Abstract
Population genetic structure, historical biogeography and historical demography of the alpine toad Scutiger ningshanensis were studied using the combined data mtDNA cytochrome b (cyt b) and the mtDNA cytochrome c oxidase subunit I (COI) as the molecular markers. This species has high genetic variation. There was a significant genetic differentiation among most populations. Three lineages were detected. The phylogenetic relationship analyses and the SAMOVA (spatial analysis of molecular variance) results showed significant phylogeographic structure. 82.15% genetic variation occurred among populations whereas differentiation within populations only contributed 17.85% to the total. Mantel test results showed a significant correlation between the pairwise calculated genetic distance and pairwise calculated geographical distance of the populations (regression coefficient = 0.001286, correlation coefficient = 0.77051, p (rrand≥robs) = 0.0185<0.05), indicating the existence of isolation-by-distance pattern of genetic divergence for cyt b + COI sequence, which suggests that the distribution of genetic variation is due to geographical separation rather than natural selection. The population expansion or contraction and genetic differentiation between populations or lineages could be explained by topography and the repetitive uplifts of the Tsinling Mountains and the climatic cycles during the late Pliocene and Pleistocene. S. ningshanensis experienced a rapid population expansion about 40,000 years before present. The current decline in population size was probably caused by anthropogenic disturbance. Current populations of S. ningshanensis are from different refugia though the location of these refugia could not be determined in our study. Topography, climatic changes and repetitive population expansion/contraction together led to the high level of genetic variation in S. ningshanensis. A total of three management units (MUs) was determined, which must be considered when conservation policy is made in the future.
Highlights
Population genetic structure refers to the geographical pattern of genetic diversity within or among populations
Other than the reports on collection of additional specimens, only the biological characteristics of tadpoles of this species was studied [33]. The habitat of this species was roughly divided into two parts: the western part and the eastern part. Is this geographical pattern caused by habitat fragmentation or by populations from different glacial refugia? Does the isolation by distance between the local populations result in occurrence of any speciation events? The aims of the present study were to explore the population genetic structure, historical biogeography and the historical demography of S. ningshanensis
To make an extensive sampling, we explored the whole Tsinling Mountains, and collected this species at two locations where the distribution of this species has not been recorded
Summary
Population genetic structure refers to the geographical pattern of genetic diversity within or among populations. It could be influenced by gene flow, genetic drift, selection, mutation and recombination. Estimation of the gene flow level allows conservation biologists to understand the relationships between populations and assess levels of genetic variation in order to evaluate the relative levels of conservation concern hierarchically across populations in a species. Genetic drift is the change in the frequency of a gene variant in a population due to random sampling [2]. Http://en.wikipedia.org/ wiki/Genetic_drift - cite_note-Masel_2011-1#cite_note-Masel_2011-1Genetic drift may lead to disappearance of gene variants and thereby reduce genetic diversity. Phylogeography connects historical processes in evolution with spatial distributions [4]. The statistical phylogeography is one of the widely used approaches in phylogeography, which takes into account the stochasticity of genetic processes into demographic inference based on coalescent models for parameter estimation [4,5]
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