Understudied regions and messy taxonomy: Geography, not taxonomy, is the best predictor for genetic divergence of the Poecilimon bosphoricus species group

Abstract

The complex and dynamic history of the Anatolian Peninsula during the Pleistocene set the stage for species diversification. However, the evolutionary history of biodiversity in the region is shrouded by the challenges of studying species divergence in the recent, dynamic past. Here, we study the Poecilimon bosphoricus (PB) species group to understand how the bush crickets' diversification and the regions' complex history are coupled. Specifically, using sequences of two mitochondrial and two nuclear gene segments from over 500 individuals for a comprehensive set of taxa with extensive geographic sampling, we infer the phylogenetic and geographic setting of species divergence. In addition, we use the molecular data to examine hypothesized species boundaries that were defined morphologically. Our analyses of the timing of divergence confirm the recent origin of the PB complex, indicating its diversification coincided with the dynamic geology and climate of the Pleistocene. Moreover, the geography of divergence suggests a history of fragmentation followed by admixture of populations, suggestive of a ring species. However, the evolutionary history based on genetic divergence conflicts with morphologically defined species boundaries raising the prospects that incipient species divergences may be relatively ephemeral. As such, the morphological differences observed in the PB complex may not to be sufficient to have prevented homogenizing gene flow in the past. Alternatively, with the recent origin of the complex, the lack of time for lineage sorting may underlie the discord between morphological species boundaries and genetic differentiation. Under either hypothesis, geography—not taxonomy—is the best predictor of genetic divergence.