Population genetics of speciation in two closely related wild tomatoes (Solanum section lycopersicon)

We present a multilocus sequencing study to assess patterns of polymorphism and divergence in the closely related wild tomato species, Solanum peruvianum and S.chilense (Solanum section Lycopersion, Solanaceae). The data set comprises seven mapped nuclear loci (approximate to 9.3 kb of analysed sequence across loci) and four local population samples per species that cover much of the species ' range (between 80 and 88 sequenced alleles across both species). We employ the analytical framework of divergence population genetics (DPG) in evaluating the utility of the isolation model of speciation to explain observed patterns of polymorphism and divergence. Whereas the isolation model is not rejected by goodness-of-fit criteria established via coalescent simulations, patterns of intragenic linkage disequilibrium provide evidence for postdivergence gene flow at two of the seven loci. These results suggest that speciation ocurred under residual gene flow, implying that natural selection is one of the evolutionary forces driving the divergence of these tomato species. This interference is fully consistent with their divergence, conservatively estimated to be <= 0.55 million years. We discuss possible biases in the demographic parameter estimates due to the current restriction of DPG algorithms to panmictic species.