Budding speciation via peripheral isolation: the Psorodonotus venosus (Orthoptera,Tettigoniidae) species group example

The peripatric or budding species model has remained theoretical until recently. The habitat preference and range pattern of the mountainous Psorodonotus venosus species group, distributed in Anatolia and Caucasus, offered potential to test the predictions of the model. The study aimed to confirm the parameters and to provide evidence for peripatric speciation in a terrestrial group. Fourteen populations representing the total range of the group were studied. Sequences of two mitochondrial fragments including four loci (12S rDNA+tDNAval+16S rDNA and COI) and a nuclear fragment including three loci (ITS1+5.8S rDNA+ITS2) were obtained and used in phylogenetic, time estimation, population genetics and demographic analyses. Additionally, phenotypical data were provided for the group. Phylogenetic analyses supported the monophyly of the PVG and suggested similar intralineage relationships, but did not support the monophyly of each of the species in the group. The molecular chronograms indicated radiation of the group throughout the Pleistocene. Demographic analyses suggested constant population sizes for the populations in the centre of the range but a significant departure from constancy in four peripheral populations. Genetic diversity is significantly reduced in peripheral populations, but not in others. We arrived to following conclusions. The data suggest that P. venosus is the ancestral species and P. rugulosus, P. tendurek and P. hakkari are bud species, as their haplotypes are nested within P. venosus. As expected under the budding speciation model, (i) in contrast to ancestral species, genetic diversity is reduced, and there are signs of departure from constant population size in bud species; (ii) bud species have isolated and restricted ranges, while the ancestral species does not, (iii) the relative ages of ancestral and bud species are the most reliable data to confirm the model, and chronograms of PVG well support this prediction, and (iv) the divergence events in the group co‐occurred with major climatic transformations of the Pleistocene.