Comparative Phylogeography Of Ochotona Curzoniae And O. Cansus

Pikas(Lagomorpha, Ochotona) are kinds of animals which are highly adapted to alpine and arctic environments. They are sensitive to climate warming and generally treated as ideal indicators for monitoring environmental changes. O. curzoniae is mainly distributed on alpine meadows, meadow steppe and desert meadows of QinghaiTibetan Plateau(QTP) with altitude ranges from 3000 to 5000 m. O. cansus is mainly distributed on the eastern margin area of QTP. It occupies shrublands and adjacent alpine meadows. They are ideal models for studying the phylogeography of small mammals on QTP and nearby regions. By exploring their population genetic structure and demographic history, we aim to understand the unique geologic construction, landscape and climatic history of this region acted on the evolutionary history of local organisms.In the present study, we studied the population genetic structure and demographic history of Plateau pika(O. curzoniae) and Gansu pika(O. cansus) by using multiple mitochondrial loci(COI, Cytb, t RNA-Thr, t RNA-Pro, D-loop control region, totally 2417 base pairs). The results showed that there are five major lineages of O. curzoniae(Linage1-Linage5, L1-L5): samples of L1 were collected from south of Yarlung Zangbo River; L2 mainly distributed on east side of Qaidam Basin; L3 mainly obtained from southeast QTP; L4 mainly located on Amne Machin mountains; L5 principally located on southwestern QTP; XDT(Xidatan, Qinghai), WDL(Wudaoliang, Tibet), TGL(Tanggula, Tibet), three central QTP sites made into 3 lineages dispersedly. L1 was the most divergent lineage. L2 was not diverged as much as L1, but its genetic divergence was deeper than that of the other 3 lineages, which showed shallow divergence among lineages(L3, L4 and L5). The geographical barrier between L1 and the others is the Yarlung Zangbo River, while Qaidam Basin and Gonghe Basin likely acted as barriers between L2 and other lineages. Bayesian analysis of the concatenated dataset revealed two major lineages of O. cansus: Lineage 1 included samples from Baishuijiang and Tangjiahe; Lineage 2 contained samples from the other 12 locations, including all populations from eastern QTP and isolated populations from Shaanxi and Shanxi.Estimating intraspecific divergence time within two species revealed O. curzoniae had four major divergence events, at about 0.74 Ma, 0.31 Ma, 0.28 Ma, 0.19 Ma respectively. O. cansus had three: 0.72 Ma, 0.32 Ma, 0.12 Ma. The intraspecific divergence time of these two species generally coincided with the Kunhuang Movement(1.10-0.60Ma) and Gonghe Movement(0.15Ma). The two dramatic geological events during the uplift of Qinghai-Plateau, which highlighted the rise of QTP in promoting intraspecific divergence of these two species.The spacial genetic diversity pattern of O. curzoniae showed a trend of decreasing from central plateau platform to marginal regions. This is significantly different from the hypothesis that the refugia population has higher genetic diversity, while expanded population has lower genetic diversity. This is also different from the pattern of “souther diversity and northern purity” that were found in North American pikas. Interestingly, Baishuijiang showed highest population genetic diversity in O. cansus. It is located at east of Minshan Mountains. This scenario is coincident with the hypothesis that the populations from refugia have higher genetic diversity.EBSP results were different between O. curzoniae and O. cansus. O. curzoniae had experiences distinct population expansion after LGM, while O. cansus kept relatively stable throughout different historical periods. The potential distributions of these two species in four historical periods(LIG, LGM, Current, Future) were predicted by Ecological Niche Modeling. The results showed suitable habitat of O. curzoniae was smaller at LIG while larger at LGM when compared with its current distribution range. These results were in accordance with the demographic history of this species, which started to increase after LIG and had the largest population size at LGM. However, the population size of this species showed a clear trend of decreasing after LGM. Interestingly, population size of O. cansus maintained stable in different historical periods.Our results indicated that the characterization of their distribution ranges likely attribute to their different pyhlogeographic structure and demographic history. O. curzoniae occurs in homogenous platform meadow habitats. During the glacials and interglacials, the suitable habitat of this species changed dramatically, which promoted the gene flow between platform populations, and weaken the phylogeographic divergence among populations. While edge populations at lower altitude were luckily less been affected by glacial cycles, which lead to limited gene flow among populations, and then made these lineages became deeply divergent from the platform populations. However, O. cansus lives in heterogeneous alpine habitat. They can dispersal up and down during glacial cycles. It had stable population sizes and its distribution range maintained constant through different historical periods. Low level of gene flow among genetic lineages of this species likely leads to deep divergence in phylogeographic structure.We found a new pattern for the spacial distribution of populayion genetic diversity on QHP that is largely different from the hypothesis of “southern diversity, northern purity”. Based on the detailed study on distribution and historical demography of O. cansus, we may know much more about its distribution and intraspecific divergence. Dues to climate warming, the populations of both O. curzoniae and O. cansus showed clear trends of decreasing while it probably will become worse under wide range poisoning activities.