11. Macroevolution

11. Macroevolution - Macroevolution Macroevolution Ideas...

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Macroevolution Macroevolution - Ideas about how species arise and diversify - Historical, unites paleontology and population biology - Patterns of species distributions in time and space o Speciation: appearance of new species o Extinctions: complete disappearance of species Definition of species - Must account for: o Distinctiveness of species at a location o Connection of different populations of a species - Biological Species concept: o One or more population (s) of individuals that interbreed under natural conditions to produce fertile offspring Criteria for species - Interbreeding must produce fertile offspring: o Horse + donkey -> mule (infertile) - Interbreeding must occur under natural circumstances: o Dog + coyote -> coydog (fertile) o Usually do not occur in natural populations The beginning of species: speciation - Gene flow maintains similarities among populations of a species - For speciation to occur gene flow must be blocked - No gene flow -> divergence -> reproductive isolation - Modes of reproductive isolation:
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o Prezygotic -> before fertilization o Postzygotic -> after fertilization Reproductive isolation (figure 22.1) Barriers to reproduction Pre-zygotic post-zygotic Species A + Species B -> Mating -> Fertilization -> Offspring Habitat, behavioral isolation / mechanical, gametic isolation/hybrid breakdown, reduced hybrid viability, sterility The geography of speciation - Speciatiion occurs readily in the absence of gene flow - Allopatric speciation o Geographic barrier separates populations - Sympatric speciation o No geographic separation - Genetically separated populations can evolve reproductive isolating mechanisms Allopatric speciation (figure 22.8, 22.9) - Many ways to get geographic isolation over geologic time - Barriers to movement stop the flow of genes o Lakes rise and fall, mountains rise, rivers change course,
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11. Macroevolution - Macroevolution Macroevolution Ideas...

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