Low genetic diversity and high inbreeding of the endangered yews in Central Himalaya: implications for conservation of their highly fragmented populations

AimTo assess patterns of genetic variation and levels of diversity in the endangered allopatrically distributed Taxus contorta, T.mairei and T.wallichiana in highly fragmented and degraded habitats of the Himalayas. LocationCentral Himalaya, particularly the area within the political boundary of Nepal and SW Xizang, China. MethodsWe used a multidisciplinary approach combining a transect study, population genetic analyses based on chloroplast DNA sequences and nuclear microsatellite data, and ecological modelling to estimate the size-class structure, genetic diversity and differentiation of populations and understand the potential fate of yew populations in the face of rapidly degrading habitats and abrupt climate change. ResultsFor all three species, the flat regression slopes of the size-class distributions (SCD), and high permutation index values indicate unstable population structure with lower recruitment rates. The chloroplast and nuclear microsatellite data further reveal low genetic diversity, significant population differentiation and high inbreeding for yew species of this region. We identified two strong barriers of genetic discontinuities, where the presence of spatially different ecological environments caused an allopatric distribution of the species. The ecological model projection for the year 2080 forecasted a substantial decrease in size of suitable areas and a range shift towards the north. Main conclusionsThe spatial distribution of the genetic variation and diversity within and among the populations of each yew species was largely shaped by their peripheral position in their respective ranges, differences in their evolutionary histories, and the periodic and asynchronous climates experienced by the species, in addition to the severe impacts of anthropogenic activities. Several yew populations in Central Himalaya have already declined to sizes too small to be demographically sustainable. Improved conservation managements, both at the species and landscape levels, should be implemented for the protection of remnant populations.