Ongoing Speciation in the Tibetan Plateau Gymnocypris Species Complex

Renyi Zhang,Xiaoni Gan,Guogang Li,Cunfang Zhang,Yongtao Tang,Shunping He,Kai Zhao,Zuogang Peng,Thomas Mailund

doi:10.1371/journal.pone.0071331

Abstract

Local adaptation towards divergent ecological conditions often results in genetic differentiation and adaptive phenotypic divergence. To illuminate the ecological distinctiveness of the schizothoracine fish, we studied a Gymnocypris species complex consisting of three morphs distributed across four bodies of water (the Yellow River, Lake Qinghai, the Ganzi River and Lake Keluke) in the Northeast Tibetan Plateau. We used a combination of mitochondrial (16S rRNA and Cyt b) and nuclear (RAG-2) genetic sequences to investigate the phylogeography of these morphs based on a sample of 277 specimens. Analysis of gill rakers allowed for mapping of phenotypic trajectories along the phylogeny. The phylogenetic and morphological analyses showed that the three sparsely rakered morphs were present at two extremes of the phylogenetic tree: the Yellow River morphs were located at the basal phylogenetic split, and the Lake Keluke and Ganzi River morphs at the peak, with the densely rakered Lake Qinghai morphs located between these two extremes. Age estimation further indicated that the sparsely rakered morphs constituted the oldest and youngest lineages, whereas the densely rakered morph was assigned to an intermediate-age lineage. These results are most compatible with the process of evolutionary convergence or reversal. Disruptive natural selection due to divergent habitats and dietary preferences is likely the driving force behind the formation of new morphs, and the similarities between their phenotypes may be attributable to the similarities between their forms of niche tracking associated with food acquisition. This study provides the first genetic evidence for the occurrence of convergence or reversal in the schizothoracine fish of the Tibetan Plateau at small temporal scales.

Highlights

The discovery of the ecological and evolutionary forces responsible for population divergence and adaptation has long been a major objective of evolutionary biology [1,2,3,4]
43, 22 and 34 unique haplotypes were defined for the Cyt b, 16S rRNA and RAG-2 genes, respectively; we combined the sequences from the three DNA regions to assess variation
The ‘‘Gonghe Movement’’ event of the Tibetan Plateau in the Late Pleistocene led to the uplift of the present barrier, and the single body of water was separated into its current configuration of two large water systems (Fig. 1) [36,60,61,62]

Summary

Introduction

The discovery of the ecological and evolutionary forces responsible for population divergence and adaptation has long been a major objective of evolutionary biology [1,2,3,4]. Local adaptation driven by differing ecological conditions often results in the adaptive phenotypic and genetic divergence of geographically isolated populations [1,5,6,7] and may drive the formation of new taxa [7,8,9,10] Such a process requires a source of divergent selection, for which environmental differences and niche adaptation are driving mechanisms [1,3,11,12]. Schizothoracine fish are specialized for high-elevation rivers and exhibit a number of unique adaptations to the Tibetan Plateau [24,25]. This large taxon has become an important model for research on speciation in nature and the ecological factors underlying divergence in general [26,27,28,29]. We demonstrate an evidence of ongoing speciation with a tendency to retain the ancestral phenotype on the complex by convergence or reversal

Methods

Results

Conclusion