Chloroplast phylogeography of the East Asian Arcto‐Tertiary relict Tetracentron sinense (Trochodendraceae)

Abstract

Aim A phylogeographical study of the widespread but phylogenetically isolated East Asian endemic tree species Tetracentron sinense (Trochodendraceae) was performed to evaluate whether and how Pleistocene and pre‐Pleistocene climate changes helped to influence current phylogeographical patterns, and to describe the current patterns of genetic diversity and their implications for conservation. Location Southwestern and central subtropical China. Methods Sequences of four chloroplast spacer regions were obtained from 157 individuals of T. sinense . A haplotype network was constructed using tcs . Genetic diversity and differentiation, spatial analysis of molecular variance ( SAMOVA ) and analysis of molecular variance ( AMOVA ) were used to test for genetic structure. beast was used to estimate the divergence times between haplotypes. Historical demographic expansion was tested using pairwise mismatch distribution analysis. Results Of the 21 recovered haplotypes, three were widely distributed, but most were restricted to particular regions. Populations with high haplotype diversity were located in western Hubei, southern Sichuan and southern Chongqing. The two earliest‐diverging haplotypes were found in southwestern China. The haplotype distribution of T. sinense demonstrated significant phylogeographical structure ( N ST > G ST ; P 0.05). The best partitioning of genetic diversity by SAMOVA ( K = 5) produced groups that matched the main tcs ‐derived clades. Two independent range expansions within SAMOVA ‐derived groups 2 and 3 were dated to approximately 399 and 311 ka, respectively. The time to the most recent common ancestor of all haplotypes was 9.6 (95% highest posterior density: 27.0–2.2) Ma, but most of the haplotype diversity appeared during the Quaternary. Main conclusions The extant distribution of T. sinense is likely to have been shaped by both pre‐Quaternary and Pleistocene climate changes. Southwestern China may have served as an important refugium for T. sinense throughout the Neogene, while the species also occupied multiple refugia during the late Pleistocene glacial periods. Populations of T. sinense were resolved into five allopatric groups, between which there is apparently no seed movement.

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