1 1 . Patterns of speciation and extinction
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1 1 . Patterns of speciation and extinction

The rise and fall of biodiversity. Four major mass extinctions of marine organisms:. End of Silurian Devonian, Permian, and Cretaceous). Rise in diversity during Cambrian, Silurian, Cretaceous, and Paleogene.

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1 1 . Patterns of speciation and extinction




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Slide1

11. Patterns of speciation and extinction

The rise and fall of biodiversity

Four major mass extinctions of marine organisms:

End of Silurian Devonian, Permian, and Cretaceous)Rise in diversity during Cambrian, Silurian, Cretaceous, and Paleogene

The rise and fall of biodiversity

Eliminating all groups known only from a single stage (5-6 mya):

Rise in diversity during

C

ambri

an

, and Ordovicium and in the Paleogene

Decline of longer lasting taxa from Ordovicium to Triassic

Slide2

What is a species in the evolutionary context?

The biological species concept states that species are actually or potentially interbreeding natural populations that are genetically isolated from othersThe evolutionary species concept states that species are ancestor – descendent lineages of organisms that have their own evolutionary fate. The phylogenetic species concept states that a species is the smallest monophyletic group of organisms of common ancestry (a lineage from one node to another).The genetic species concept states that a species is a genetically sufficiently distinct group of organisms as identified by a genetic fingerprint.The ecological species concept states that a species is a group of organisms (population) that are ecologically distinct from other groups. The heuristic species concept states that a species is a group of organisms that are practically clustered together for the aims of a certain study.

Corvus corax

Corvus corone

Corvus frugilegus

Slide3

Does any species concept fit?

Meteorus pulchricornis

from New Zealand

Salmonella typhi

Heliconius

butterflies

Dog races

Thelytokous waps

Presexual species

Morphologically divergent races

Genetical fingerprint „species”

Slide4

How do species emerge?

A classical example

Darwin finches,

Geospiza spp.)

1. Large cactus finch (Geospiza conirostris)

2. Large ground finch (Geospiza magnirostris)

3. Medium ground finch (Geospiza fortis)

4. Cactus finch (Geospiza scandens)

5. Sharp-beaked ground finch (Geospiza difficilis)

6. Small ground finch (Geospiza fuliginosa)

7. Woodpecker finch (Cactospiza pallida)

8. Vegetarian tree finch (Platyspiza crassirostris)

9. Medium tree finch (Camarhynchus pauper)

10. Large tree finch (Camarhynchus psittacula)

11. Small tree finch (Camarhynchus parvulus)

12. Warbler finch (Certhidia olivacea)

13. Mangrove finch (Cactospiza heliobates

Slide5

Speciation is the divergence of genetic structure between subpopulations until new separate populations emerge.

Any mechanism that promotes the emergence of sublineages is therefore a potential speciation mechanism

Premating examples are:spatial isolationbehavioural isolationtemporal isolation (separated generations)host switch in parasites and herbivoresselective habitat choice

Divergence can be triggered by premating and postmating mechanisms:Premating mechanisms are those that keep populations isolated before mating occurs.Postmating mechanisms prevent hybrids to develop or breed.

Postmating examples are:genetic incompatibilitymorphological incompatibilityearly death of hybridssterility

Basal population

Lineage A

Lineage B

Genetic distance

Slide6

Speciation due to ecological or spatial or temporal isolation

Barriers of gene flow or genetical isolation

Allopatric barrier

Ancestral population

Spatial barrier

Lineage A

Lineage B

Peripatric barrier

Ancestral population

Lineage A

Lineage B

Founder effect

Allopatric speciation

Peripatric speciation

Slide7

Sympatric lineage emergence

Ancestral population

Genetic differences within the same geographical region result in genetic isolation and lineage divergence.

Parapatric lineage emergence

Differential selection pressures cause lineage divergence even within narrow spatial ranges.

Ancestral population

Barriers of gene flow or genetic isolation

Sympatric speciation

Parapatric speciation

Slide8

How fast is speciation?

Lineage

length

Time to genetic isolation

It seems that evolutionary speed is not correlated with generation length

and body size

Are species reproductively independent lineages?

Many ‘species’ do not represent genetically isolated lineages. However ecological, morphological or spatial mating barriers exist

Time to ecological isolation

Slide9

Adaptation or species selection?

Morphological divergence

Time

Species selection

Morphological divergence

Time

Adaptive trend

Species selection means that evolution proceeds via differential extinction of species with certain characteristic features.

Adaptive trends imply differential speciation rates of better adapted lineages

.

Slide10

Examples of fast evolutionary speed

Cameraria ohridella

Minotetrastichus frontalis (=ecus)

The Faroer Island house mouse origin

at

ed from the Western European House Mouse (Mus domesticus). During 250 years of colonization it has evolved three distinct isolated island populations. The Nólsoy House Mouse is a sub-species called (Mus musculus faeroensis) and the Mykines House Mouse is also a sub-species called (Mus musculus mykinessiensis). Its closest relative was the now extinct St Kilda House Mouse (Mus musculus muralis).

The Aesculus miner C. ohridella was first described in 1984 in Albania as a rare new species.Since then it colonized whole Europe and became a dominant mining species on Aesculus hippocastanus.It is unknown what caused the rapid spread.Nevertheless it is a good example how an evolutionary novelty can trigger dispersion. This dispersion initiated host switches and lineage divergence of its major parasite Minotetrastichus frontalis.

Mus musculus

Slide11

Natura non facit saltus?

Species A

Species B

Species A

Species B

Species C

Time

Genetic divergence

Speciation event

Speciation event

Gradual speciation

Saltatorial speciation

Gradualism in Pliocene snails, 10 to 3 Mya.

Saltatorial speciation

means sudden rapid evolutionary change that is manifest in genetic isolation.

Stasis

Stasis

Slide12

The classic view of speciation

Phyletic gradualism asserts that Species arise by the transformation of an ancestral population into its modified descendants. The transformation is even and slow. The transformation involves large numbers, usually the entire ancestral population. The transformation occurs over all or a large part of the ancestral species' geographic range

This implies thatIdeally, the fossil record for the origin of a new species should consist of a long sequence of continuous, insensibly graded intermediate forms linking ancestor and descendant. Morphological breaks in a postulated phyletic sequence are due to imperfections in the geological record.

Ernst Mayr, 1904-2005

Classical Darwinian selection implies a continuous (graduate) change in species characters.

The combination with population genetics gave rise to the neodarwinean synthetic theory of evolution formulated mainly by Ernst Mayr and J.B.S. Haldane.

John B. S. Haldane, 1892-1964

Slide13

The theory of punctuated equilibrium of Niles Eldredge and Stephen Jay Gould states thatThe fossil record is relatively complete.Most speciation occurs via peripatric speciation. Widespread species usually change slowly, if at all, during their time of existence. Daughter species usually develop in a geographically limited region. Daughter species usually develop in a stratigraphically limited extent.Sampling of the fossil record will reveal a pattern of most species in stasis, with abrupt appearance of newly derived species being a consequence of ecological succession and dispersion. Adaptive change in lineages occurs mostly during periods of speciation. Trends in adaptation occur mostly through the mechanism of species selection.

Tempo and mode of evolution reconsidered

Stephen Jay Gould, 1941-2002

Niles Eldredge 1943-

Slide14

Time

Genetic distance

Speciation

Speciation

Speciation

Subspeciation

Stasis

Stasis

Stasis

Stasis

Evolution is assumed to proceed via fast genetic transitions within an peripatric speciation framework.

Punctuated equilibrium

Mean thorax width of Trilobite species

The evolution of man is a good example of punctuated equilibrium

.

Slide15

Does evolution need hopeful monsters? Or evolution above the species level

Richard Goldschmidt,1878-1958

Classical Darwinian theory assumes character evolution to be a gradual process.However higher taxa are of often distinguished without any intermediate fossils (fossil gaps).Did major evolutionary branches evolved very fast or is our fossil record too incomplete?

Goldschmidt assumed that major evolutionary transitions are caused by mutations in regulatory genes giving rise to major morphological changes.Most of these highly altered creatures have no chance to survive, but few succeed and are ‘hopeful monsters’ that are ancestors of new higher taxa.Punctuated equilibrium is a modern form of this saltationism.

Slide16

Ambulocetans natans

Dorudon atrox

Eocene

50 mya

40 mya

Paleocene

65 mya

Rhodocetus kasrani

The history of whales: Gradualism or saltationism?

46 mya

The history of birds: Gradualism or saltationism?

Protarchaeo-pteryx robusta

Jura

150mya

135 mya

Caudipteryx

zoui

Sinosauro-

pteryx prima

First feathers

Slide17

Evolutionary trends and major questions

Major evolutionary trends

Rising number of genes across clades?Rising morphological complexity across clades?Rising hierarchical organization?Rising physiological and ecological flexibility?Rising efficiacy in design?Rising evolvability (the ability to cope with changing environmental conditions)?Decreasing evolvability due to trends for specialization?Rising complexity of ecological interactions?

Evolutionary constraints

What made vertebrates prone to evolve large brains?Why did insects never get large?Why did plants never evolve nerves and muscles?Why did Dinosaurs not become small? Why did marine taxa stop evolving since the Cambrian?Why did major taxa (phyla) only evolve in the late Proterozoic? Did life appear only once?

Discuss these questions using the many internet sources!

Slide18

Extinctions

Trade off between extinction and speciation

The background extinction rate e(t) of marine taxa decreased!

Marine taxa

Slide19

Trade off between extinctions and speciations

Extinction and origination rates are connected.

Peaks in speciation of marine taxa occurred often after mass extinctions.

Mass extinctions might also change ecological dominance. Bivalvia raised after the mass extinction of the ecologically similar Brachiopoda.

Slide20

Mass extinctions are not equally distributed among taxa.

Advanced species that are physiologically more buffered against environmental changes increased in frequency after mass extinctions

Motile species were often less affected than sessile species

Predator species richness increased after mass extinctions

Slide21

Adaptation to herbivory and promiscuity might cause high rates of speciation

Cucujoidea

< 10000 species

Curculionoidea

> 200000 species

Trichoptera

< 10000 species

Lepidoptera

> 300000 species

Herbivory

Herbivory

Predators

Predators

Detritivorous

Manucodes

5 species

Birds of paradise

33 species

Hummingbirds

319 species

Promiscuity

Promiscuity

Pair bonds

Pair bonds

Change in feeding style

Change in mating system

Swifts

103 species

Slide22

The interplay between extinction and origination

Correlations between actual diversity and speciation r(D-

D

S) and extinction rates r(D-DE) (mid Jurassic to Neogene) show that high diversities were correlated with high extinction rates but not with high speciation rates. This points to a density dependent effect in speciation.

The

equilibrium number of species

is then

Hence, the realized number of species is always lower than the maximum possible number.

Ecological systems cannot be saturated with species.

Slide23

Data from Mc Peek, Brown (2007)

Species richn

e

ss increases with taxon age.Speciation rates l are independent of species richness but decrease with taxon age.Younger taxa have higher speciation rates l.Total species richness is also determined by species survival rates.

Chordata

Arthropoda

Mollusca

Species richness and taxon age

Insecta and Vertebrata

Slide24

Extinction rates seem to be pylogenetically clustered

From Roy et al. 2009)

Extinction rates of mesozoic Bivalvia were stable in time

Extinction rates were phylogenetically clustered in time

Slide25

The Red Queen hypothesis

Extinction rates (probabilities) are roughly constant through time.One explanation for this is the Red Queen hypothesis (after Lewis Carroll’s Through the Looking Glass).Each species has to run as far as possible (to evolve continuously) only to stay in the same place.Its competitors, predators and parasites also evolve continuously. Under these circumstances extinction probabilities will remain roughly constant.

Leigh M. Van Valen 1935-

Survival times for extinct genera of Echinoidea (sea urchins).

Slide26

Today’s reading:

Speciation:

http://en.wikipedia.org/wiki/Speciation

Observed instances of speciation:

http://www.talkorigins.org/faqs/faq-speciation.html

The origin of species:

http://bill.srnr.arizona.edu/classes/182/Lecture%202007-03.htm

Punctuated equilibrium:

http://en.wikipedia.org/wiki/Punctuated_equilibrium

Punctuated equilibrium:

http://www.mun.ca/biology/scarr/2900_Fossils.htm