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Allopatric Speciation—Drift

Allopatric Speciation—Drift. Drift is important in evolution Just because an allele is common doesn’t mean selection favored it. Speciation via drift? Probably not. Flies in allopatry , same environment never  RIM

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Allopatric Speciation—Drift

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  1. Allopatric Speciation—Drift • Drift is important in evolution • Just because an allele is common doesn’t mean selection favored it

  2. Speciation via drift?Probably not. • Flies in allopatry, same environment never  RIM • Drift may facilitate speciation, but probably cannot often cause speciation on its own

  3. Ecological Speciation • Sister species in the same lake • Big is benthic, small is limnetic • No interbreeding in nature– habitat isolation or pre-mating RIM?

  4. No-choice mating trials in the lab Low probability of spawning between different ecomorphs, even when closely related (A). Ecology is important in RIM. C = control (same species, same population, high probability of spawning) D = same ecotype, distantly related (act like same species) A = sympatric, closely related, different ecotype (act like different Biological species) B = allopatric, distantly related, different ecotype Reproductive compatibility determined more by ecotype than by genetic relatedness

  5. RIM appears to be body size—did divergent natural selection on body size  speciation?

  6. Speciation via Sexual Selection • Many sister lineages with same ecological niche, but different secondary sexual characters

  7. Greater species diversity in lineages with greater promiscuity. Due to stronger sexual selection?

  8. Fig. 24-12 Speciation by Sexual Selection EXPERIMENT Monochromatic orange light Normal light P. pundamilia P. nyererei Under manipulated lighting, females made “wrong” mate choice

  9. Genetics and Timing of Speciation

  10. Time to SpeciationVaries

  11. Fig. 24-19 One-gene speciation

  12. RIM’s can be generated by simple differences in genetics

  13. Ancestral species: Speciation may involve hybridization, so it can be quick for many species AA BB DD Wild T. tauschii (2n = 14) Triticum monococcum (2n = 14) Wild Triticum (2n = 14) Product: AA BB DD T. aestivum (bread wheat) (2n = 42)

  14. Speciation involves a stochastic element… • Medium ground finches on Daphne major (Gallapagos Island)

  15. Immigrant Geospizafortis: large body, wide beak, unusual song (bad mimicry) Immigrant F1 F6 F5 Top to bottom: A to F show successive generations of the hybrids, which now mate only with each other. Grant and Grant, PNAS, doi/10.1073/pnas.0911761106

  16. The Grants followed the fate of the immigrant over 7 generations (28 years) • The immigrant imitated (imperfectly) the local song and mated with a large female • In generation 4, severe drought, lineage reduced to a single brother and sister, which mated • From then on, this lineage was reproductively isolated—premating RIM • RIM due to song • culturally transmitted to sons (learned)? • sound may also be a consequence of bill shape

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