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Molecular evidence for fragmentation among populations of Taxus wallichiana var. mairei, a highly endangered conifer in China

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Taxus wallichiana var. mairei (Lemée & Léveillé) L. K. Fu & Nan Li is a highly endangered conifer in China. It is dioecious and wind pollinated, with seed dispersal by animals. Extant natural populations on mainland China and Taiwan are highly scattered, largely as a result of habitat loss and overexploitation. Intersimple sequence repeat (ISSR) markers were employed to assess the genetic structure among 464 individuals from 17 populations across the variety’s distribution range in the Sino–Japanese and Malesian floristic subkingdoms. ISSRs revealed a high genetic diversity (percentage of polymorphic loci = 98.4%, Nei’s gene diversity = 0.3467, Shannon’s information index = 0.5152) at the species level and high differentiation among populations (coefficient of gene differentiation = 0.4066; B = 0.4376). Gene flow among populations was found to be limited to the mainland populations. A UPGMA (unweighted pair group method with arithmetic mean) dendrogram suggests that the population in Taiwan is genetically the most isolated, while among the mainland populations a trend of an east–west split is suggested. This finding is supported by the analysis of molecular variance. The pattern of genetic variation suggests that the extant distribution of T. wallichiana var. mairei is the result of the fragmentation of a historically more continuous distribution. Conservation measures for this highly endangered plant are discussed, and an integrated approach to increase plant density and connectivity among the remaining populations is suggested.

Taxus wallichiana var. mairei (Lemée & Léveillé) L. K. Fu & Nan Li est un conifère chinois très menacé. C’est une espèce dioïque et anémophile dont les graines sont dispersées par les animaux. Les populations naturelles qui subsistent en Chine continentale et à Taiwan sont très fragmentées en raison de la surexploitation et de la perte d’habitats. Les auteurs ont utilisé des marqueurs des régions intermicrosatellitaires (ISSR) pour évaluer la structure génétique de 464 individus dans 17 populations représentatives de la répartition naturelle de l’espèce dans les sous-régions floristiques malaisienne et sino-japonaise. Les marqueurs ISSR ont révélé une grande diversité génétique au niveau de l’espèce (PPB = 98,4 %, HE = 0,3467, I = 0,5152) et une forte différenciation parmi les populations (GST = 0,4066; B = 0,4376). Le flux génique parmi les populations était limité aux populations continentales. Un dendrogramme UPGMA indique que la population de Taiwan est génétiquement la plus isolée et que les populations continentales ont tendance à se dissocier selon un axe est-ouest, ce qui est supporté par AMOVA. Ce patron de variation génétique indique que la distribution actuelle de T.wallichiana var. mairei est le résultat de la fragmentation d’une distribution historiquement plus continue. Les auteurs discutent de mesures de conservation pour cette espèce fortement menacée; ils suggèrent d’adopter une approche intégrée pour augmenter la densité des populations résiduelles ainsi que leur connectivité.

Document Type: Research Article

Publication date: April 1, 2009

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