Long-term sky islands generate highly divergent lineages of a narrowly distributed stream salamander (Pachyhynobius shangchengensis) in mid-latitude mountains of East Asia

Abstract Background Climate oscillation may have a profound effect on species distributions, gene flow patterns and population demography. In response to environmental change, those species restricted to montane habitats experienced expansions and contractions along elevation gradients, which can drive differentiation among sky islands. Results The Shangcheng stout salamander (Pachyhynobius shangchengensis) is a cool stream amphibian restricted to high-elevation areas in the Dabie Mountains, East China. In the present study, we used mtDNA genes (Cyt b and ND2) of 193 individuals and 12 nuclear microsatellite loci genotyped on 370 individuals, representing 6 populations (JTX, KHJ, MW, TTZ, BYM and KJY) across the taxon’s distribution area, to investigate their genetic variation and evolutionary history of P. shangchengensis. Most populations showed unusually high levels of genetic diversity. Phylogenetic analyses revealed five monophyletic clades with divergence times ranging from 3.96 to 1.4 Mya. Accordingly, significant genetic differentiation was present between these populations. Bayesian skyline plot analyses provided that all populations underwent long-term population expansions since the last inter-glacial (0.13 Mya ~ 0.12 Mya). Msvar analyses found recent signals of population decline for two northern populations (JTX and KHJ) reflecting a strong bottleneck (approximately 15-fold decrease) during the mid-Holocene (about 6000 years ago). Ecological niche modelling has shown a discontinuity in suitable habitats for P. shangchengensis under different historical climatic conditions. Conclusions Our results suggest that the niche conservatism of P. shangchengensis and sky island effects may have led to long-term isolation between populations. In sky island refuges, the mid-latitude Dabie Mountains have provided a long-term stable environment for P. shangchengensis, which has led to the accumulation of genetic diversity and has promoted genetic divergence