Genetic divergence, population differentiation and phylogeography of the cicada Subpsaltria yangi based on molecular and acoustic data: an example of the early stage of speciation?

Christopher H. Dietrich,Yunxiang Liu,Cong Wei

doi:10.1186/s12862-018-1317-8

Abstract

BackgroundGeographical isolation combined with historical climatic fluctuations have been identified as two major factors that contribute to the formation of new species. On the other hand, biotic factors such as competition and predation are also able to drive the evolution and diversification of organisms. To determine whether geographical barriers contributed to population divergence or speciation in the rare endemic cicada Subpsaltria yangi the population differentiation, genetic structure and phylogeography of the species were investigated in the Loess Plateau and adjacent areas of northwestern China by analysing mitochondrial and nuclear DNA and comparing the calling song structure of 161 male individuals.ResultsThe results reveal a low level of genetic differentiation and relatively simple phylogeographic structure for this species, but two independent clades corresponding to geographically isolated populations were recognised. Genetic and geographical distances were significantly correlated among lineages. Results of divergence-time estimation are consistent with a scenario of isolation due to glacial refugia and interglacial climate oscillation in northwestern China. Significant genetic divergence was found between the population occurring in the Helan Mountains and other populations, and recent population expansion has occurred in the Helan Mountains and/or adjacent areas. This population is also significantly different in calling song structure from other populations.ConclusionsGeographical barriers (i.e., the deserts and semi-deserts surrounding the Helan Mountains), possibly coupled with related ecological differences, may have driven population divergence and allopatric speciation. This provides a possible example of incipient speciation in Cicadidae, improves understanding of population differentiation, acoustic signal diversification and phylogeographic relationships of this rare cicada species of conservation concern, and informs future studies on population differentiation, speciation and phylogeography of other insects with a high degree of endemism in the Helan Mountains and adjacent areas.

Highlights

Geographical isolation combined with historical climatic fluctuations have been identified as two major factors that contribute to the formation of new species
Geographic isolation is essential to most speciation events, because biogeographic barriers separate populations, impede gene flow, and drive genetic differentiation, which may lead to allopatric speciation [1,2,3]
To determine whether geographical barriers are important factors driving population divergence or allopatric speciation of S. yangi, we explored the pattern of genetic divergence among populations of this species using phylogeographic analyses based on mitochondrial and nuclear gene sequences

Summary

Introduction

Geographical isolation combined with historical climatic fluctuations have been identified as two major factors that contribute to the formation of new species. Mountainous areas are thought to have harboured many refugial populations, which led to the formation of new lineages/taxa and contributed to higher genetic diversity [14, 15]. Such changes include fragmentation of previously contiguous populations which, in animals, may result in both genetic and behavioral divergence. It has been proposed that divergence in acoustic signals often plays an important part in speciation, and study of such signals has been used to discover examples of incipient or cryptic speciation [16, 17]

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Results

Discussion

Conclusion