Spiroides shrubs on Qinghai-Tibetan Plateau: Multilocus phylogeography and palaeodistributional reconstruction of Spiraea alpina and S. Mongolica (Rosaceae)

A common hypothesis for the rich biodiversity found in mountains is uplift-driven diversification. Using a multilocus approach, here we assessed the influence of Qinghai-Tibetan Plateau (QTP) uplift and fluctuating regional climate on genetic diversity of two sister spiroides shrubs, Spiraea alpina and S. mongolica. Combined with palaeodistributional reconstruction modelling, we investigated the current and past-predicted distribution of these species under different climatic episodes. The study demonstrated that continuous pulses of retreat and expansion during last glacial-interglacial episodes, combined with the uplifting of QTP shaped the current distribution of these species. All the populations showed high level of genetic diversity based on both cpDNA and SSR markers. The average gene diversity within populations based on cpDNA markers was 0.383 +/- 0.052 for S. alpina and 0.477 +/- 0.048 for S. mongolica. The observed and expected heterozygosities based on SSR for both Spiraea alpina and S. mongolicawere H-E(0.72-0.90)/H-O(0.35-0.78) and H-E(0.77-0.92)/H-O(0.47-0.77) respectively. Palaeodistributional reconstruction indicated species' preferences at southeastern edge of the plateau during last glacial maximum, at higher altitude areas of QTP and range expansion to central plateau during the interglacial episodes. Assignment tests in STRUCTURE, discriminant analysis of principal coordinates and Immigrants analysis in GENECLASS based on nuclear SSR markers did not support the hypothesis of gene flow between both the species. However, maximum likelihood approach based on cpDNA showed sharing of haplotypes between both species.