Population Genetics of Speciation and Demographic Inference Under Population Subdivision: Insights from Studies on Wild Tomatoes (Solanum sect. Lycopersicon)

Abstract

Multilocus sequencing studies assessing patterns of nucleotide polymorphism within and among closely related species provide valuable insights into the evolutionary processes involved in species divergence. We have employed the analytical framework of divergence population genetics in testing models of speciation in two species of wild tomatoes (clade Lycopersicon). However, all current implementations of divergence models assume panmixia within ancestral and extant species which introduces biases of potentially large magnitude, depending on the sampling scheme employed in empirical studies. Moreover, our coalescent simulations of samples from subdivided expanding populations confirm that, except at very high migration rates, sampling local populations is not equivalent to sampling from panmictic populations, with implications for studies spanning the range from Drosophila to humans. Within the constraints imposed by the complexities of the coalescent process in subdivided populations that are not accounted for in current divergence models, we found evidence for recent speciation (≤0.55 million years) of the two wild tomato species, which based on patterns of linkage disequilibrium has occurred under residual gene flow.