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Origin of Species Galapagos Tortoise. Origin of Species patterns of speciation Anagenesis Anagenesis –A single population is transformed enough to be.

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Presentation on theme: "Origin of Species Galapagos Tortoise. Origin of Species patterns of speciation Anagenesis Anagenesis –A single population is transformed enough to be."— Presentation transcript:

1 Origin of Species Galapagos Tortoise

2 Origin of Species patterns of speciation Anagenesis Anagenesis –A single population is transformed enough to be designated a new species Cladogenesis Cladogenesis –Branching evolution. A new species arises from a small population that “Buds” from a parent species. –Most species probably evolved this way. The branching evolution is the basis of biological diversity

3 Two patterns of speciation

4 Origin of Species Species definitions Biological species = a population whose members have the potential to interbreed with one another and produce viable, fertile offspring, but who cannot produce viable, fertile offspring with members of another species. (Reproductive Isolation) Biological species = a population whose members have the potential to interbreed with one another and produce viable, fertile offspring, but who cannot produce viable, fertile offspring with members of another species. (Reproductive Isolation) –The biological species concept cannot be applied to asexually reproducing organisms Morphospecies = species defined by their anatomical features Morphospecies = species defined by their anatomical features

5 The biological species concept is based on interfertility rather than physical similarity Eastern Meadowlark Western Meadowlark

6 Reproductive barriers Any factor that impedes two species from producing fertile hybrids Any factor that impedes two species from producing fertile hybrids Prevents interbreeding between closely related species Prevents interbreeding between closely related species Prezygotic barriers (impedes mating or hinders ova fertilization) Prezygotic barriers (impedes mating or hinders ova fertilization) Postzygotic barriers (after fertilization) Postzygotic barriers (after fertilization)

7 Origin of Species Prezygotic barriers 1. Habitat isolation 2. Temporal isolation 3. Behavioral isolation 4. Mechanical isolation 5. Gametic isolation

8 Habitat Isolation

9 Temporal Isolation Late-winter mating seasonSummer mating season

10 Blue-footed boobies … Courtship ritual as a behavioral barrier between species.

11 Mechanical Isolation “You can’t fit a square peg in a round hole” Gametic Isolation “gamete recognition”

12 Origin of Species Postzygotic barriers 1. Reduced hybrid viability (vigor) 2. Reduced hybrid fertility 3. Hybrid breakdown

13 Origin of Species Introgression The transplantation of alleles between species. Alleles occasionally “seep” through all reproductive barriers and pass between gene pools of closely related species. May occur when a fertile hybrid mates successfully with one of the parent species.

14 Liger Female Ligers are fertile and can reproduce. If a Female liger mated with a male tiger the offspring would have some lion genes. If that offspring could then mate with a tiger the lion genes would continue on within the Tiger Gene Pool, an example of introgression. Female Ligers are fertile and can reproduce. If a Female liger mated with a male tiger the offspring would have some lion genes. If that offspring could then mate with a tiger the lion genes would continue on within the Tiger Gene Pool, an example of introgression. Hercules the liger

15 A summary of reproductive barriers between closely related species

16 Origin of Species Modes of speciation Allopatric speciation Allopatric speciation –A population forms a new species while geographically isolated from its parent population Sympatric speciation Sympatric speciation –Species formation occurs in geographically overlapping populations

17 Two modes of speciation

18 Origin of Species Allopatric speciation –occurs when the initial block to gene flow is a geographical barrier that physically isolates the population. –The genetically isolated group can then follow its own evolutionary course as changes in allele frequencies occur and are undiluted by gene flow from other populations

19 Has speciation occurred during geographic isolation? Has speciation occurred during geographic isolation?

20 Allopatric speciation of squirrels in the Grand Canyon Harris’s antelope squirrel (south rim) White-tailed antelope squirrel (north rim)

21 Speciation in Galapagos Finches

22 Speciation in Cichlids

23 Origin of Species Allopatric speciation Adaptive Radiation = emergence of numerous species from a common ancestor introduced into an environment. Example: Darwin’s finches on the Galapagos island chain

24 Adaptive Radiation of Galapagos Finches

25 A model for adaptive radiation on island chains A model for adaptive radiation on island chains

26 Adaptive Radiation in Cichlids (Specialization in feeding)

27 Origin of Species Sympatric speciation Formation of a new species within the geographical range of the parent population (no geographical isolation) Can occur quickly (in one generation) if a genetic change results in a reproductive barrier between mutants and the parent population

28 Origin of Species Sympatric speciation Polyploid speciation Many plant species have originated from improper cell division that resulted in polypoidy Many plant species have originated from improper cell division that resulted in polypoidy –Autopolyploidy – an organism that has more than two chromosome sets, all derived from the same species –Allopolyploidy – a polyploid hybrid resulting from contributions by two different species. More common than autopolyploidy. Hybrids are usually sterile but may be very vigorous and propagate asexually. Iris Daylily

29 Sympatric speciation by autopolyploidy in plants Sympatric speciation by autopolyploidy in plants

30 One mechanism for allopolyploid speciation in plants One mechanism for allopolyploid speciation in plants

31 Punctuated Equilibrium vs. Gradualism Punctuated equilibrium model suggests evolution occurring in spurts of relatively rapid change instead of gradual divergence Punctuated equilibrium model suggests evolution occurring in spurts of relatively rapid change instead of gradual divergence

32 Two models for the tempo of speciation Two models for the tempo of speciation


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