Genetic differentiation of relictual populations of Alsophila spinulosa in southern China inferred from cpDNA trnL–F noncoding sequences

Abstract

The genetic differentiation and phylogeographical pattern of 11 relictual populations of Alsophila spinulosa distributed across Hainan, Guangdong, and Guangxi in southern China were inferred from sequence variations of trnL–F noncoding regions of chloroplast DNA (cpDNA). The length of trnL–F noncoding sequences varied from 863 to 940 bp. The A + T content was 62.23–63.36%. Sequences were neutral in terms of evolution (Tajima’s criterion D = −0.62417, P > 0.10 and Fu and Li’s test D* = −1.45455, P > 0.10; F* = −1.32798, P > 0.10). Thirty-four haplotypes were identified based on nucleotide variation. Relatively high levels of haplotype diversity ( h = 0.929) and nucleotide diversity ( Dij = 0.022263) were detected in A. spinulosa, probably associated with its long evolutionary history which allowed the accumulation of genetic variation within lineages. Both the minimum spanning network and the strict consensus tree of the most parsimonious trees generated for haplotypes demonstrated that the investigated populations of A. spinulosa were subdivided into two geographical groups: Hainan and Guangdong–Guangxi. An analysis of molecular variance (AMOVA) indicated that most of the genetic variation (87.48%, P < 0.001) was partitioned among regions. Spatial structure measurements revealed that population genetic structure was not related to geographical distance. This research suggests that blocked gene flow by Qiongzhou strait and an inbreeding system might result in the geographical subdivision between Hainan and Guangdong–Guangxi ( F ST = 0.92, Nm = 0.09). Within each region, the “star like” pattern of phylogeography of haplotypes implied a population expansion process during evolutionary history. Gene genealogies together with coalescent theory were useful tools for uncovering the phylogeography of A. spinulosa.