Question What is a species Evolution theory must also explain how species originate Darwins Mystery of mysteries In the Galápagos Islands Darwin discovered plants and animals found nowhere else on Earth ID: 678144
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Slide1
Chapter 24
The Origin of SpeciesSlide2
Question?
What is a species?
Evolution
theory must also explain how species originate.
Darwin’s “Mystery of mysteries
”
In the Galápagos Islands Darwin discovered plants and animals found nowhere else on EarthSlide3
Overview: That “Mystery of Mysteries”
Speciation
, the origin of new species, is at the focal point of evolutionary theory
Evolutionary theory must explain how new species originate and how populations
evolveSlide4
Fig. 24-1
How did this flightless bird come to live on the isolated Gal
á
pagos Islands?Slide5
Microevolution
consists of adaptations that evolve within a population, confined to one gene pool
Macroevolution
refers to evolutionary change above the species
level
Example – the appearance of feathers during the evolution of birds from one group of dinosaursSlide6
Two Basic Patterns of Evolutionary Change”
1.
Anagenesis
ana
= new,
genos
= race
Accumulation of heritable changes that gradually transforms a species into a species with different characteristicsSlide7
Two Basic Patterns of Evolutionary Change”
2.
Cladogenesis
klados
= branch,
genos
= race
Branching evolution in which a new species arises from a population that buds from a parent speciesSlide8
Concept 24.1: The biological species concept emphasizes reproductive isolation
Species
is a Latin word meaning “kind” or “appearance”
Biologists compare morphology, physiology, biochemistry, and DNA sequences when grouping organismsSlide9
Fig. 24-2a
Similarity between different speciesSlide10
Fig. 24-2b
(b) Diversity within a species
Diversity within a speciesSlide11
Question
How many species of African Violets are here?Slide12
The Biological Species Concept
The
biological species concept
states that a
species
is a group of populations whose members have the potential to interbreed in nature and produce viable, fertile offspring; they do not breed successfully with other populations
Gene flow between populations holds the phenotype of a population togetherSlide13
Fig. 24-3c
Grey-crowned babblers
Does gene flow occur between widely separated populations?Slide14
Reproductive Isolation
Reproductive isolation
is the existence of biological factors (barriers) that impede two species from producing viable, fertile offspring
Hybrids
are the offspring of crosses between different species
Reproductive isolation can be classified by whether factors act before or after fertilizationSlide15
Prezygotic
barriers
block fertilization from occurring by:
Impeding different species from attempting to mate
Preventing the successful completion of mating
Hindering fertilization if mating is successfulSlide16
Postzygotic
barriers
prevent the hybrid zygote from developing into a viable, fertile adult:
Reduced hybrid viability
Reduced hybrid fertility
Hybrid breakdownSlide17
EXAMPLES OF
Prezygotic
BarriersSlide18
Habitat isolation
: Two species encounter each other rarely, or not at all, because they occupy different habitats, even though not isolated by physical barriers
Terrestrial
Thamnophis
Water-dwelling
ThamnophisSlide19
Habitat Isolation
Populations live in different habitats or ecological niches.
Ex – mountains
vs
lowlands.Slide20
Temporal isolation
: Species that breed at different times of the day, different seasons, or different years cannot mix their gametes
Eastern spotted skunk
(
Spilogale
putorius
)
Western spotted skunk
(
Spilogale
gracilis
)Slide21
Temporal Isolation
Breeding seasons or time of day different.
Ex – flowers open in morning or evening.Slide22
Behavioral isolation
: Courtship rituals and other behaviors unique to a species are effective barriers
Courtship ritual of blue-
footed boobiesSlide23
Behavioral Isolation
Mating or courtship behaviors different.
Different sexual attractions operating.
Ex – songs and dances in birds.Slide24
Mechanical isolation
: Morphological differences can prevent successful mating
Bradybaena
with shells spiraling
in opposite directionsSlide25
Mechanical Isolation
Structural differences that prevent gamete transfer.
Ex – anthers not positioned to put pollen on a bee, but will put pollen on a bird.Slide26
Gametic
isolation
: Sperm of one species may not be able to fertilize eggs of another species
Sea
urchinsSlide27
Gametic Isolation
Gametes fail to attract each other and fuse.
Ex – chemical markers on egg and sperm fail to match.Slide28
EXAMPLES OF
Postzygotic
BarriersSlide29
Reduced Hybrid Viability
Zygote fails to develop or mature.
Ex – when different species of frogs or salamanders hybridize.Slide30
Reduced hybrid viability
: Genes of the different parent species may interact and impair the hybrid’s development
Ensatina
hybridSlide31
Reduced hybrid fertility
: Even if hybrids are vigorous, they may be
sterile
Hybrids are viable, but can't reproduce sexually.
Chromosome count often “odd” so meiosis won’t work.
Ex – donkeys and horses produce mulesSlide32
Fig. 24-4m
(i)
Donkey
DonkeySlide33
Fig. 24-4n
(
j)
HorseSlide34
Fig. 24-4o
(k)
Mule (sterile hybrid)Slide35
Hybrids
‘Heaven Scent’
an F1 hybrid between 2 species, but sterile.Slide36
Hybrid Breakdown
Offspring are fertile, but can't compete as well as the “pure breeds”.
Ex – many plant hybridsSlide37
Hybrid breakdown
: Some first-generation hybrids are fertile, but when they mate with another species or with either parent species, offspring of the next generation are feeble or sterile
Hybrid cultivated rice plants with
stunted offspring (center)Slide38
Limitations of the Biological Species Concept
The biological species concept cannot be applied to fossils or asexual organisms (including all prokaryotes)Slide39
Other Definitions of Species
Other species concepts emphasize the unity within a species rather than the separateness of different species
The
morphological species concept
defines a species by structural features
It applies to sexual and asexual species but relies on subjective criteriaSlide40
Morphospecies
Organisms with very similar morphology or physical form.Slide41
Problem
Where does extensive phenotype variation fit?Slide42
The
ecological species concept
views a species in terms of its ecological niche
It applies to sexual and asexual species and emphasizes the role of disruptive selection
The
phylogenetic
species concept
: defines a species as the smallest group of individuals on a
phylogenetic
tree
It applies to sexual and asexual species, but it can be difficult to determine the degree of difference required for separate speciesSlide43
Question
How many species of African Violets are here?Slide44
African Violets
1950-60’s –20 species described
70,000 cultivars or human created hybridsSlide45
African Violets
2007 – lumping occurred to 6 species and 10 subspecies
2008 – AVSA now recognizes 9 species and 8 subspecies
point
– species definitions can be fluid and changeSlide46