Fine- and landscape-scale spatial genetic structure of cushion rockjasmine, Androsace tapete (Primulaceae), across southern Qinghai-Tibetan Plateau.

The cushion rockjasmine, Androsace tapete (Primulaceae), is among the angiosperms with highest altitudal distribution in the world. Cushion rockjasmine is a prominent pioneer species in alpine deserts and alpine flowstone slope habitats up to 5,300 m on Qinghai-Tibetan Plateau. In this study, we use inter simple sequence repeat (ISSR) markers to investigate the spatial genetic structure of A. tapete at both fine-scale and landscape-scale, with emphasis on testing the hypothesis that the low-altitude valley of the Brahmaputra River, running from west to east across Qinghai-Tibetan Plateau, has significant effects on the spatial population structure of A. tapete. A total of 235 individuals were collected from five populations in disjunct ridges (i.e. two populations located in the north, and three in the south of the Brahmaputra River), including 158 individuals that were spatial explicitly sampled from a 30 m x 90 m plot. At fine scale, spatial autocorrelation analysis indicates a significant genetic structure within a short distance (less than 10 m), which is probably due to limited gene dispersal via pollen and/or seeds. At landscape scale, however, AMOVA suggests that most of the total genetic variation (85%) is among individuals within populations; and the Brahmaputra River plays a weak role in shaping the spatial population structure of A. tapete. In addition, the results of PCA and STRUCTURE assignment show significant genetic associations between the populations across the Brahmaputra River. The historical gene exchanges and slow genetic drift may be responsible for the lack of deep genetic differentiation among topographically separated populations in A. tapete.