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Keywords:

  • Elevation shifts;
  • montane species;
  • Pleistocene climatic oscillations;
  • statistical phylogeography;
  • West Lesser Caucasus hotspot

Abstract

Localized up-down altitudinal shifts and subsequent isolation–admixture of montane species in response to glacial cycles has been proposed as a mechanism for the high diversity along Anatolian mountains. However, specific predictions of the proposed mechanism (the elevation shift model) have yet to be tested. Here, we provide a first assessment of this model for promoting inter- and intraspecific genetic diversity in the bush-cricket genus Phonochorion endemic to the West Lesser Caucasus hotspot. Mitochondrial genes were analysed by Bayesian Markov Chain Monte Carlo inferences and coalescent simulations. Timing of diversification was estimated using a multispecies coalescent model. Divergence with gene flow was tested using an isolation with migration model. Population genetic parameters and genetic structuring were determined using Bayesian coalescent methods and spatial analysis. Demographic history was assessed using mismatch distributions and extended Bayesian skyline plots. Speciation events corresponded both to the Miocene and Pleistocene while intraspecific divergence was Pleistocene based. There was evidence for moderate levels of gene flow between species during diversification; however, incomplete lineage sorting could explain the data as well as gene flow. Overall diversification patterns within the genus Phonochorion agree with the predictions of the elevations shift model. Genetic patterns of diversification were driven mainly by Pleistocene glacial cycles and reflected the nature and distribution of sky islands. There was also some albeit weak evidence of demographic expansions coinciding with glacial cooling. However, evidence for divergence with gene flow was inconclusive.