A Complex System of Glacial Sub-Refugia Drives Endemic Freshwater Biodiversity on the Tibetan Plateau.

Catharina Clewing,Christian Albrecht,Thomas Wilke,Aristeidis Parmakelis

doi:10.1371/journal.pone.0160286

Abstract

Although only relatively few freshwater invertebrate families are reported from the Tibetan Plateau, the degree of endemism may be high. Many endemic lineages occur within permafrost areas, raising questions about the existence of isolated intra-plateau glacial refugia. Moreover, if such refugia existed, it might be instructive to learn whether they were associated with lakes or with more dynamic ecosystems such as ponds, wetlands, or springs. To study these hypotheses, we used pulmonate snails of the plateau-wide distributed genus Radix as model group and the Lake Donggi Cona drainage system, located in the north-eastern part of the plateau, as model site. First, we performed plateau-wide phylogenetic analyses using mtDNA data to assess the overall relationships of Radix populations inhabiting the Lake Donggi Cona system for revealing refugial lineages. We then conducted regional phylogeographical analyses applying a combination of mtDNA and nuclear AFLP markers to infer the local structure and demographic history of the most abundant endemic Radix clade for identifying location and type of (sub-)refugia within the drainage system. Our phylogenetic analysis showed a high diversity of Radix lineages in the Lake Donggi Cona system. Subsequent phylogeographical analyses of the most abundant endemic clade indicated a habitat-related clustering of genotypes and several Late Pleistocene spatial/demographic expansion events. The most parsimonious explanation for these patterns would be a scenario of an intra-plateau glacial refugium in the Lake Donggi Cona drainage system, which might have consisted of isolated sub-refugia. Though the underlying processes remain unknown, an initial separation of lake and watershed populations could have been triggered by lake-level fluctuations before and during the Last Glacial Maximum. This study inferred the first intra-plateau refugium for freshwater animals on the Tibetan Plateau. It thus sheds new light on the evolutionary history of its endemic taxa and provides important insights into the complex refugial history of a high-altitude ecosystem.

Highlights

Until recently, the freshwater diversity of the Tibetan Plateau and adjacent areas remained poorly understood
Specimens from the Lake Donggi Cona system build a sub-clade supported by a Bayesian posterior probabilities (BPP) of 1.0
Endemic clade 13 contained a single haplotype shared by three specimens from the Lake Donggi Cona system (BPP support for the split with the sister group is 0.96)

Summary

Introduction

The freshwater diversity of the Tibetan Plateau and adjacent areas remained poorly understood. The biogeographical patterns inferred are surprisingly complex: i) only relatively few vertebrate and invertebrate families are present on the plateau, ii) the highest biodiversity can be found in peripheral water bodies, in the major effluent river systems on the southern and eastern plateau, and iii) endemism can be high, depending on the evolutionary and life history of the species involved. Studies on Tibetan Plateau invertebrates, for example, have shown that taxa with a high passive dispersal capacity, such as amphipods of the genus Gammarus [11] and bivalves of the family Sphaeriidae [8], appear to lag pronounced endemism. At least some of these lineages appear to have diverged from their extralimital congeners prior to the Last Glacial Maximum (LGM) [6,7], 25–15 ka BP [13]

Methods

Results

Discussion

Conclusion