Genetic structure and phylogeography of Pyrus pashia L. (Rosaceae) in Yunnan Province, China, revealed by chloroplast DNA analyses

Abstract

In this study, we investigated two chloroplast intergenic spacers (accD-psaI and trnL-trnF) for a total of 266 individuals over 22 populations of Pyrus pashia to detect the genetic diversity, genetic, and phylogeographic structure and provide needed information for the development of conservation strategies. Thirteen haplotypes (H1–H13) were recognized. A high level of total diversity was detected (H T = 0.746). Analysis of molecular variance indicated that the genetic variation mainly existed within populations, representing 59.61 % of the total variation. Genetic differentiation among populations was high (F st = 0.404). A Mantel test did not show a correlation between the genetic and geographic distances (r = 0.139, P = 0.09, 1,000 permutations), implying that geographic distance was not critical to gene flow among populations. A significantly higher N st than G st (N st = 0.420, G st = 0.402, P < 0.05) reflected the phylogeographic structure in P. pashia. While nested clade analyses of clade 2-2 showed that restricted gene flow existed among populations, clades 1-2 and 2-1, and the total cladogram exhibited contiguous range expansion events in P. pashia. Both sum of square deviations and the raggedness index failed to reject the sudden demographic expansion model. The overall population expansion of P. pashia was estimated to occur between 621,000 and 209,000 years ago.