Speciation in Caucasian lizards: climatic dissimilarity of the habitats is more important than isolation time

Abstract

Given sufficient time and limited gene flow, evolutionary lineages tend to transform into separate species. Mechanisms preventing assimilation during repeated gene‐flow events include divergent adaptations and the development of pre‐ or postzygotic isolation. We analysed the morphological and genetic boundaries of three species of the rock lizard clade Darevskia ‘rudis’ (Darevskia rudis, Darevskia valentini, and Darevskia portschinskii) in relation to the environment, and tried to reconstruct evolutionary pathways underlying the observed separation among the species. We studied the geographic distribution of the scalation traits, microsatellite genotypes, and mitochondrial haplotypes. Our analyses showed consistent morphological and genetic patterns at the centre of the ranges for each species, but asymmetric distribution of alleles and scalation characters within the current contact zones among the species. The genetic and morphological diversification of the clade has been shaped during glacial isolation in an area of Southern Caucasus, away from the Black Sea Coast. The ancestral lineage of D. portschinskii separated from the common D. rudis–D. valentini lineage in the middle Pleistocene, and the two latter lineages separated in relatively recent geological time. Neither of the lineages attained complete lineage sorting; moreover, isolation and migration modelling have helped to detect recombinant gene flow from D. rudis to D. portschinskii (but not to D. valentini). This is most likely linked with climatically more similar suitable habitats between D. rudis and D. portschinskii than between D. valentini and the other two species. In itself, the isolation period was insufficient for the development of intrinsic isolation mechanisms in the system studied. Thus, differential landscape‐dependent selection within the contact zones is likely to have triggered the rapid development of isolation mechanisms. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2013, 109, 876–892.

Geographical patterns of species richness and beta diversity of Larentiinae moths (Lepidoptera: Geometridae) in two temperate biodiversity hotspots

“…High values of spatial turnover, especially across latitude, for both regions indicate nonoverlapping small range distributions for most species and the importance of speciation in both hotspots. This prediction is consistent with molecular evidence and ecological modelling from moth species and other taxa (Rajaei Sh et al 2013;Tarkhnishvili et al 2013). These studies suggest that divergence and speciation of the lineages happened during the Pleistocene glacial and postglacial cycles, as a serious bottleneck for lineage sorting and a promoter for habitat fragmentation and adaptation of surviving populations to the climate conditions of differential refugia.…”

“…Both the Caucasus and the Irano-Anatolian BHs have been documented as principal refugial areas for present-day fauna and flora of the west Palearctic. Molecular evidence suggests existence of potential species-specific refugial areas and consequently a narrow distribution for many species (Ahmadzadeh et al 2013;Rajaei Sh et al 2013;Seddon et al 2002;Tarkhnishvili et al 2013).…”

Phylogeography and morphological variation in a narrowly distributed Caucasian rock lizard, Darevskia mixta

“…During 2009-2014 our team members studied several hundred rock lizard locations in Georgia and NE Turkey (Tarkhnishvili et al, 2010;Tarkhnishvili, 2012;Tarkhnishvili, Murtskhvaladze and Gavashelishvili, 2013;Tarkhnishvili et al, unpublished). All previously recorded locations for D. mixta (Darevsky, 1967;Murphy et al, 2000;Tarkhnishvili et al, 2010) were included, and augmented with additional populations.…”

“…Partial DNA sequence from the mitochondrial locus cytochrome b (cytb) was used in the analysis -cytb has been shown to be sufficiently variable among closely related species of Darevskia to allow resolution of species relationships (Fu, Murphy and Darevsky, 1997;Murphy et al, 2000;Tarkhnishvili, Murtskhvaladze and Gavashelishvili, 2013). A cytb fragment (714 bp) was amplified using primer pairs H15915-L15369 and H15488-L15153 (Fu, 2000;Murphy et al, 2000).…”

Comparing developmental stability in unisexual and bisexual rock lizards of the genusDarevskia

“…Recent findings even suggest that in some cases more than two parental species may have been involved (Tarkhnishvili, Murtskhvaladze, & Anderson, 2017). There is evidence that genetic introgression and backcrossing took place among various species of Darevskia lizards, so one should keep in mind that the genetic background of unisexual hybrids might be more complex (Darevsky, 1967;Freitas et al, 2016;Tarkhnishvili, Murtskhvaladze, & Gavashelishvili, 2013). All parthenogenetic Darevskia are diploid (2n = 38), which makes the overall assessment of their characters clearer as there are no triploid lineages, known to occur in other unisexual taxa (Danielyan et al, 2008;Darevsky, 1966;Schön, Van Dijk, & Martens, 2009).…”