; Figure2.1 )mayhavearoleinexcretionand/orosmoregulation. Figure2.6GutofDaphniamagna.Gutdissectedfromafemale.Ontheleft,thepairedintestinalcecacanbeseen.Thegutendsattherightside.Theesophaguscannotbeseeninthispreparation.Thedarkmaterialispartiallydigestedgutcontent. Figure2.7TwoDaphniamagnawithcontrastinghemolymphcolorduetohaemoglobin(Hb).ThesetwoadultfemalesweretakenfromtwoadjacentrockpoolpopulationsinsouthernFinlandatatimewhenoneofthepoolswaslowinoxygen(becauseofoverfertilizationfrombirddroppings).Intheleftfemale,lowoxygentrig-geredtheproductionofHb,whichgivesthehemolymphareddishcolor.Thefemaleontherightwastakenfromapoolwithclearwaterandapparentlynormaloxygenlevels.Thesizedi erenceoftheanimalsisattributabletothearbitrarychoiceofspecimens.Bothfemalesarecarryingembryosintheirbroodchambers. Thenervoussystemischaracterizedbythecere-bralganglion,whichislocatedclosetothegutandneartheeye.JuvenileandadultDaphniahaveonelargecompoundeye,whereasembryosshowtwobrownisheyespotsthatfuseduringthelastpartofthedevelopment.Thecompoundeyehelpstoori-enttheanimalwhileswimming.Asmallstructure 10IntroductiontoDaphniaBiology calledanaupliareyeislocatedbetweenthemouthandthecompoundeyeontopofthecerebralgan-glion.Manyinvertebrates,including crustaceans ,haveawell-developedinnateimmunesystemthatin-cludesmelanizationbyactivationoftheprophe-noloxidase(proPO)activatingsystem,aclottingprocess,phagocytosis,encapsulationofforeignmaterial,antimicrobialaction,andcellagglutina-tion( Söderhall1999 ).Ofthesemechanisms,onlythe proPOsystem ( MucklowandEbert2003 )andphagocytosis( Metchniko 1884 )havebeeniden-tiedinDaphnia,althoughthereisnoreasontodoubtthattheothermechanismsworkaswell.TheproPOsystemisnotonlyadefensesystemagainstparasitesbutisalsoinvolvedinwoundhealingofthecuticle( Figure2.8 ).Theenzymeinvolvedin melanin formation,PO,hasbeendetectedinthebloodofmanyarthropods,includingD.magna.Melaninisabrownpigmentthatisalsousedfor carapace pigmentationinsomeDaphnia,particu-larlyDaphniainthehighArctic,wherethedarkpigmentprotectsthemfromuninterruptedsolarradiation(repairofUVdamageisonlypossibleinthedark).Acquiredimmunityisthoughttobeabsentininvertebrates;however, transmission ofstrain-specicimmunityfrommotherstoo springhasrecentlybeensuggestedforD.magna( Littleetal.2003 ). 2.3 LifeCycleandDevelopmentThelifecycleofDaphniaduringthegrowthseasonischaracterizedbyitsasexualmodeofreproduc-tion( apomixis )( Figure2.9 ).Afemaleproducesaclutchofparthenogenetic(amictic)eggsaftereveryadultmolt(iffeedingconditionspermit). Figures2.3 to 2.5 showfemaleswithparthenogeneticeggs.Theeggsareplacedinthe broodchamber ,whichislocateddorsallybeneaththe carapace andwhichisclosedbythe abdominalprocesses ( Figures2.1 and 2.10 ).Developmentofeggsisdirect(imme-diate).At20oC,theembryoshatchfromtheeggsafterabout1daybutremaininthebroodchamberforfurtherdevelopment( Figure2.11 ).Afterabout3daysinthebroodchamber,theyoungDaphniaarereleasedbythemotherthroughventralexionofthepost-abdomen.ThenewbornlookmoreorlessliketheadultDaphnia,exceptthatthebrood Figure2.8WoundhealinginDaphniamagna.Aninjuryinthecarapacehealswithinafewhourstodays.Woundhealinginvolvesamelanizationreactionthatstainsthewounddark.Hereaneedlewasusedtoinjurethecara-pace.Thesquaredpatterninthebackgroundshowstheepidermalcellstructure. chamberisnotyetdeveloped( Figure2.12 ).Inmostspecies,ajuvenileDaphniapassesthroughfourtosixjuvenile instars beforeitbecomes primipare ,i.e.,produceseggsforthersttime.Theageatwhichthersteggsaredepositedintothebroodchamberisaround5-10daysat20oC,butthismaytakelongerunderpoorfeedingconditions.Anadultfemalemayproduceaclutchofeggsev-ery3to4daysuntilherdeath.Inthelaboratory,femalesmayliveformorethan2months,withahigheragebeingreachedunderpoorerfeedingconditions.Clutchsizesvaryamongspecies,from1to2eggsinsmallspeciessuchasD.cucullata( Figure2.4 )tomorethan100inlargespeciessuchasD.magna( Figure2.3 ).AlthoughinatypicalgrowthseasonDaphniaproducediploid(2N)eggsthatdevelopdirectlyandwithoutarestingphase,adi erenttypeofeggisproducedforresting( Figure2.9 ).These rest-ingeggs areencapsulatedinaprotective,saddle-likestructurecalledan ephippium ( Figures2.13 and 2.14 ),whichisusuallystronglymelanizedandcontains2largeeggs,1fromeachovary.Itisnotuncommon,however,tond ephippia withonly1egg,ornoneatall.Theephippiumiscasto atthenextmolt.Inmostcases,theseeggsareproducedsexually,butobligateparthenogeneticDaphnia,whicharetypicallyfoundinthenorth- 12IntroductiontoDaphniaBiology Figure2.10EgglayingbyDaphniamagna.Thisseriesofpictures,takenwithina15-minutetimespan,showstheprocessofplacingeggsintothebroodchamber.Theeggsareinitiallysausageshapedbutquicklyresumeanearlysphericalshape.Theovariesshrinkduringtheprocessofegglaying.Inthetoppictures,theyareclearlyvisibleasadark,thicklineparalleltotheintestine. Chapter3SomeParasitesofDaphnia Inthischapter,IgiveabriefintroductiontosomeendoparasitespeciesofDaphnia.Threebacteria,onefungus,fourmicrosporidia,andoneparasiteofunknowntaxonomicclassicationaredescribedwithaccompanyingphotographs.Ifocusonthoseparasitesthatarementionedfrequentlyinthisbook. 3.1 IntroductionThisbookismainlyconcernedwiththeecology, epidemiology ,and evolution of parasites .Itdoesnotgointodetailaboutthenaturalhistoryandtax-onomyofparasitespecies.Asecondbookwilldealwiththeseaspects.However,becauseitisusefultohavesomebasicknowledgeabouttheparasitesthatarefrequentlymentionedinthisbook,Igivehereabriefintroductiontothem.Moredetailswillbefoundintheupcomingbook,whichincludeschaptersonallknownDaphniaparasites. Table3.1 givesanoverviewaboutallparasitesofDaphniamentionedinthisbook.TheparasitesdescribedinthischapterarebynomeansmoreimportantthananyotherparasitesofDaphnia,buttheyarethosethathappentobethemoststudied,partlybecausetheyhavebeenfoundtobeatleastlocallyabundant.ParasitesofD.magnaarepredominantbecauseparasitesofthiswell-investigatedandlargestEuropeanDaph-niaspeciesarebestknown.MostofmyownworkonparasiteshasusedD.magnaasahost.Also,par-asitesforwhoseentirelifecyclecanbecompletedunderlaboratoryconditionsweremoreintensivelystudiedthanthenumerousspeciesthatwedonotcurrentlyknowhowtopropagate.Despitethisbiasinrepresentation,however,thespeciesintroducedinthischaptergiveagoodimpressionofthediver-sityofparasitesknowntoinfectthegenusDaphnia.Wehaveagoodknowledgeofthetaxonomicpo-sitionofonlyafewendoparasitesofDaphnia.Forsomespecies,wedonotevenknowtheapprox-imateposition,e.g.,Caulleryamesnili;therefore,Icannotuseastricttaxon-basedlistingofthepara-sitespecies.InsteadIprovideinformationonotheraspectsoftheirbiology,whichallowsustocatego-rizethemintogroupssothattheycanbeeasilyfound.WhenDNAsequencedataareavailableformorespecies,taxonomicpositionwillbeeasiertodene( Ebertetal.1996 ; Refardtetal.2002 ). 3.2 BacteriaSixspeciesofbacteriahavebeendescribedparasitizingDaphnia.Fouroftheminfectthehemolymph,whereastwoareintracellularinfec-tionsofthefatcellsandtheeggs,respectively.Bacterialinfectionsaregenerallyharmfultotheirhosts,drasticallyreducinghostreproductivesuc-cess.BacteriahavebeenobservedtoinfectDaphniaei-therasendoparasitesor epibionts .However,onlythetaxonomyforPasteuriaramosahasbeenworkedoutandpublishedthusfar( Ebertetal.1996 ).The 20SomeParasitesofDaphnia Parasite(Taxon)RecordedhostsInfectedtissueorsiteofinfectionTransmission Pasteuriaramosa(Bacteria)D.magna,D.pulex,D.longispina,otherCladoceraBlood,extracellularHorizontal,fromdeadhostWhiteFatCellDisease(Bacteria)D.magna,D.pulex,D.longispinaFatbody,intracellularHorizontal,fromdeadhostSpirobacilluscienkowskii(Bacteria)ManyDaphniaspeciesBlood,extracellularHorizontal,fromdeadhostAphanomycesdaphniae(Fungi)D.hyalina,D.pulexBodycavity,extracellularHorizontal,fromdeadhostMetschnikowiabicuspidata(Fungi)D.magna,D.pulex,D.longispinaBodycavity,extracellularHorizontal,fromdeadhostFlabelliformamagnivora(Microsporidia)D.magnaFatbody,ovaries,intracellularVerticalOctosporeabayeri(Microsporidia)D.magnaFatbody,ovaries,intracellularVerticalandhorizontal,fromdeadhostGurleyavavrai(Microsporidia)D.pulex,D.longispinaCarapace,intracellular?Glugoidesintestinalis(formerlyPleistophorai.)(Microsporidia)D.magna,D.pulexGutwall,intracellularHorizontal,fromlivinghostOrdosporacolligata(Microsporidia)D.magnaGutwall,intracellularHorizontal,fromlivinghostLarssoniaobtusa(=L.daphniae)(Microsporidia)D.magna,D.pulex,D.longispinaFatbody,intracellular?Pansporellaperplexa(Amoeba)D.magna,D.pulex,D.longispina,D.hyalina,D.obtusaGutwall,extracellularHorizontal,fromlivinghostCaulleryamesnili(unknown)D.pulex,D.longispina,D.magna,D.galeata,D.obtusa,DaphniahybridsGutwall,intracellularHorizontal,fromlivinghostEchinuriauncinata(Nematoda)D.pulex,D.magna,D.obtusa,otherCladoceraBodycavity,extracellularHorizontal,tosecondhostCysticercusmirabilis(Cestoda)D.magnaBodycavity,extracellularHorizontal,tosecondhost(?) Table3.1Listofparasitesmentionedinthisbook. 3.2Bacteria21 taxonomyofSpirobacilluscienkowskiiisinprepa-ration(M.Du y,personalcommunication).Theotherspeciesareeitherdescribedbytheirtypicalpathologyorarecollectivelyplacedintoagroupwithroughlysimilarcharacteristics.Mostspeciesdonotyethaveascienticname.Therecordedbacteriainfecteitherthehemolymphofthehostorareintracellular parasites .InfectionsofthehemolymphofDaph-niamaketheentirehostappearmilkish-white,brownish,pinkish,oryellowish.TheseinfectionscanbeseenthroughoutthebodyandhavebeenfoundinmanyDaphniaspecies.HereIintroducetwoofthesespecies:P.ramosaandS.cienkowskii.Incontrast,intracellularparasiticbacteriainfecteithercellsofspecichosttissuesoreggsofthehostwhiletheyareinthebroodpouch.HereIgiveashortdescriptionofalittle-knownbacteriumknownbythenameofWhiteFatCellDisease.Itscategorizationintotwogroupsofparasiticbacteriaisnotataxonomicclassicationbutafunctionalgrouping. 3.2.1 PasteuriaramosaMetchniko 1888P.ramosaisaGram-positivebacteriumbelongingtoadistinctcladewithinthefamilyoftheAlicy-clobacillaceae( Ebertetal.1996 ; Andersonetal.1999 ; Prestonetal.2003 ).Otherendospore-formingbac-teria,suchasBacillusandClostridium,arecloselyrelatedtoit.P.ramosaismostfrequentlyfoundtoinfectD.magna,butitalsoinfectsD.pulexandD.longispina.Itshowsahighdegreeofclone specicity withinspecies( Cariusetal.2001 ).Afewother Cladocera havebeendescribedashosts,butitisnotclearwhetherthe parasite wasindeedP.ramosa.P.ramosawasrecordedinEuropeandNorthAmerica.P.ramosainfectsthehemolymphandisex-tracellular( Figure3.1 )( Metchniko 1888 ).In-fectedhostsstopreproduction,growlarge,andthebodybecomesdarkishandnontransparentinlight.“Squash”preparationsreveallargenumbersoflarge,nearlysphericalspores(about5-mdi-ameter)orgrapeseed-shapedpre-sporesinthehemolymph( Figure3.2 ).Thisbacteriumcauseschronicinfections.In-fectedhostsaretotallycastrated,i.e.,theystopre-producingabout5to15daysafterinfectiontakes Figure3.1D.magnawith(right)andwithout(left)P.ramosainfection.Theparasitecanbeseenasadarkcloudymassllingtheentirebody.Thebroodpouchoftheinfectedfemaleisempty,whereasthehealthyfemalecarriesaclutchofeggs.Thisphotographwastakenwiththelightshiningfrombelow.Theinfectedhostislargerthanthehealthyfemale,whichistypicalforP.ramosainfections. Figure3.2DevelopmentalstagesofP.ramosa.Inthenalstageofsporedevelopment,thehostislledwiththeroundsporesthatserveastransmissionstages.Thesesporesarelong-lasting.Inhostsintheterminalstageofaninfection,oneoftenobservesafewcauliowerstages,suggestingthatsomesporesgerminatetostartanothergrowthcycle.ThecauliowerstageistherststageofP.ramosathatisclearlyvisibleafteraninfection. 3.2Bacteria23 Figure3.4D.magnawithWFCD.Thesameanimalisshownunderthreedi erentlightconditions,withlightcomingfromthetop(left),fromthebottom(right),andfromthetopandbottom(center).Notethattheinfectedfatcellsbecomelessvisiblewithlightshiningthroughtheanimal. Figure3.5WFCDinD.longispina.D.longispinafromanaturalrockpoolpopulationinsouthernFinland. Metchniko (1889) describedthelengthofthelifecycleofthebacteriumasabout5days.Thelifecycleincludesseveralmorphologicalforms,in-cludingovals,rods,spirillae,laments,androundspores.Hostscollectedfromnatural populations intheterminalstage(redcolorstage)surviveonly1-3daysunderlaboratoryconditionsandusuallycarrynoeggs( Du yetal.2005 ). Transmission isstrictlyhorizontal. Prevalence canreach10to15%forshorttimeperiods( Du yetal.2005 ). 3.2.3 WhiteFatCellDiseaseWFCDiscausedbyasmallcoccoid pathogen ,mostlikelyabacterium.Infectionswiththisbac-teriumhavebeenrecordedinD.magna,D.pulex,andD.longispina.ClonesofD.magnahavebeenfoundtodi erintheirsusceptibilitytoWFCD( De-caesteckeretal.2003 ).ThediseasehasbeenfoundonlyinWesternandNorthernEuropethusfar.ThecausativeagentofWFCDishardlyvisiblewithlightmicroscopy.Infectedhostshavebrightwhitefatcellswithaslightgreenishshinethat 24SomeParasitesofDaphnia isvisibleonlyinreectedlight( Figures3.4 and 3.5 ).Theinfectiondoesnotshowthefuzzyspreadthroughthebodycavitythatisseenwithother parasites infectingthefatcellsandovaries(e.g.,Octosporeabayeri).Usually,theinfectedtissueisclearlydistinguishablefromothertissues.WFCDisratherharmful.Itusuallykillsthehostwithin2weeks,oftenmuchmorequickly.Lessvir-ulentinfectionshavebeenobservedaswell.Fe-cunditydropsstronglywithdiseaseprogression,andinfectedhostshavestuntedgrowth. Transmission isstrictlyhorizontal.Transmissionstagesarereleasedfromdeadhosts.Thereseemstobenotransmissionfromlivinginfectedhostsandno verticaltransmission . 3.3 FungiSeveralspeciesoffungihavebeenobservedpara-sitizingDaphniaandother Cladocera .Taxonom-ically,theyarepoorlyunderstood.Theyvarystronglyintheirappearanceandtheire ectsontheirhosts.Fungalinfectionsaregenerallyharm-fultotheirhosts,drasticallyreducinghostrepro-ductivesuccessandsurvival.Somespeciesmaynotbeobligate parasites ,openingthepossibilitytoculturethemonanarti-cialmedium( Couch1935 ; Prowse1954 ; Whisler1960 ).Indeed,ithasbeenreportedthatthe en-doparasites Aphanomycesdaphniae,Metschnikowiabicuspidata,andthe epibiontic Amoebidiumpara-siticumcanbeculturedinvitro,whichopensuptremendouspossibilitiesforexperiments.Tomyknowledge,nootherparasitegroupcancurrentlybeculturedoutsideDaphnia.Host specicity seemstoberatherlowinfungiinfecting crustaceans .Frommyexperience,theparasiticfungiofDaphniaarethemostdiculttoworkwithandtoidentify.Ontheotherhand,par-asiticfungiseemtobethemostdevastatingdis-easesofDaphnia,oftenkillingthehostsquicklyordestroyingthebroods. 3.3.1 Metschnikowiabicuspidata(Metschnikov)KamenskiThisyeastisbetterknownbythenamesMonosporabicuspidataandMetschnikowiellabicuspidata.IthasbeenrecordedfromD.magna,D.pulex,andD. Figure3.6D.magnawithaninfectionofM.bicus-pidata.Thisfemalewasinfectedwithasuspensionofspores.Thehostisintheterminalstageofinfection.Theneedle-likeascosporesofM.bicuspidatalltheentirebodycavityofthehost. longispinaaswellasfromanumberofother crus-taceans .Itappears,however,thatunderthisnameacomplexofsimilarspecieshasbeendescribed.M.bicuspidataisanendoparasiticAscomycete(Endomycetales).Itproducesneedle-likeas-cospores,whichpenetratethegutwallsofitshostsandgerminateinthehemolymph( Green1974 ).Needle-like spores areusuallyupto45mlong,althoughtheycanbeupto90mlong( Green1974 ; CodreanuandCodreanu-Balcescu1981 ),andarevisiblethroughthetransparentbodyofthehosts( Figure3.6 ).Thefungusgrowsinsidethehostun-tiltheentirecavityislledwiththeneedle-likespores( Figure3.7 ).Sporesarefoundineverypartofthebodycavity,evenintheantennae.Hostsin 4.2OverviewofEpidemiologicalFieldStudies33 icallyfoundonlybetweenAprilandDecember.Theabundancepatternsofotherparasitespecieswerenottiedtoseasons,however,leadingGreentoconcludethatthedistributionofcertainpara-sitesisinuencedbytheseverityofwinterandspringtemperatures.Hedidnotdiscusstheroleofhostdensityasanexplanatoryfactor.Hedidob-serve,however,thatseveralparasitespecieshavenegativee ectsonhostsurvivalandfecundity. Brambilla(1983) studiedthemicrosporidiumThelohaniasp.inaD.pulex population overa3-yearperiodinasmall,apparentlyshlessvernalpoolinMichigan,USA.Henotedthatparasiteprevalencevariedstrongly,from20%topeaksofnearly100%ofadultfemales.ParasiteswerepresentinMayandJuneinall3yearsandwererstseenwhen-everthehostdensityroseabove2-3animals/liter.Oneyear,however,theparasitesdisappearedinmid-summerdespitehighhostdensities,suggest-ingthathighdensityalonecannotexplainpara-sitespread.Infectionoffemaleswith ephippia wasneverobserved.Parasitizedanimalswereusuallylargerthanuninfectedhostsbuthadlowerfecun-dityandsurvival. YanandLarsson(1988) followedthedynamicsoftwoundescribedandverysimilarmicrosporid-ianparasitesofHolopediumgibberumina32-haCanadianshieldlake(maximumdepth,16m)fromApriltoOctober1985.Thelakehasseveralplank-tivorousshspecies.ParasitesappearedonlyinJulyandreachedaprevalenceof4%,whichtheymaintainedfortherestofthesummer.Thepara-sitesappearedwhenhostdensitywashighbutdidnotdeclinewhenhostdensitydecreased.Theau-thorsarguedthatelevatedsummertemperatureswerenotthecauseoftheseasonaloccurrenceoftheparasites.Theyfurtherrejectedtheideathatchangesinhost resistance inuencedtheabun-dancepatternoftheparasites.Theysuggest,in-stead,thattheinterplaybetweenhostandpar-asite populationdynamics mayhavecausedtheseasonalchangesinprevalenceandthatpredationbyplanktivorousshmayhavefurtherinuencedthesechanges,becauseinfectedhostsmaybe,theyspeculate,thepreferredtargetofvisuallyhuntingsh.Infectedhostshadalowerfecunditythanhealthyhostsandmayhavehadlowersurvival.Inclosing,theauthorsnotedthatinasurveyof15otherH.gibberumpopulationsinshieldlakes,3ad-ditionalpopulationswerefoundtobeparasitizedbymicrosporidians. Vidtmann(1993) studiedparasitismbythemicrosporidiumLarssoniadaphniae(latercalledLarssoniaobtusa( VidtmannandSokolova1994) )inaD.pulexpopulationinashallow,shless,eutrophicpondattheKaunasZoologicalGar-deninLithuania.Heobservedthatalthoughmi-crosporidianswerepresentonlyduringtimesofhighhostdensity,theywerenonethelessoftenab-sentduringperiodsofhighhostdensityaswell.Prevalenceamongadultfemalespeakedinsum-meratamaximumof52%,buttheaveragepreva-lence(allageclasses)withinseasonsandacrossyearswasmuchlower:0.63%inspring,3.2%insummer,and2.4%infall.Prevalencewasgenerallylowerinjuvenilesandinmales.Over3years,themicrosporidianswereseenonlyfromlateMaytoearlyOctober.Becausethisperiodcloselyoverlapswiththepresenceofthehost,thisapparentsea-sonalitymayberelatedtotheseasonaloccurrenceofthehost.Nevertheless, Vidtmann(1993) spec-ulatedthatthedelayedonsetofL.daphniae epi-demics inMaywasaconsequenceoflowspringtemperatures. SchwartzandCameron(1993) studiedanunde-scribedtrematodeparasiteofD.obtusafromsevenseasonal,shlesspondsinsoutheasternTexas,USAover4years.Theyrecordedstrongwithin-season,between-year,andbetween-ponddynam-icsinthepresenceoftheparasite.Despiterecord-ingmaximum prevalences upto79%,theymoretypicallyfoundprevalencestobearoundafewpercents.Largeanimalsweremoreofteninfectedthansmallfemales.Hostfecunditywasonlyre-ducedininfectionswiththreeormoreparasitesperhost. Stirnadel(1994) and StirnadelandEbert(1997) studiedparasitesofD.magna,D.pulex,andD.longispinainthreeshlesspondsnearOxford,UKoveraperiodof1year(about10-12Daph-niagenerations,65samplesintotal).Sheassessedhostdensityandfecunditytogetherwithparasiteprevalence, richness ,diversity,andhost specicity .Overallparasiteprevalence(allspeciescombined)washighthroughouttheyear,averaging84.7%inadultD.magna,53.6%inD.pulex,and38.6%inD.longispina.Overall,31%ofD.magna,17%ofD.pulex,and11%ofD.longispnawereinfectedwithmorethanoneparasitespecies.Inallthree 4.3GeneralizationsaboutParasitisminNaturalPopulations35 4.2.2 ComparativeAnalyses Table4.2 givesonoverviewoverallcomparativeeldstudiesonCladoceranparasites. Green(1957) studied parasites and epibionts of Cladocera in67rockpoolpopulationsintheSkerryislandsofsouthernFinland.Thesepoolsweresmall(3-4minlengthandupto0.4mdeep)andshless. Parasiterichness declinedfromD.magnatoD.pulextoD.longispina,suggestingthatlargerDaphniaspeciesharbormoreparasites.Greenfoundthatsomeparasitespeciesloweredhostfecunditymorethanothers,andinonecase,heobservedthat ephippial femaleswereoverpar-asitized.Theauthorsuggestedthatcertainspeciesofepibiontscompetewitheachotherforspaceonthehostandthusexcludeeachotheratthepopu-lationlevel. Brunner(1996) (D.BrunerandD.Ebert,unpub-lishedobservations)investigatedsinglesamplesfrom43DaphniapopulationsinsouthernEngland,mainlywestofLondon.Waterbodiesrangedfromsmallpondsinparkstolargenaturalpondsandmedium-sizeddrinking-waterreservoirs.Mostofthesepondswereshless.Ninety-onepercentofthesepopulationsharboredatleastone endopara-sitic infection(mainlymicrosporidians).Theav-erageprevalencewasratherhigh.InthemorecommonDaphniaspecies,parasiteshadanav-erageprevalenceof43%(n=17)inD.magna,69.7%(n=17)inD.pulex,and43%(n=9)inD.longispina(allparasitespeciescombined).AmongtheD.magnapopulations,averageprevalencewas58.4%(standarderrorofthemean(SE),8.4)inpermanentponds,andonly23%(SE,6.4)ininter-mittentponds.Thisdi erencewas,however,mostlikelyattributabletothesmallersizeoftheinter-mittentponds.Asseeninotherstudies( StirnadelandEbert1997 ; Decaestecker2002 ),themostcom-monparasitesofD.magnaweremicrosporidiangutparasites. BengtssonandEbert(1998) conductedasimilarsurveywithonlyonesampleperpondinarockpool metapopulation alongtheSwedisheastcoastnearUppsala.Inthesepools,24of50(48%)D.pulexpopulationsand9of25(36%)D.longispinapopu-lationsinvestigatedharboredatleastoneparasitespecies.Acrossallponds,theaverage micropara-site prevalencewas15.5%forD.pulexand9.1%forD.longispina(about30%and25%whenonlypop-ulationswithatleastoneparasitespeciesarecon-sidered).Theinfectionsinthepoolswereprimar-ilyattributabletoasingle,virulentmicrosporid-iumspecies(possiblyLarssoniaobtusa( VidtmannandSokolova1994 )),whichreducedclutchsizeby98%. Ebertetal.(2001) studiedD.magnainthesamerockpool metapopulation insouthernFinlandasdid Green(1957) (seeaboveand Figure2.18 ).Be-causetheecologyofthismetapopulationiswellknown,itwaspossibletoaddressseveralaspectsofparasitedistributionacrosspopulationsinrela-tiontovariouspoolcharacteristics.Eightendopar-asitesandeightepibiontspecieswerefoundin137rockpoolpopulations.Thenumberofendopara-sitespeciesperpopulationincreasedwiththeageoftheDaphniapopulation.Typically,newerpop-ulationsfoundedintheyearthesurveywascon-ductedhadnoorfewparasitespecies,whereasolderpopulationshadincreasinglymore.Further-more,largerockpoolswithpresumablylargerandmorepermanentDaphniapopulationsweremorelikelytoharborparasitesthansmallerpools.ThemostprevalentparasiteintheFinnishrockpoolswasthemicrosporidiumOctosporeabayeri,whichoftenoccurredinaprevalenceof100%.ThisparasiteexclusivelyinfectsD.magnaandwasfoundinnearly50%ofallpopulations,withmuchhigherpercentagesinolderpopulations.Surpris-ingly, Green(1957) foundthisparasiteinonly8.3%ofD.magnapopulations. 4.3 GeneralizationsaboutParasitisminNaturalPopulations 4.3.1 WhatCanWeLearnfromPrevalenceEstimates?Prevalenceestimatesareacommonandconve-nientmeasureof parasiteabundance .Theyallowtheinvestigatortofollowchangesinparasiteabun-danceovertimeandprovideareasonablepictureofthedegreetowhichthehost population isin-fested.Prevalenceestimateshavesomelimitationsthathavetobetakenintoaccountwhendoingpar-asitologicalresearch.First,theyareusuallyunder-estimates,becauseparasitesareonlydetectableaf-tersignsofinfectionhavedeveloped.Infections 4.3GeneralizationsaboutParasitisminNaturalPopulations37 wererelativelymoreofteninfectedthanpartheno-geneticfemales.Theassociationbetweengenderandparasitismcertainlyneedsfurtherinvestiga-tion.Thee ectofparasitesonhostsurvivalhasbeentestedineldstudiesbybringingplanktonsam-plestothelaboratory,dividingtheindividualsintoinfectedanduninfectedgroups,andthenmoni-toringtheirsurvivalundercontrolledconditions.Foranumberofreasons,Iconsiderthisapproachtobeunsatisfactory.First,infectedandapparentlyuninfectedhostsmaydi erinsize,age,andexpe-rience.Becauseparasitesofteninuencegrowth,itisnotpossibletocorrectforthesedi erenceseasily.Second,theassessmentofinfectionstatusisoftendicult,withstrongvariationacrossinvestigatorsandamongdiseases.Forexample,certaininfec-tionsmayonlyberecognizableshortlybeforethedeathofthehost,whereasotherscanbedetectedafewdaysafterinfection.Thus,comparinginfectedanduninfectedanimalsfromeldsamplesdoesnotallowonetojudgethee ectofparasitismonhostsurvivalinameaningfulway. 4.3.4 InfectionDynamicsAllofthelongitudinalstudiesfoundthatpreva-lencevarieddynamicallyovertime,withcertain parasite speciesbeingseenonlyovershorttimein-tervals.Insomecases,thedynamicsappearcyclic,withseasonalreoccurrenceofparasites(mostlyinsummer),butforthemajorityofparasitespecies,itisunclearwhatdetermines abundance patterns.Extremecasesofparasitedynamicshavebeenob-servedinsomeofthelongerstudies,wherecer-tainparasitesdisappearedforextendedperiodsoftimeandthenreemergedwithoutanynoticeablereason( Green1974 ; Bittner2001 ).Itistotallyun-clearwhetherenvironmentalorevolutionaryfac-torsplayaroleintheseextremedynamics.Afewofthelongitudinalstudiesanalyzedthedynamicswithrespecttohostdensity.Thusfar,nostudyhasshownacleardensitye ect,al-thoughdensity-dependent transmission hasbeenshowninthelaboratory( Ebert1995 ; Bittneretal.2002 ).Somestudiesobservedthatparasitesrstappearedwhenhostdensitywashigh,butincontrasttowhatwouldbeexpectedifdynamicsweredrivenby densitydependence ,parasitesdidnotdeclinewhenhostdensitydeclined( Brambilla1983 ; YanandLarsson1988 ).Thistrendhasalsobeenobservedforparasitesofplanktonicrotifers( Miracle1977 ; Ruttner-Kolisko1977 ).Severalstud-iessuggestedthathostdensityandwatertemper-aturearetosomedegreeconfounded,becausethedensityofmostplanktonorganismsishighdur-ingthewarmerperiods.Therefore,itisnotcleartowhatdegreeelevatedtemperaturesplayaroleinsummer epidemics ( Green1974 ; Brambilla1983 ).Atleastforonemicrosporidium,ithasbeensug-gestedthatlowtemperaturecanhindertransmis-sion( Ebert1995 ).Thereare,however,severalre-portsofparasiteoccurrenceatlow(winter)watertemperatures,indicatingthattemperaturealonecannotexplaintheoccurrenceofepidemics( Stir-nadel1994 ; Bittner2001 ; Decaesteckeretal.2005 ).Apossibleexplanationcouldbethatparasitesdonotgrowatlowtemperaturesbutmaybeabletopersistforsometime.Therelationshipbetweenthespreadofparasitesinrelationtohostdensityandwatertemperaturecertainlyneedsfurtherinvesti-gation.Thecommunity-levelperspectiveof De-caesteckeretal.(2005) revealedremarkablepat-terns.Daphniadensitywasobservedtobeneg-ativelyrelatedwithoverall endoparasite preva-lence,whereas epibiont abundancecorrelatedpos-itivelywithDaphniadensity.Furthermore,parasitespeciesthatseverelyreducedhostfecundityper-sistedforshorteramountsoftimeinthepopula-tionandhad,onaverage,lower prevalences thanbenignspecies.Thedatadidnotallowaneres-olutionofthesepatterns,butthefollowinginter-pretationmayexplainthesendings.Higherhostdensityallowsparasitestospreadandthusin-creasesprevalence.Thus,harmlessparasites(suchasepibionts)aremoreabundantwhenhostden-sityishigh.Hereitisthehostthatgovernspara-sitedynamics.However,harmfulparasitesmayatthesametimereducethehostpopulationgrowthratesomuchthattheirnete ectonthehostpop-ulationisareductionindensity.Thisreductioninhostdensitydestabilizestheparasitepopulation,whichleadstoshortparasitepersistencetimes.Thus,forharmfulparasites,theepidemiologicalfeedbackbetweenhostandparasitegovernstheparasitedynamics.Thestrongdynamicsofmanyparasitespeciesalsoindicatethatstudiesthatuseonlyoneorfewsamplesperpopulationtoestimatethe richness of 38ParasitisminNaturalPopulations thelocalparasitecommunityarelikelytovastlyunderestimate parasiterichness . 4.3.5 AreThereFewerParasitesinLakeswithFish?Thereseemstobeadi erenceinthedegreeofpar-asitisminwaterbodieswithandwithoutplanktiv-oroussh.Thelower parasiterichness andpreva-lenceestimatesinlakeswithshpredationareun-derscoredbythefactthattherearefewerliteraturereportsofDaphnia parasites fromlakeswithsh.Severalfactorsmayworktogethertoexplainthisfact.First,thelikelihoodofinfectionincreaseswithbodysize( Vidtmann1993 ; StirnadelandEbert1997 ),whichisprobablyaresultofbothhigherltrationrates(andthushigheruptakeratesofpar-asitespores)andanaccumulatione ectwithage.Inpondswithhighadultmortality,asistypicalforpopulationswithplanktivoroussh,theaveragelifeexpectancyofaDaphniaislow,andthus,para-sitesmayhavealowerchanceofcompletingtheirdevelopment.Thisreducesnotonlyparasitesur-vivalbutalsoparasitetransmission,becauseolderinfectedhostsarethosethatreleasemost(orevenall)ofthetransmissionstages.Apredictionofthishypothesisisthatparasitesfoundinlakeswithhighpredationpressureshouldcompletetheirde-velopmentquickly(short prepatentphase )andthuskilltheirhostearly.ThemostvirulentDaphniaparasiteshavebeenindeeddescribedfrom habitats withplanktivoroussh( Bittner2001 ; Wolinskaetal.2004 ; Du yetal.2005 ).Anotherpredictionisthatparasitismratesinlakesshouldbehigherattimeswhenshpredationislow.Indeed,para-sitisminLakeConstanceismainlyfoundinfallandwinter( Bittner2001 )whenpredationisstronglyre-duced,whereasinshlesspondsandlakes,preva-lencepeaksinsummer( Brambilla1983 ; Vidtmann1993 ; Stirnadel1994 ). Du yetal.(2005) linkedtheseasonaloccurrenceofSpirobacillus epidemics inseveralNorthAmericanlakestoadropinpreda-tionratebybluegillsunsh.Second,somediseasesmaketheirhostsmoreconspicuousthroughareductionintransparency,thusincreasingthelikelihoodofpredationbyvisu-allyhunting predators ( Lee1994 ; YanandLarsson1988 )(P.T.J.Johnson,personalcommunication).Similarly,increasedsusceptibilitytopredationwasreportedforhostscarryinglargeloadsofepibionts( Willeyetal.1990 ; Allenetal.1993 ; Chiavellietal.1993 ; Threlkeldetal.1993 ).Consistentwiththis, WilleyandThrelkeld(1993) reportedareductionintheprevalenceofclearlyvisible epibionts afterstockingwithsh.Apredictionofthishypothesisisthatparasitesfoundinlakeswithvisuallyhunt-ingshshouldnotmaketheirhoststoovisibleor,ifso,onlyintheterminalphaseofinfection.Con-sistentwiththis,themainparasitesofD.galeataandD.hyalinainLakeConstancearehardlyvisiblewiththenakedeye( Bittneretal.1998 , 2002 ; Bittner2001 ).However,thishypothesisneedsfurthercare-fulexamination.Atwisttothishypothesisisthatinturbidwaterswithlowvisibility,infectedhostsmaynothaveareducedlifeexpectancyrelativetouninfectedhosts( Decaesteckeretal.2005 ).Third,sh predators aretypicallymorecommoninlargerpondsandlakes.Anumberoffactorsthatgohand-in-handwiththesizeoflakesmaylimitthespreadofparasites.Summertemperaturesinlargerwaterbodiesmaynotriseashighasinsmallerlakesinthesameregion,thusinuenc-ingparasitedevelopmentorshorteningtheseasonduringwhichparasitescanoccur( Ebert1995 ).Fur-thermore,thesedimentoflarger,andinparticulardeeper,lakesmaybeasinkforparasitetransmis-sionstages.Parasite spores areknowntorestinsediment,wheretheycanbepickedupbyDaphnia( Ebert1995 ; Decaesteckeretal.2002 ).Indeeplakes,Daphniaarelesslikelytocomeincontactwithlakesediment,thusreducingtransmissionrates.Apre-dictionofthishypothesisisthatparasitesthatrelyexclusivelyontransmissionfromdeadhostsarelesslikelytobefoundindeeplakes(see Chapter8 , Epidemiology ,sectiononTransmission),asforex-ampleP.ramosa.Indeeplakes,transmissionfromlivinghosts(e.g.,gutparasites)maybemuchmoreimportantforthepersistenceofparasites.Fourth,becauseDaphniapopulationsinlakesmaynotreachthedensitylevelsofpondpopula-tions,parasitetransmissionmaybereduced.Twofactorsmayaccountforthissituation:a)lakesareoftenlessnutrientrich(eutrophic)thanponds,sothatlowerratesofprimaryproductionmaylimitthemaximumdensityof zooplankton populations;andb)predationbyplanktivorousshmayinu-enceDaphniadensity,andthusparasitetransmis-sion,negatively. 5.2E ectsonHostFecundityandSurvival43 Figure5.1Thee ectoffourparasitespeciesonrelativefecundityandsurvivalofDaphniamagna.Relativefecundityiscalculatedasthetotalnumberofo springofaninfectedfemale(untilherdeath)relativetothetotalnumberofo springofanuninfectedfemale,assumingthatthehealthyfemalewouldhavediedthesamedayastheinfectedfemale.Thus,theserelativefecunditymeasuresarenotconfoundedwithdi erentlifeexpectanciesofinfectedanduninfectedfemales.WFCD,WhiteFatCellDisease;P.ram.,P.ramosa;M.bic.,Metschnikowiabicuspidata;G.int.,Glugoidesintestinalis.Redrawnandadaptedfrom Ebertetal.(2000a) . galeataproducedmoreeggsunderlowfoodcondi-tionsthanunderhighfoodconditions.IncontrasttothefoodstudyinD.galeata,astudyonD.magnainfectedwithP.ramosafoundthatwell-fedinfectedhostsproducedmoreeggsthanpoorlyfedinfectedhosts( Ebertetal.2004 ).Interestingly,thewell-fedinfectedhostsalsoproducedmoreP.ramosa trans-mission stages,indicatingthatgoodfeedingcon-ditionsbenetboththehostandthe parasite .Bothantagonistsarepossiblyresourcelimited.TemperatureE ectsHealthyDaphniamatureearlierandatasmallersizeandhaveashorterlifespanwhengrowingun-derconditionsofhighertemperature.SurprisinglylittleisknownabouttheinuenceoftemperaturefortheexpressionofdiseaseinDaphnia. Du yetal.(2005) reportedanecdotallythatD.dentiferain-fectedwithSpirobacilluscienkowskiisurvivelongeratlowertemperatures.Becauseusuallyeverythingwithinvertebratestakeslongeratlowertempera-ture,thisobservationmaysimplybetheresultofthehosts'and parasites 'lowermetabolicrates.Amorecomplexrelationshipbetweentemperatureanddiseaseexpressionwasreportedby Mitchelletal.(2005) .Theyfoundthatthenegativee ectofP.ramosaonD.magnafecunditywasmorebe-nignwhenthetemperaturewaslower.Atalowertemperature,theparasitegainedlatercontroloverhostfecundity.Theauthorsemphasizethatthisef-fectweakensparasite-mediated selection duringpartoftheseason.Furthermore,thisparasitee ectinteractedbothwithhost genotype andtempera-turesuchthatclonalranksinhosttnessdi eredunderdi erenttemperatureconditions.Thise ectcannotbeexplainedbythetemperaturedepen-denceofmetabolicrates.Alteredrankordersof 44TheE ectsofDaphniaParasitesonHostFitness hostgenotypesmayhaveprofoundconsequencesforthe evolution ofhost resistance .However,itisnecessarytoseetheseinteractionsinrelationtothemaine ectsandtheseasonaldynamicsofthediseasetojudgehowevolutionwillbeinuenced.ChemicalCuesfromPredatorsDaphniahavebeenaworkhorseforthestudyof phenotypicplasticity .Inparticular,theirreac-tiontochemicalcuesreleasedby predators (i.e., kairomones )hasreceivedalotofattention. LassandBittner(2002) testedforinteractionsbetweenthee ectsoftwoantagonistsonD.galeata,thepro-tozoangut parasite C.mesniliandkairomonesfromplanktivoroussh.Theyfoundnoevidenceforin-teractionsbetweenshandparasitewithregardtohostfecundityandsurvival.DoseE ectsAnotherenvironmentale ectthatinuencestheharmcausedby parasites isthedoseoftransmis-sionstagestowhichahostisexposed.Typically,higherdosesgohand-in-handwithahigherlike-lihoodofinfectionandwithmoreseveredamagetothehost( Ebert1995 ; Ebertetal.2000b ; Regoesetal.2003 ; Ebertetal.2004 ).Veryhighdosesmayevenharmthehostsomuchthattheparasiteisnotabletocompleteitsdevelopmentbeforethehostdies( Ebertetal.2000b ). 5.2.2 GeneticE ectsGeneticVariationamongHostsandParasites Parasitevirulence variesacrossparasiteisolates(strains,genotypes)andhostclones.Tomyknowl-edge,everyattempttotestfor geneticvariation withinparasite-inducedhostdamageintheDaph-niasystemhasshownsignicante ects.Hostclonesoriginatingfromwithinorbetween pop-ulations di erinthedegreewithwhichtheyex-pressdiseasesymptoms,andparasiteisolatesvarygreatlyintheextenttowhichtheycausedamagetothesamehostclones( Ebert1994a ; Ebert1998a ; LittleandEbert2000 ; Bittner2001 ; Decaesteckeretal.2003 ).Furthermore,therearestronghostclonexparasiteisolateinteractions:Withinpopulations,theinfectivityofP.ramosadependsstronglyontheinteractionbetweenthePasteuriaandtheD.magnagenotypes( Cariusetal.2001 )( Figure5.2 ).Thesameistrueiffecundityreductionisconsid-eredamonginfectedfemalesonly( Cariusetal.2001 ).Whatmaintainsthesehighratesofwithin-populationvariationisnotfullyunderstood,butithasbeensuggestedthatantagonistic armsraces playakeyroleinmaintaining geneticvariation forvirulenceand resistance ( Hamilton1980 ; EbertandHamilton1996 ; Cariusetal.2001 ).GeneticVariationacrossPopulationsandLocalAdaptation Geneticvariation for parasite virulenceismostpro-nouncedacrosspopulations.Thisvariationoftenfollowsacertainpattern,whichisfrequentlydis-cussedinthecontextof localadaptation ( KaweckiandEbert2004 ).ForfourD.magnaparasites,ithasbeenshownthatlocalparasiteisolatescausemoreharmtotheirhoststhanparasiteisolatesfromotherpopulations( Ebert1994b ; Ebert1998a )(D.RefardtandD.Ebert,manuscriptinpreparation).Thesendingsareconsistentwiththeideathatpara-sitesevolvelocaladaptationtothehoststheyhaveencounteredrecently( Figures5.3 and 5.4 ).Often(butnotalways)parasitesthatperformbetterintheirlocalhostthanotherforeign(ornovel)para-sitesalsoperformbetterintheirlocalhoststhaninotherhosts( Figures5.3 and 5.5 ).Locallyadaptedparasitesshownotonlyhigherlevelsofdamagetotheirlocalhostsbutalsohavehigherlevelsoftransmission-stageproduction( Ebert1994b ).Thendingofparasite localadaptation seemsrathergeneralinDaphniasystemsbutisnotal-waysfoundinotherhost–parasitesystems.Someauthorsreportedthathosts,ratherthanparasites,canbelocallyadapted( Morandetal.1996 ; KaltzandShyko 1998 ; Kaltzetal.1999 ).Ithasbeensuggestedthatthekeyvariablefortheevolutionofhostorparasitelocaladaptationistherelativespeedofevolutionofthetwoantagonists( Gandonetal.1996 , 1997 ; Gandon2002 ).Higherratesofmu-tation,recombination,anddispersalmayfacilitatelocaladaptation.Giventhesetheoreticalconsider-ationsandthendingthatDaphniaparasitesseemtobelocallyadapted,onemayspeculatethatpara-sitesofDaphniausuallyhaveahigherevolutionarypotentialthantheirhosts.Adi erentapproachtohost–parasiteinterac-tionsacrosspopulationsisthequestionofhow 46TheE ectsofDaphniaParasitesonHostFitness Figure5.3LocaladaptationofG.intestinalisinD.magna.StrainsofthemicrosporidiumG.intestinalisfromthreedi erentD.magnapopulationsshowthehighestratesofsporeproductionwheninfectinghostsfromthetheirownnativepopulation(bluecolumns).Thesamestrainsincombinationwithhostsfromfourotherpopu-lations(graycolumns)producemuchfewertransmissionstages.Notethelog10scaleforsporecounts.PopulationsHost1,Host2,andHost3arefromsouthernEngland,populationHost4fromsouthernGermany.Formorein-formation,see Ebert(1994b) . muchadispersinghostsu erswhenitencountersalocallyadaptedparasiteinanovelpopulation.Notethatthisquestionisdi erentfromtheques-tionaboutparasite localadaptation . KaweckiandEbert(2004) explainthesedi erencesinfulldetail.Ifparasitesarelocallyadaptedandthuscausemoreharmtotheirlocalhosts,ahostthatmigratesintosuchapopulationshould,oneexpects,su erlessonaveragefromthelocalparasitesthanthelocalhosts.Thisobservationhasbeenreportedinsev-eralexperiments( Ebert1994b ; Ebertetal.1998 ; Al-termatt2004 ).Itisimportanttonotethatalthoughthispatternisfoundwhenaveragingacrossseveralhost–parasitecombinations,occasionallyahostinanovelcombinationismuchmorea ectedbythe Figure5.4LocaladaptationofP.ramosainD.magna.Threedi erentstrainsofthebacteriumshowthehighestwithin-hostgrowthrateswheninfectinghostsfromtheirownnativepopulation(bluecolumn)(meanandstandarderror).OtherPasteuriaisolates(Novel)testedinthesamehostclones(graycolumn)havelowergrowthrates.Formoreinformation,see Ebert(1998a) . newparasitesthanexpected( Ebert1994b ).Theseinstancesarelikelytobeexceptions,buttheymayhaveprofoundconsequences,becausetheymaybethebeginningofadevastating epidemic .Furtherinformationaboutthe evolution ofvirulencecanbefoundinanumberofreviews( Bull1994 ; Ebert1998a , 1999 ; EbertandBull2003 ). 5.3 ParasiteE ectsonOtherHostTraitsBesidesfecundityandsurvival, parasites mayinuenceotheraspectsofhost tness ,fewofwhichhavebeenstudied.G.intestinalis(formerlyPleistophoraintestinalis)reducesadultgrowthinitshostD.magna( Ebert1994b ).Thestrengthofthisef-fectwasshowntodependbothonhostcloneandparasiteisolate,withlocalparasiteisolateshaving 5.3ParasiteE ectsonOtherHostTraits47 Figure5.5O.bayerisporeproductioninclonesofitsnativeD.magnapopulationandinclonesfromthreeotherD.magnapopulations.TwostrainsofO.bayerioriginatingfromtwoislandsofarockpoolmetapopulationofD.magnainsouthernFinlandweretestedincombinationwiththeirownandthreecentralEuropeanpopulationsofD.magna.Means(acrossclones)andstandarderrorsaregiven(between4and11cloneswereusedperhostpopulation).Formoreinformationon“MaterialandMethods”,see Mucklowetal.(2004) . 48TheE ectsofDaphniaParasitesonHostFitness thestrongeste ect. LassandBittner(2002) showedthatC.mesnilireducedtheadultgrowthofitshostD.galeata.Incontrast,P.ramosacausesitshostD.magnatogrowtoanunusuallylargesize( Ebertetal.1996 , 2004 ).Thisformofparasite-inducedhost gigantism maybeadaptivefortheparasite,aslargerhostsresultinmoreparasite spores beingproduced( Ebertetal.2004 ).Parasitesmayalsoinuenceaspectsoftheirhosts'sexuallifecycle.Forexample,theymayre-ducethehosts'likelihoodofndingmatesormayincreaseordecreasethefrequencywithwhichafemaleproducesephippiaandmaleo spring.Fur-thermore,verticallytransmittedparasitesmayin-uencethesurvivaloftheirhostduringresting( LassandEbert2005 ). 5.4 ParasitesMayInuencePredationonTheirHostsThepotentiale ectthat parasites haveonhost–predatorinteractionsisalsoimportant.Para-sitesmaylowertheabilityoftheirhoststoescape predators ;infectedhostsmayswimandreactmoreslowlythanhealthyhosts,forexample.Thesome-timesdramaticvisuale ectthatparasiteshaveonDaphniamayevendirectlyincreasethehosts'at-tractivenesstovisuallyhuntingpredators( YanandLarsson1988 ; Lee1994 ; Du yetal.2005 ). LassandBittner(2002) testedformoreindirecte ectsofparasitesonhost–predatorinteractions.TheytestedwhetherhostsarelessabletoshowadaptivephenotypicchangesagainstpredatorswhenexposedtoC.mesnili.Theirexperimentsre-vealednosignicantinteractionsbetweenparasiteandkairomon-inducedlifehistorychanges.Theyconcludedthatthisisbecausethehost'sadaptiveresponseagainstshpredatorschangeslifehis-torytraitsexpressedearlyduringthehost'slife,whereastheparasitea ectsitshostduringlaterstages.Ontheotherhand,onecanimaginethatpara-sitesaltertheirhost'sbehaviorsothathostsmoree ectivelyprotectthemselvesfrompredators,e.g.,byaltering verticalmigration .Thismaystillbedisadvantageousforthehostbecausethepara-site'sinterestisinhostsurvival,whilethehosthasto trade-o protectionfrompredatorsagainstother tness components,suchasreproduction. Lee(1994) and Felsetal.(2004) showedthatvar-iousparasitespeciesinuencethe depthselectionbehavior ofD.magna.Infectedhostsstaydeeperinthewaterthanuninfectedcontrols.Itisnotclear,however,whetherthisisadaptiveforthehost,theparasite,both,ornone.Anextremeexampleofalteredpredatorexpo-surewouldbeacaseinwhichtheparasitema-nipulatesitshost'sbehaviortofacilitateitown transmission tothenexthost.Tomyknowledge,noneofthedescribedunicellularparasitesofDaph-niahasaknownsecondhost,althoughthisoptionhasbeenspeculated( Manginetal.1995 ).However,the macroparasites ( helminth )parasitesofDaphnia,whichhavenotyetbeenextensivelystudied,havesecondhostsandmaywellmanipulatetheirhoststotheirownadvantage( Stammer1934 ; Green1974 ; SchwartzandCameron1993 ). 5.5 ConclusionsandOpenQuestionsThereislittledoubtthat parasites ofDaphniaandother Cladocerans aregenerallyharmful.Occa-sionalreportsof"nonsignicant"e ectsofpara-siteshavetobeconsideredinthelightoflowsta-tisticalpowerorlargeenvironmentalnoise.Thusfar,everyspeciestestedundercontrolledcondi-tionsprovedharmful.WhatIndmoreinterest-ingthanthefactthattheparasiteharmsitshostarequestionsregardingthecovariablesofthede-greeofharm.Thereareanumberofinterestingquestionsaboutthis: 1. Whyaresomeparasitesmoreharmfulthanothers?Whatroledoestheparasite'staxo-nomicpositionplayforits virulence ?Whatroledoesthemodeof transmission play?Whatroledoesthespecictissueinfectedplay? 2. AretherefurtherhiddencostsofparasitisminDaphnia?Forexample,doparasitesinu-encematechoiceduringsexualreproduction?Doparasitesinuencethesurvivalof restingeggs ? 3. Doesinter-andintra-speciccompetitionofparasitesinuencevirulence? Chapter6HostAdaptationsagainsttheCostsofParasitism Asparasitesharmtheirhosts,thehostmaycounteradapt,reducingthetnesscostsofpara-sitism.HereIsummarizethelittleweknowaboutthewaysDaphniaadaptstolowerthecostsofparasitism.OneknownexampleisthatD.magnamaturesearlierinthepresenceofinfec-tions.IfurtherdiscusswhatisknownaboutinduceddefenseandtheevolutionofresistanceinDaphnia.Thechaptercloseswithadiscussionofthelimitsofhostresistance.Thusfar,noevidenceforacostofdefensehasbeenfoundinDaphnia. 6.1 Introduction Parasites harmtheirhoststofostertheirownneeds.Asstudiesthusfarhaveshown,thisdamagevariesacrosshostclones,suggestingthepresenceof geneticvariation amonghostsfor resistance ortheexpressionofdisease.Thisgeneticvariationfortness-relatedtraitsmaybringaboutdi erentreproductionandsurvivalratesamonghost geno-types ,sothathostclonesthatsu erlessfrompar-asitismincreasetheirnumericalrepresentationinthehost population .Ifatleastpartofthegeneticvariancefortnessisbasedon additivegeneticvariance ,thehostpopulationmayadapttocoun-teractparasitesevenacrossthesexuallifecycle,i.e.,evenafterthegenecombinationsintheclonesarerecombinedintonewgenotypes.Thusfar,wehaveonlyafewclearexamplesofDaphniahostsadaptingtoparasitism.Therearetwomainproblemswithdetectinghostadapta-tions.First,ifhost adaptations lowerparasite t-ness (whichisoftenbutnotnecessarilyalwaysthecase),parasitesmayrapidlyevolvecounteradapta-tionsthatreducethee ectivenessofthehostadap-tationsandmaymaketheminvisible.Apredictionofthistheoryisthathostadaptationsaremorelikelytobefoundinthepresenceofcoevolvingparasitesiftheadaptationbenetsthehostgreatlybutposeslittleornodisadvantagetotheparasite.Forexample,thereductionof"unnecessary viru-lence ",i.e.,parasite-induceddamagetothehostthathasnobenetfortheparasite,couldbeaneasilydetectedhostadaptation(innovel,notyetcoevolved,host–parasiteassociations,suchunnec-essaryvirulenceissometimesobserved).Second,theadaptivevalueofhosttraitsexpressedinthepresenceofparasitesmaybediculttojudgebe-causetheystemfromtheinteractionbetweentwoorganismsandmayormaynotbebenecialtoboth( Moore2002 ).Forexample,istheDaphnia'sparasite-inducedchangein dielverticalmigration ( Felsetal.2004 )benecialforthehost,theparasite,both,ornone?Hostadaptationstoparasitesmaybeobservedatseverallevels.Themostimpressiveexamplesarethosewhereatraitisexpressedonlyinex-posedorinfectedindividualsandconfersabene-tcomparedwithindividualsthatdonotexpress 66Epidemiology Figure8.4ProportionofinfectedD.magnarelativetothenumberofP.ramosasporesinthemedium.Thesig-moidalincreaseinproportionofinfectedhostsfollowstheexpectationofthemassactionmodelclosely.Eachsporedosewasreplicatedabout100times.Redrawnaf-ter Regoesetal.(2003) . tosusceptibility( LittleandEbert2000 ; Cariusetal.2001 ).ParasiteTransmissionCanBeLimitedbyLowTemperaturesPlanktonepidemicsarepredominantlyfounddur-ingthewarmsummermonths( Green1974 ; Brambilla1983 ; YanandLarsson1988 ; Vidtmann1993 ). Ruttner-Kolisko(1977) ,workingwithami-crosporidian parasite inarotifer population ,pro-posedthat transmission isimpairedatlowtem-peratures.ItestedthishypothesiswithG.intesti-nalisinD.magnaandfoundthattransmissionwasindeedimpairedbelow12C( Ebert1995 ).ThisisconsistentwiththeobservationthatG.intestinalisdecreasedinlateautumninD.magnapopulationsinsouthernEngland( Stirnadel1994 ).Poortrans-missabilityattemperaturesbelow25Cwasre-portedforP.ramosa,whichparasitizestheClado-ceranMoinarectirostris( Sayreetal.1979 ).(Note:ItisquestionablewhetherthisMoinaparasitewasindeedP.ramosa.)Incontrast,P.ramosainD.magnacanbetransmittedbetween10and25Cinthelaboratory( Ebertetal.1996 ; Mitchelletal.2005 ).Thus,temperaturecriterionappearstobespeciesandstraindependent.ReportsofnaturalDaphniapopulationsfurtherindicatethatcertainparasitescanbefoundunderwinterconditions( Stirnadel1994 ; Bittner2001 ).InLakeConstance,Daphniaparasitesoftenoccurpre-dominatelyinfallandwinterconditions( Bittner2001 ),suggestingthattemperatureiscertainlynotuniversalinlimitingparasitespread.Theabsenceofparasitesduringsummerinlargelakeshasbeensuggestedtoberelatedtointensepredationduringsummermonths( Du yetal.2005 )andisunlikelytobeaconsequenceoftemperaturee ectsontrans-mission.HostStressMightFacilitateParasiteSpreadIthasbeenclaimedthatstressedhost populations aremore susceptible to parasites andthusfacilitateepidemics.ThistheoryhasbeenusedtoexplaindiseaseoutbreaksinCladoceranskeptunderpoorlaboratoryconditions( Seymouretal.1984 ; Stazietal.1994 ).Likewise, FranceandGraham(1985) observedhigherratesofmicrosporidiosisamongstressedcrayshinacidiedlakes.ForDaphnia,thereisnosupportforthestresshypothesisbutrathertheopposite.Experimental transmission ofG.intestinalistoindividualD.magnaappearedtobelargelyindependentofthehost'sfeedingcon-ditions(anddidnotdi eramongagegroupsorsex)( Ebert1995 ).SimilarresultswereobtainedforC.mesniliinD.galeata( Bittneretal.2002 ).Adirecttestofthestresshypothesiswascarriedoutinex-perimentalpopulationsofD.magnainfectedwithG.intestinalis.Whenhalfoftheexperimentalpopu-lationswerestressed(reducedfoodlevel),parasitepopulationssu eredmorethanthehostpopula-tions( PulkkinenandEbert2004 )becausemortal-itywasdisproportionatelyhigheramongthemostheavilyinfectedhosts(thosethatcarriedthemostparasites).Thisresultcountersconventionalwis-domaboutvertebratepopulations,inwhichstressisthoughttogohand-in-handwithdiseaseout-break.Experimentsthattestedtherelationshipbe-tweentransmissionstageproductionandhostnu-tritionalstatusfurthersupporttheobservationthatDaphniaparasitesdonotfarewellwhentheirhostsarestressed.Asinotherinvertebratesystems,par-asitesinpoorlyfedhostsproducefewertransmis-sionstagesthanparasitesinwell-fedhosts( Ebertetal.1998 ).Thus,althoughsomeobservationshavebeeninterpretedtosuggestthatstressmayleadtodiseaseoutbreaks,experimentalresultsshow 68Epidemiology Figure8.5Variationinresistanceamong19D.magnaclonesinresponsetoveparasitespecies.Micro1and2aretwoundescribedmicrosporidianparasitesofD.magna.Allhostclonesandparasiteisolatesoriginatedfromthesamepopulation.Redrawnandmodiedafter Decaesteckeretal.(2003) . diapause,Daphniahatchfromtheir ephippia andrecolonizeapond.Undergoodfeedingconditions,thepopulationincreasesrapidlyduringspringun-tilfoodshortagesleadtoaswitchfromlterfeed-inginthefreewatertobrowsingonthebottomsed-iments.Browsingsupplementsthefoodbecauseitstirsupfoodparticles( Hortonetal.1979 ; Freyer1991 ),whicharetheningestedbylterfeeding.However,browsingalsostirsupparasite transmis-sion stages,whichmayinfectthedaphniid.Oncethersthostsareinfected,thediseasemayspreadfurther.Theepidemicendseitherwhenenviron-mentalconditionsdeteriorate(e.g.,lowtempera-ture)orwhenthehostpopulationbecomessparseordisappearsaltogether.Akeyfeatureofthismodelistheuptakeof spores fromthepondsediments,whichhasveryimportantconsequencesforthe epidemiology ofthesystem,aswasshowninamathematicalver-sionofthismodel( Ebertetal.1997 ).First,uptakeofsporesfromthesedimentsisindependentfromhostdensity.ThebasicreproductiverateR0be-comesredundantasameansofpredictingpara-sitepersistencewhenthereisalarge,nondeplet-ingsporebankinthesediment.Instead,thefeed-ingbehaviorofDaphniaandthepropertiesoftheresourcedetermineparasiteinvasions.ThismayexplainwhylongitudinalstudiesofDaphniapond populations havefailedtondarelationshipbe-tweenparasitismandhostdensity.Second,the sporebanks allowtheparasitestosurvivelongperiodsoflowhostdensity.Althoughthisepidemiologicalmodelwasdevel-opedforponddwelling zooplankton ,itsndingsaboutdensity-independentinfectioncouldalsoberelevanttoanumberofsoil-bornediseases. Flem-ingandcolleagues(1986) investigatedthedensity-dependenttransmissionofavirusindi erentpopulationsofthesoil-dwellingpasturepestWis-canasp.(Lepidoptera:Hepialidae).Evidencefordensity-dependenttransmissionwasfoundonlyinyoungpasturesbutnotinoldpastures,per-hapsbecauseinolderpasturestransmissionoc-curredmainlyfromasporepoolthathadaccumu-latedoverseveralgenerations.Inlaboratorypopu-lationsofavirus–insectsystem,Saitandcolleagues( Saitetal.1994 )failedtodetect densitydepen-dence andattributedthisresulttotherapidaccu-mulationandlongpersistenceofvirustransmis-sionstageswithinthecages.Contaminationofthesoilhasbeenrepeatedlycitedasthesourceofvar-iousinfections( KellenandHo mann1987 ; Young1990 ; Woodsetal.1991 ; Daietal.1996 ).Thus,itappearsthatdurabletransmissionstagesandtheiraccumulationinpondsedimentsorsoilmightbeawidespreadphenomenoninnaturalhost–parasitesystemsandmayobscureanypatternofdensity-dependenthost-to-hosttransmission.TheDaphnia–parasitemodelforshlesspondso ersonlythemostbasicpatternofparasitedy- 8.2EpidemiologyofDaphniaMicroparasites69 Figure8.6Di erenceinsusceptibilityofeitherinfectedorhealthyD.magnacollectedfromanaturalpopulation.Allfemaleswerecuredandreinfectedunderstandardizedconditionswithdi erentdoses(sporesofP.ramosaperhost).Inthreeoffourpopulations,thedescendantsofpreviouslyinfectedfemalesweremoresusceptibletoinfectionunderstandardizedlaboratoryconditions.Modiedafter Little&Ebert(2000) . 70Epidemiology namics,leavingmanydetailsunexplained.Itcan-not,forexample,explainthedynamicsofpreva-lenceinlakeswheretherearelikelytobenosporebanksandmayalsofailtopredictepidemicsinpondswithpermanent(withoutdiapause)Daphniapopulations.Itisfurtherunabletoexplainwhycer-tainparasitespeciesshowshort-lastingepidemicsofafewweeks.Clearly,ourunderstandingofpar-asitedynamicsinnaturalDaphniapopulationsisstillverylimited. 8.2.2 SuggestionforaLakeModelAsdiscussedabove,lakeswithshpredationseemtohavelowerratesofparasitismthanshlessponds(see Chapter4 onDaphnia Microparasites inNatural Populations ).Thefollowingmodelmaybeastartingpointforunderstanding zooplankton epidemicsinlakeswithsh.MyideasarepartiallybasedontheworkofKerstinBittneratLakeCon-stance( Bittneretal.1998 , 2002 ; Bittner2001 ).FishpredationcanbeaseveremortalityfactorforDaphniaandwillcertainlyinuencethe abun-dance ofparasites.Ifshpredationishigh,para-sitesmaynotbeabletospreadinDaphniapop-ulations,becausetheaveragelifeexpectancyofaDaphnia(andthusofaninfection)istooshort(see Chapter4 ,AreThereFewerParasitesinLakeswithFish?).K.PulkkinenandD.Ebert(manuscriptinpreparation)haveshownhighparasiteextinc-tionratesinarticiallypredated,experimentalD.galeatapopulations.Thus,duringperiodsofhighpredation,parasitesareexpectedtobeabsentorfoundinlowprevalence.Becausepredationpres-sureoftenvariesovertime,parasitesmayspreadduringperiodswhenadulthostmortalityisrela-tivelylow.ThistheorycoincideswithndingsthattheprevalenceofDaphniaparasitesinlakepopu-lationsishighinfallwhenshpredationislow,whereasparasitesareabsentoronlyfoundinlowprevalenceduringsummertime,whenpredationishigh( Bittneretal.2002 ; Du yetal.2005 ).Inshlessponds,parasitessurvivetheabsenceoftheirhostsinthesediments.Becauselakeswithsharelesslikelytohaveecologicallyimportant sporebanks inthesediments(Daphniaaremuchlesslikelytocomeintocontactwiththesedimentinlakes),adi erenthypothesisisneededtoexplainhowtheseparasitescansurviveunfavorablecon-ditions.Apossibleexplanationmightbethelargesizeofplanktonpopulations,whichmayenableparasitestosurvivelongperiodsofnegativepopu-lationgrowth(R01).Withahugehostpopulationsize,forexample,aparasitepopulationmightde-clineconsiderablyforseveralgenerations,reach-ingverylowprevalence.Butlowprevalenceinlargelakesishardlyanindicationofextinction.Forexample,inalakethesizeofLakeConstance(volume,50x109m3),ifthehostdensityfallsto0.1Daphniaperm3and1in100,000hostsisin-fected,therewouldbestillabout50,000infectedhosts,certainlyenoughtomaintaintheparasitepopulation,althoughatlevelsfartoolowtobede-tectedwithconventionalsamplingmethods.Thisargumentneedscarefulevaluation,takingabso-lutehostandparasitepopulationsizesintoaccountaswellasyear-roundgrowthconditions.Analternativehypothesisisthatparasitesgoex-tinctlocallybutoccasionallyrecolonizethelake.However,ifonlyoneorafewimmigrantparasitesareintroducedintoalargehostpopulation,theirspreadtodetectablelevelstakesconsiderabletimeunlessR0ishigh(»1).Nevertheless,thismecha-nismmaystillexplainsomeoftheobservedcasesofparasitedisappearanceandreappearance.Asmentionedabove,parasitesinlargelakeswithshpredationmayevolvecertainstrategiestoreducetheirmortality.Themostobviousofthesearefastdevelopment(evenifithascostsintermsofhigh virulence )andlowvisibilitytovisuallyhunt-ingsh.Acomparativestudybetweenlakeswithandwithoutshpredationwouldallowthesetwopredictionstobetested.Insummary,parasitesmaybeabletosurviveinlargelakeswithshpredationbyexploitinghostsattimesoflowpredationpressureandoutlastingunfavorabletimesinastateofextendednegativepopulationgrowth. 8.3 ConclusionsandOpenQuestionsAtpresent,wehavenosatisfactorymodelforthe epidemiology ofDaphnia parasites ,norofanyother zooplankton parasite.Thetwomodelspre-sentedabovearegeneralframeworksthattreatallparasitespeciesofacommunityalikeandthuslackmanyimportantfeatures.Amoreprotableap-proachmaybetofocusoncertainparasitespecies 74PopulationDynamicsandCommunityEcology Mathematicalmodelspredictdi erentpopula-tiondynamicsforhostsinfectedwithmicropar-asitesthatreducehostfecundityversusthosein-fectedwithparasitesthatreducehostsurvival( An-derson1979 , 1982 ).Hostdensityispredictedtodecreasemonotonically,withthenegativee ectthataparasitehasonhostfecundity(allotherthingsbeingequal).Incontrast,meanhostpopula-tiondensityispredictedtorstdecreaseandthenincreaseasparasite-inducedhostmortalityrises.Thisisbecause(foragiven transmission ratepa-rameter)parasitesthatkilltheirhostsveryrapidlyarelesslikelytobetransmittedtootherhostsandwill,therefore,remainatlowprevalence,whereasparasiteswithlittlee ectonhostmortalitywillhavelittlee ectonhostdemographics.Theseepi-demiologicalmodelsalsopredictpopulationuc-tuations,positingthathostdensityuctuationsin-creaseasamicroparasiteshowsanincreasinglynegativee ectonhostsurvivalandfecundity.Ac-cordingtothesemodels,densityuctuationsin-creasethechanceofextinctionofsmallhostpop-ulationsbecausehostdensityismorelikelytodroptozeroduringpopulationbottlenecks( May1974 ; McCallumandDobson1995 ).Epidemiolog-icalmodels,suchasthosecitedabove,haveoftenbeenusedtoexplainempiricalresultsinsituationswhereparasitesreducedthedensityoftheirhostsorcontributedtotheextinctionofthehostpopu-lation.Thesamemodelspredictthatbenignpara-siteshavelittlee ectonhostpopulationdensitiesandthereforecanbeappliedequallywelltocaseswhereparasiteshavelittleornoapparente ectonhostpopulationdynamics.Therefore,alongwithcontrastingparasitizedwithnonparasitizedpopu-lations,itisimportanttocomparehostpopulationsinfectedbyparasiteswithdi erente ectsonhostfecundityandsurvival. 9.2 DoParasitesRegulateHostPopulations?AreviewofeldstudiesonparasitisminDaph-nia populations (see Chapter4 ,GeneralizationsaboutParasitisminNaturalPopulations)revealsverylittleaboutthepopulation-levele ectsof par-asites ontheirhosts.Becausetherearenoreplicatesorcontrolpopulationswithoutparasitesineldstudies,itisdiculttodrawconclusionsaboutpopulation-levele ects.Tomyknowledge,only Brambilla(1983) hasattemptedtoanalyzehisdataforpossiblepopulation-levele ectsofparasitism.Hetestedforthee ectofthemicrosporidiumThe-lohaniaontheinstantaneousbirthanddeathratesinalongitudinalstudyofaD.pulexpopulationandcomparedtheserateswithratescalculatedundertheassumptionthattheparasitewasabsentfromthepopulation.Theimpactoftheparasiteonbirthratevariedwidelyoverthesummerandacrosstheyearbutwasgenerallystrongerthanitwasforthedeathrate.Fornearlyallsamplingdates,hecalcu-latedthattheparasitesdecreasedthe populationgrowthrate ,r,byabout20%onaverage.Hestates,however,thattheparasitealoneprobablydoesnotregulatethepopulationgrowthofitshost,becauservariedsubstantially,independentofparasitism( Brambilla1983 ).Hewasnotabletocarryoutlab-oratoryexperiments.Population-levelexperimentswithDaphniapar-asiteswererstproposedby EbertandMangin(1995) ,whoshowedthatD.magnapopulationsin-fectedwiththemicrosporidiumFlabelliformamag-nivora(intheirpapercalledTuzetiasp.)hadalowerdensitythanuninfectedcontrolpopulations.Thisparasiteisexclusivelyverticallytransmittedunderlaboratoryconditions( horizontaltransmission hasnotbeenfoundforthisparasite)andwaspresentataprevalenceof100%.Therefore,onecanexcludedensity-dependenttransmissionastheregulatoryfactor.Becauseexclusivelyverticallytransmittedparasitesinasexualpopulationsbehavelikeadele-teriousgene( Manginetal.1995 ),thereducedden-sityisadirectconsequenceofthereducedfecun-dityandsurvivalofthehosts. Ebertetal.(2000a) comparedthee ectsofsixparasitesonthefecundityandsurvivalofindi-vidualhoststotheire ectsonhostpopulationdensityandthehost'sriskofextinction.Fivehori-zontallytransmitted microparasites (twobacteria:WhiteFatCellbacterium,Pasteuriaramosa;twomi-crosporidia:Glugoidesintestinalis,Ordosporacolli-gata;onefungus:Metschnikowiabicuspidata)andsixstrainsofaverticallytransmittedmicrosporidium(F.magnivora)ofD.magnawereused.Lifetableexperimentsquantiedfecundityandsurvivalinindividualparasitizedandhealthyhostsandcom-paredthesewiththee ectoftheparasitesonhostpopulationdensityandonthelikelihoodofhostpopulationextinctioninmicrocosmpopulations. 78PopulationDynamicsandCommunityEcology Figure9.2RelationbetweenthedensitiesofColaciumvesiculosumandperitrichsonD.magna.Thesedataarecollectedfromanaturalpopulation.InexperimentsitwasshownthatlightfavorsC.vesiculosumoverper-itrichs,whereasdarknessfavorsperitrichsoverC.vesicu-losum.Thisindicatesthatthenegativecorrelationintheabundanceofthesetwoepibiontsisdrivenbyinterspe-ciccompetition.Redrawnfrom Green(1955) . peritrichciliates(favoredunderpoorlightcondi-tions).Acrossseveralindividualswithinapopu-lation,thiscompetitionleadstoanegativecorre-lationbetweenthenumberofperitrichsandthenumberofC.vesiculosum( Figure9.2 ).Thestrongvariationinepibiontcompositionacrossindivid-ualsmayreectindividualdi erencesinbehav-ior.Forexample,cloneswithaphototactic-positivebehaviormayhavemorealgaethanphototactic-negativeclones.Thesendingsclearlydemonstratethestrengthofwithin-hostcompetitionforshapingentire metapopulation communities.Theclearnessofthepatternsissurprising,however,giventhatsimi-larstrongpatternsarerarelyseenfromotherpar-asites.Ispeculatethatacombinationofspecichost–epibiontinteractionfactorsplayarolehere.First,Daphniamolteveryfewdays(1-2daysasjuvenilesand3-4daysasadultsat20C).Aftermolting,the carapace isclean,andepibiontsstrug-gletorecolonizeit( Threlkeldetal.1993 ).Thus,competitionforspaceisresetaftereverymolt,stronglydiminishingtheroleofhistory(whocolo-nizesrst)andleadingtostrongerhomogenizationamonghostsintheentirepopulation.Second,thelow virulence (harmdonetothehost)causedbyepibiontsdecoupleshostmortalityfromtheactionofepibionts.Third,thereislikelytobelittleornoimmunedefenseofthehostagainstepibionts.Allofthesefactorsaredi erentforendoparasites,whichareuna ectedbyhostmoltingbutareaf-fectedbytheimmuneresponseofthehostandmaybevirulentforthehost.Tomyknowledge,nostudyhasyetdemonstratedparasitecompetitioninplanktonhosts. 9.5 ConclusionsandOpenQuestionsItseemsratherclearthatparasiteshavethepo-tentialtoinuencehost populationdynamics andcommunitiesandthatinterspeciccompetitionandecologicalfactorsa ectingthehostinuenceparasitecommunities.Whatwearelackingaregeneralpatternsthatwouldallowustomakepre-dictionsforsystemswehavenotyetstudied.Forthis,weneedtostudynotonespeciesoronecom-munityatatimebutseveralinparallel.Anumberofissueshavenotyetbeenaddressedregardingplanktonparasites.HereIsuggestafewquestionsforfurtherresearch: 1. Someparasitesmayaltertheoutcomeofhostcompetition.Whichpropertiesofaparasitea ecthostcompetition,andwhichdonot? 2. Isthereinterspeciccompetitionamongen-doparasitesinplanktonhosts? 3. Arethere trade-o s betweencompetitionatdi erentlevels?Forexample,aparasitemightbeagoodcompetitoronahostbutispoorindispersalamonghostsoramong populations . 4. Doevolutionaryprocesses(e.g.,clonal selec-tion )inuencecommunityaspects? Chapter10ExperimentswithDaphniaandParasites ThischapterdescribeshowtousetheDaphniaparasitesystemforexperiments.Irstdiscusstheadvantagesofthesystemforresearchandeducation.ThenIdescribeanumberofexperiments,someofwhichareverysimpleandaresuitableforcoursesinexperimentalparasitologyandecology.Theexperimentsectionhastwoparts.Therstdiscussesexperimentsinwhichtheindividualhostistheunitofreplication.Suchexperimentscanbeusedtoaskquestionssuchas:Howdoesaparasitea ectitshost?Howisaparasitetransmitted?Thenextpartexpandstodiscussexperimentsthatuseentirepopulationsastheunitofreplication.HereIsuggestexperimentsthatposequestionssuchas:Doesaparasiteinuencehostdensity?Canaparasitedriveitshostpopulationtoextinction?Howquicklycanhostsevolveresistance? 10.1 AdvantagesofUsingtheDaphnia–ParasiteSystemforExperimentsTheDaphnia– parasite systemisparticularlysuit-ablefortestinghypothesesbecauseitallowsforthecreationofrathersimpleexperiments.Amongtheadvantagesofthissystemare:  Underlaboratoryconditions(20C),Daphniaproducetheirrsteggsafter7-15days(de-pendingonthefoodlevel).Thisequalstheshortestpossiblegenerationtimeinexperi-ments.Thereafter,theyproduceaclutchofparthenogeneticeggsevery3-4daysuntildeath,whichresultsinanapproximatelycon-stantfecundityacrosstheadultlifespan.Therstclutchisusuallysmallerthanthefollow-ingclutches.Onlyverylowfoodlevelsmayresultinskippedclutches.  Controlledconditionsallowotherextrinsicsourcesofmortality,e.g.,predationbysh,infectionbyotherparasites,tobeexcluded.  Parthenogeneticreproductionallowsthefe-malestoremainisolated(1femalein30-200mlofculturemedium)sothatfecundityanddeathschedulescanberecordedaccurately.Fromthese,birthanddeathratescanbecal-culatedintheabsenceofdensitydependence.Individualfemalescanbekeptwithorwith-outparasites.  Parthenogeneticreproductionfurtherallowsfortheseparationofgenetic(among-clonevariancecomponents)andnongenetice ects(within-clonevariancecomponents).  ManyDaphniaparasitestthedenitionthatepidemiologicalmodelsusefor micropara-sites verywell:small,unicellularparasitesthatreproducedirectlywithintheirhostsandare 10.3ExperimentswithIndividuals81 oftransmissionstagesfromthetreatmentsuspen-sion.ItmayalsolacknutritionalmaterialfortheDaphniathatthetreatmentsuspensionmaycon-tain.Second,theplacebomayhavesomee ectonthecontrols.Thise ect,oftencalledaplaceboe ect,describesadi erencebetweentheplacebotreat-mentandatotallyuntreatedcontrol.Ifthee ectoftheactualtreatmentandthee ectoftheplacebotreatmentdonotinuenceeachother,thisisnotaproblem,butifthee ectoftheplacebointer-actswiththee ectoftheactualtreatment,there-sultsmaybediculttointerpret.Forexample,supposeyoutestfortheimmuneresponseofahostafteritisexposedto parasite spores .Ifboththeplaceboandsporesuspensionscontaincom-poundsthatinuencetheimmuneresponseofthehost(e.g.,certainbacteria),oneobtainsestimatesofhostresponse,whichhavetobeseenwithinthelightofthissuspension.Awatercontrolmaynothavethesamee ect.Theresponsetotheex-posuretosporesmayhavebeendi erentifthesporeshadbeeninawatersuspensionwithoutanyothercompounds.Irecommend,therefore,us-ingtwocontrolsinindividual-levelexperiments:aplacebocontrolandacontrolwithoutanything.Youmaynotbeabletoavoidaplaceboe ect,butitisimportanttoknowaboutit. 10.2.1 UninfectedControlsinParasiteStudiesControlshavemorefunctionsthanjustbeingthesampleagainstwhichthetreatmentistested.Whentestingforthee ectofcertaintreatmentsona par-asite's performance,infectedhostsshouldbekeptunderdi erenttreatmentconditions(e.g.,parasitegrowthunderdi erentenvironmentalconditions; transmission ratesunderdi erentdensities).Be-causealltreatmentgroupsareinfected,anunin-fectedcontroldoesnotseemnecessary.Therearereasonswhyuninfectedcontrols(actuallyplacebo-exposedcontrols)shouldbeincluded.First,theuninfectedcontrolsallowyoutoverifythatallma-terialwasuninfectedbeforethestartoftheexperi-ment.Second,someexperimentsfailforunknownreasons,e.g.,theremaybehighunexplainedmor-tality.Thecontrolsallowyoutojudgewhethertheparasitesplayedaroleintheseresults. 10.2.2 UsingAdditionalTreatmentsasaQualityControlIncertainexperiments,itisnotclearwhetherthetreatmentappliedwillshowanye ect.Anegativeresultisdiculttopresentinaconvincingway,becausethenonsignicanceofthetreatmentsmayhavebeencausedbyotherreasonsthantheab-senceofane ect—theabsenceofevidenceisnotevidenceforabsence.Forexample,statisticalnoisemaydisguiseatreatmente ectinapoorlyexe-cutedexperiment.Toascertainthequalityoftheexperiment,Irecommendusinganadditionalfac-torthatisknowntoproduceavisiblee ect,evenifthise ectisnotthefocusofyourresearchques-tion.Forexample,onemayusetwofoodlevels,alongwiththeothertreatment.Thenifafoodef-fectisapparent,youmayconvincetheobserverthatothertreatmente ectscouldalsobefound,providedtheyarethere.Ifyoufailtondafoode ect,yourexperimentmayhavebeenpoorlyper-formed. 10.3 ExperimentswithIndividualsAnumberofDaphnia parasites caneasilybebredunderlaboratoryconditionsandarethereforesuit-ableforexperimentalwork.Theseexperimentscanbeconductedincoursesonthe evolution andecol-ogyofhost–parasiteinteractionsbutalsoforre-searchpurposes.Whatfollowsaresomesugges-tionsforsimpleexperimentsthatwillworkevenifonehaslittleexperiencewithDaphniaparasites. 10.3.1 E ectsofExposureDoseonParasiteandHostSuccessThe transmission stagesofhorizontallytransmit-ted parasites maybeadministeredtothehostindi erentconcentrations.Typically,higherdosesaremorelikelytoproduceinfections( Ebertetal.2000b ; Regoesetal.2003 ).Toquantifytheinfectionsuccessofparasiteisolates,astandardizedmea-sureisused:the ID50 (or infectivedose50% ),whichisthedoseatwhich50%oftheexposedhostsbe-comeinfected.TheID50mayvarystronglyamongparasiteisolatesandhostclones( Ebert1998b ).Itisusuallyestimatedwithastatisticalprocedure 86Glossary thespecies'interactionwithoneanother.Co-evolutioncanoccuramongmutualistsandhost–parasitepairs,aswellasamongen-tiregroupsofinteractingorganisms(e.g.,pollinator–plantsystems). CrustaceaAquaticarthropodscharacterizedbythepresenceofbiramousappendagesandtwosetsofantennae.Examplesincludecrabs,lob-sters,copepods,barnacles,shrimps,andwa-tereas. CyclicalparthenogenesisModeofreproductioninwhichphasesofparthenogenetic(asex-ual)andsexualreproductionalternate.Sev-eralasexualgenerationsmayfollowasexualgeneration.FoundinCladocera,Rotifera,andaphids. CyclomorphosisSeasonalchangeinphenotypeofmanyplanktonspecies.Forexample,someDaphniaspeciesproducespinestoprotectthemselvesagainstpredatorsduringthesum-merseason. DemePopulationthatissucientlyisolatedsothatitcanbeconsideredanevolvingunit.Demeismoretypicallyusedbyevolutionarybiologists. DensitydependenceIndicatesthattheintensityofaprocessdependsonthedensityofapopu-lation.Whenfecundityorindividualsurvivalinapopulationarenegativelydependentondensity(e.g.,parasite-inducedhostmortality),theprocesscouldpotentiallyregulatepop-ulationdensity.Transmissionofhorizontallytransmittedparasitesisusuallyhostdensitydependent. DepthselectionbehaviorBehaviorbywhichthezooplanktonmaintainsaparticularverticaldistributioninrelationtothestraticationofthewater(light,temperature,food,predationpressure).SeealsoDVM. DiapauseRestingperiodduringunfavorablecon-ditions,e.g.,duringwinterfreezingorduringdraughts. Dielverticalmigration(DVM)Specialcaseofdepthselectionbehaviorinwhichthepre-ferreddepthchangesinadiel(daily)pattern. Dosee ectAchangeinresponsetoexposuretosomeagentattributabletoachangeinthatagent'sconcentration.Forexample,thein-creaseinvirulenceorinfectionriskforhostsduringexposuretoincreasingparasitesporedoses. ElectrophoresisMethodtostudythemovementofchargedmoleculesinsolutioninanelec-tricaleld.Thesolutionisgenerallyheldinaporoussupportmediumsuchascelluloseacetateoragelmadeofstarch,agar,orpoly-acrylamide.Electrophoresisisgenerallyusedtoseparatemoleculesfromamixturebasedupondi erencesinnetelectricalchargeandalsobysizeorgeometryofthemolecules,de-pendentuponthecharacteristicsofthegelma-trix. EndemicPermanentpresenceofaparasitepop-ulationinahostpopulation.CompareEpi-demic. EndoparasiteSymbiontslocatedwithinthebodyofthehost.Theymaybeintra-orextracellular. Ephippium(pluralephippia)1.Membranousex-ternalwallssurroundingtherestingeggs(usuallysexualeggs)ofCladocera.2.RestingstageofCladoceraconsistingofoneortworestingeggs,surroundedbyamembranousexternalwall. EpibiontOrganismthatlivesattachedtothebodysurfaceofanotherorganism.Sometimesregardedasecto-parasites.Inzooplankton,epibiontsareoftenciliates,algae,bacteria,andfungi. EpidemicSudden,rapidspreadorincreaseintheprevalenceorintensityofaninfection.Com-pareEndemic. EpidemiologyStudyofinfectiousdiseasesanddisease-causingagentsonthepopulationlevelinaparasitologicalcontext.Itseekstochar-acterizethedisease'spatternsofdistributionandprevalenceandthefactorsresponsibleforthesepatterns.Inamoreappliedcontext,italsostrivestoidentifyandtestpreventionandtreatmentmeasures. EvolutionChangesinallelefrequenciesovertime. 88Glossary andshortgenerationtimes.Thekeyepidemi-ologicalvariable,bycontrastwithmacropara-sites,iswhethertheindividualhostisinfected. MicrosatellitelocusPlaceinthegenomewhereashortstringofnucleotides,usuallytwotovebaseslong,isrepeatedintandem.Thenumberofrepeatsatanygivenlocusisusuallyhighlyvariable(manyalleles)inapopulationandcanbeusedforDNAngerprinting. MorbidityStateofill-healthproducedbyadis-ease.Includesaspectsofreducedfecundity,lethargy,andothersignsofdisease. MultipleinfectionsInfectioninwhichanindivid-ualisinfectedbyparasitesofmorethanonespeciesormorethanonegenotypeofthesamespecies. ParasiterichnessSeeRichness. Parasite1.Disease-causingorganism.2.Organ-ismexhibitinganobligatory,detrimentalde-pendenceonanotherorganism(itshost).Con-ceptually,parasiteandpathogenarethesame.Endoparasitesliveinthehost'sinterior(Theymaybeintra-orextracellular).Ectoparasitesliveonthesurfaceofthehost. ParthenogenesisDevelopmentofanorganismfromanunfertilizedegg.Seealsocyclicparthenogenesis. PathogenDisease-causingmicroorganism,suchasviruses,bacteria,andprotozoa.Inthecon-textofthisbook,equivalenttoparasite. PhenotypicplasticityPhenotypicvariationex-pressedbyasinglegenotypeindi erentenvi-ronments. PhototacticbehaviorBehaviorthatisexpressedinthepresenceoflightstimuli. PhyllopodaOrderofEntomostracaincludingalargenumberofspecies,mostofwhichliveinfreshwater.Theyhaveattenedorleaf-likelegs,oftenverynumerous,whichtheyuseforswimming.AlsocalledBranchiopoda. PopulationdynamicsChangesinthepopula-tionsizethroughtime.Alsousedtodescribechangeinthedemographicstructureofthepopulation(sexratio,ageandsizestructure,etc.). PopulationGroupofinterbreedingindividualsandtheiro spring.Inasexualspecies,thisdef-initioncannotbeapplied;inthiscase,apop-ulationisagroupofphenotypicallymatchingindividualslivinginthesamearea. Populationgrowthrate(Malthusiangrowthrate,r)Measureofpopulationgrowth.Theinstan-taneousrateofincreaseofapopulationorgenotype.Itisusedasameasureoftness. Predator-induceddefenseDefensereactionofpreytriggeredbythepresenceoractionofapredatorsoastoreducetheexpecteddamageofthepredator. PredatorAnanimalthatkillsitsvictim,thepreyitem,andthenfeedsonittosubsistuntilthenextkill. PrepatentphaseInhelminthinfections,timepe-riodfrominfectionuntilafemalestartstopro-duceeggs.Itisequivalenttothelatentperiodinmicroparasiticinfections. PrevalenceProportionofhostindividualsin-fectedwithaparticularparasite.Oftenex-pressedasapercentage.Ameasureofhowwidespreadaninfectionordiseaseinahostpopulationis.Sometimesusedtoindicatetheproportionofinfectedhostsinasamplewithanyparasitespecies.Inmanystudies,preva-lenceismeasuredonlyinacertainfractionofhosts.Inzooplanktonstudies,oftenonlyadulthostsoradultfemalesareconsidered.Prevalenceisusuallyunderestimatedineldsamplesbecausenewinfectionsmayescapedetectionbytheinvestigator. PrimipareFemaleproducingo springoreggsforthersttime. proPOsystem(prophenol-oxidasesystem)TheproPOactivatingsystemplaysseveralfunc-tionsininvertebrateimmunityandisconsid-eredoneofthemostimportantdefensemech-anisms.Theoxireductasephenoloxidase(PO)ispartofacomplexsystemofproteinases,patternrecognitionproteins,andproteinaseinhibitorsthatconstitutetheproPOactivating 93 DaphniamagnaStraus.PhilosTransRSocLondSerB351:1689–1701 EbertD,HerreEA(1996)Theevolutionofparasiticdiseases.ParasitolToday12:96–100 EbertD,HamiltonWD(1996)Sexagainstvir-ulence:Thecoevolutionofparasiticdiseases.TrendsEcolEvol11:79–81 EbertD,PayneRJH,WeisserWW(1997)TheepidemiologyofparasiticdiseasesinDaphnia.InDettnerK,BauerG,VölklW(eds.)Ver-ticalfoodwebinteractions:Evolutionarypat-ternsanddrivingforces,pp91–111,Heidelberg:Springer EbertD,ManginKL(1997)Theinuenceofhostdemographyontheevolutionofvirulenceofamicrosporidiangutparasite.Evolution51:1828–1837 EbertD(1998a)Experimentalevolutionofpara-sites.Science282:1432–1435 EbertD(1998b)Infectivity,multipleinfections,andthegeneticcorrelationbetweenwithin-hostgrowthandparasitevirulence:AreplytoHochberg.Evolution52:1869–1871 EbertD,Zschokke-RohringerCD,CariusHJ(1998)Withinandbetweenpopulationvariationforre-sistanceofDaphniamagnatothebacterialen-doparasitePasteuriaramosa.ProcRSocLondBBiolSci265:2127–2134 EbertD(1999)Theevolutionandexpressionofpar-asitevirulence.InStearnsSC(ed.)Evolutioninhealthanddisease,pp161–172,Oxford:OxfordUniversityPress EbertD,Zschokke-RohringerCD,CariusHJ(2000a)Dosee ectsanddensity-dependentreg-ulationoftwomicroparasitesofDaphniamagna.Oecologia122:200–209 EbertD,LipsitchM,ManginKL(2000b)Thee ectofparasitesonhostpopulationdensityandex-tinction:ExperimentalepidemiologywithDaph-niaandsixmicroparasites.AmNat156:459–477 EbertD,HottingerJW,PajunenVI(2001)TemporalandspatialdynamicsofparasitesinaDaphniametapopulation:Whichfactorsexplainparasiterichness?Ecology82:3417–3434 EbertD,BullJJ(2003)Challengingthetrade-o modelfortheevolutionofvirulence:Isvirulencemanagementfeasible?TrendsMicrobiol11:15–20 EbertD,CariusHJ,LittleT,DecaesteckerE(2004)Theevolutionofvirulencewhenparasitescausehostcastrationandgigantism.AmNat164:S19–S32 FelsD,LeeVA,EbertD(2004)Theimpactofmi-croparasitesontheverticaldistributionofDaph-niamagna.ArchHydrobiol161:65–80 FelsD(2005)Thee ectoffoodonmicropara-sitetransmissioninthewatereaDaphniamagna.Oikos109:360–366 FelsensteinJ(1985)Phylogeniesandthecompara-tivemethod.AmNat125:1–15 FinlaysonLH(1949)MortalityofLaemophloeus(Coleoptera,Cucujidae)infectedwithMattesiadisporaNaville(Protozoa,Schizogregarinaria).Parasitology40:261–264 FitzsimmonsJM,InnesDJ(2005)NoevidenceofWolbachiaamongGreatLakesareapopulationsofDaphniapulex(Crustacea:Cladocera).JPlank-tonRes27:121–124 FlemingSB,Kalmako J,ArchibaldRD,StewartKM(1986)Densitydependent-virusmortalityinpopulationsofWisecana(Lepidoptera:Hep-ialidae).JInvertPathol48:193–198 FranceRL,GrahamL(1985)Increasedmi-crosporidianparasitismofthecrayshOr-conectesvirilisinanexperimentallyacidiedlake.WaterAirSoilPollut26:129–136 FreemanS,HerronJC(2001)EvolutionaryAnaly-sis.NewJersey,USA,PrenticeHall,2ndedn. FreyerG(1991)FunctionalmorphologyandtheadaptiveradiationoftheDaphniidae(Bran-chiopoda:Anomopoda).PhilosTransRSoc331:1–99 FriedrichC,WinderO,SchaerK,ReinthalerFF(1996)LightandelectronmicroscopestudyonGurleyadaphniaesp.nov.(Microspora,Gur-leyidae),aparasiteofDaphniapulex(Crustacea,Phyllopoda).EurJProtistol32:116–122 96References MargolisL,EschGW,HolmesJC,KurisAM,SchadGA(1982)Theuseofecologicaltermsinpara-sitology.JParasitol68:131–133. MayRM(1974)Stabilityandcomplexityinmodelecosystems.Princeton(NJ):PrincetonUniversityPress MayRM,AndersonRM(1978)Regulationandsta-bilityofhost-parasitepopulationinteractions.II.Destabilizingprocesses.JAnimEcol47:249–268 MayRM,AndersonRM(1979)Populationbiologyofinfectiousdiseases:PartII.Nature280:455–461 MayRM,AndersonRM(1983)Epidemiologyandgeneticsinthecoevolutionofparasitesandhosts.ProcRSocLondBBiolSci219:281–313 McCallumH,DobsonA(1995)Detectingdiseaseandparasitethreatstoendangeredspeciesandecosystems.TrendsEcolEvol10:190–194 Metchniko E(1884)UebereineSprosspilzkrank-heitderDaphniden.BeitragzurLehreüberdenKampfderPhagocytengegenKrankheitserre-ger.VirchowsArchPatholAnatPhysiol96:177–193 Metchniko E(1888)Pasteuriaramosaunrepresen-tantdesbacteriesàdivisionlongitudinale.AnnInstPasteurParis2:165–170 Metchniko E(1889)Contributionsàl'étudedupléomorphismedesbactériens.AnnInstPasteurParis3:61–68 MinchellaDJ,LoverdePT(1981)Acostofincreasedearlyreproductivee ortinthesnailBiomphalariaglabrata.AmNat118:876–881 MinchellaDJ(1985)Hostlife-historyvariationinresponsetoparasitism.Parasitology90:205–216 MiracleMR(1977)Epidemiologyinrotifers.ArchHydrobiolBeihErgebnLimnol8:138–141 MitchellSE,ReadAF,LittleTJ(2004)Thee ectofapathogenepidemiconthegeneticstructureandreproductivestrategyofthecrustaceanDaphniamagna.EcolLett7:848–858 MitchellSE,RogersES,LittleTJ,ReadAF(2005)Host-parasiteandgenotypebyenvironmentin-teractions:temperaturemodiespotentialforse-lectionbysterilisingpathogen.Evolution MooreJ(2002)Parasitesandthebehaviorofani-mals.Oxford:UniversityPress MorandS,ManningSD,WoolhouseMEJ(1996)Parasite-hostcoevolutionandgeographicpat-ternsofparasiteinfectivityandhostsusceptibil-ity.ProcRSocLondBBiolSci263:119–128 MucklowPT,EbertD(2003)ThephysiologyofimmunityinthewatereaDaphniamagna:Envi-ronmentalandgeneticaspectsofphenoloxidaseactivity.PhysiolBiochemZool76:836–842 MucklowPT,VizosoDB,JensenKH,RefardtD,EbertD(2004)Variationforphenoloxidaseactiv-ityanditsrelationtoparasiteresistancewithinandbetweenpopulationsofDaphniamagna.ProcRSocLondBBiolSci271:1175–1183 ParkT(1948)Experimentalstudiesoninterspeciescompetition.I.Competitionbetweenpopula-tionsoftheourbeetlesTrifoliumconfusum(Duval)andTriboliumcansteneum(Herbst).EcolMonogr18:265–307 PetersRH,BernardiRD(1987)Daphnia.Memoriedell'IstitutoItalianodiIdrobiologia54:1–502 PoulinR(1998)Evolutionaryecologyofparasites.London:ChapmanandHall PrestonJF,DicksonDW,MaruniakJE,NongG,BritoJA,SchmidtLM,Giblin-DavisRM(2003)Pasteuriaspp.:Systematicsandphylogenyofthesebacterialparasitesofphytopathogenicne-matodes.JNematol35:198–207 PricePW(1980)Evolutionarybiologyofpara-sitism.Princeton:PrincetonUniversityPress ProwseGA(1954)Aphamomycesdaphniaes.nov.,parasiticonDaphniahyalina.TransBrMycolSoc37:22–28 PulkkinenK,EbertD(2004)Hoststarvationde-creasesparasiteloadandmeanhostsizeinex-perimentalpopulations.Ecology85:823–833

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