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 Drift may facilitate speciation, but probably cannot often cause speciation on its own
Ecological Speciation Sister species in the same lake Big is benthic, small is limnetic No interbreeding in nature– habitat isolation or pre- mating RIM?
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 No-choice mating trials in the lab
RIM appears to be body size—did divergent natural selection on body size speciation?
Speciation via Sexual Selection Many sister lineages with same ecological niche, but different secondary sexual characters
Greater species diversity in lineages with greater promiscuity. Due to stronger sexual selection?
Fig EXPERIMENT Normal light Monochromatic orange light P. pundamilia P. nyererei Speciation by Sexual Selection Under manipulated lighting, females made “wrong” mate choice
Genetics and Timing of Speciation
Time to Speciation Varies
Fig One-gene speciation
RIM’s can be generated by simple differences in genetics
Ancestral species: Triticum monococcum (2n = 14) AABB Wild Triticum (2n = 14) Product: AA BB DD T. aestivum (bread wheat) (2n = 42) Wild T. tauschii (2n = 14) DD Speciation may involve hybridization, so it can be quick for many species
Speciation involves a stochastic element… Medium ground finches on Daphne major (Gallapagos Island)
Top to bottom: A to F show successive generations of the hybrids, which now mate only with each other. Grant and Grant, PNAS, doi/ /pnas Immigrant F1 F5 F6 Immigrant Geospiza fortis: large body, wide beak, unusual song (bad mimicry)
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