The effect of long-term historical habitat fragmentation on genetic diversity of the relictual conifer Calocedrus macrolepis (Cupressaceae) in China

Abstract

Geological events and glacial history have all induced habitat fragmentation, which has long been recognized as a major threat to the survival of many species. However, fragmentation has differential effects on population genetic patterns of individual species, such as loss of genetic diversity, genetic differentiation enhance, inbreeding increase, allelic deletion, and no effect. Calocedrus macrolepis Kurz is an endangered ancient relictual and fragmented conifer. In this study, the genetic diversity and structure were analyzed to shed light on the factors that determine their contemporary genetic patterns and to provide optimum strategies for future conservation. The genetic diversity within and among 14 extant populations of C. macrolepis was analyzed using nine microsatellite markers. The genetic diversity (H E = 0.636), genetic differentiation (F ST = 0.163), and gene flow (Nm = 1.496) were disclosed, respectively. No significant correlation was detected by the Mantel test between genetic and geographical distances among pair-wise comparisons of populations (r = 0.197, P = 0.103). Fourteen populations could be generally assigned to two separate groups, and significant asymmetrical migration among populations within the regional groups was revealed. Both Quaternary glaciations and neotectonic movements seem to be associated with a long history of population contraction and fragmentation of C. macrolepis, enhancing its genetic drift and population divergence. The results indicate that long-term habitat fragmentation could be responsible for the genetic structure observed. In situ conservation strategies should be designed, especially small and isolated populations. Also, special attention should be given to populations LY and DZ because of their private alleles, as well as to population CJ isolated from the mainland.