Dynamics behind disjunct distribution, hotspot-edge refugia, and discordant RADseq/mtDNA variability: insights from the
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RESEARCH ARTICLE
Open Access
Dynamics behind disjunct distribution, hotspot-edge refugia, and discordant RADseq/mtDNA variability: insights from the Emei mustache toad Yuchi Zheng1,2* , Qiang Dai1, Xianguang Guo1 and Xiaomao Zeng1
Abstract Background: The distribution of genetic diversity and the underlying processes are important for conservation planning but are unknown for most species and have not been well studied in many regions. In East Asia, the Sichuan Basin and surrounding mountains constitute an understudied region that exhibits a “ring” of high species richness overlapping the eastern edge of the global biodiversity hotspot Mountains of Southwest China. We examine the distributional history and genetic diversification of the Emei mustache toad Leptobrachium boringii, a typical “ring” element characterized by disjunct ranges in the mountains, by integrating time-calibrated gene tree, genetic variability, individual-level clustering, inference of population splitting and mixing from allele frequencies, and paleoclimatic suitability modeling. Results: The results reveal extensive range dynamics, including secondary contact after long-term isolation via westward dispersal accompanied by variability loss. They allow the proposal of a model that combines recurrent contractions caused by Quaternary climatic changes and some failed expansions under suitable conditions for explaining the shared disjunct distribution pattern. Providing exceptional low-elevation habitats in the hotspot area, the eastern edge harbors both long-term refugial and young immigrant populations. This finding and a synthesis of evidence from other taxa demonstrate that a certain contributor to biodiversity, one that preserves and receives low-elevation elements of the east in this case, can be significant for only a particular part of a hotspot. By clarifying the low variability of these refugial populations, we show that discordant mitochondrial estimates of diversity can be obtained for populations that experienced admixture, which would have unlikely left proportional immigrant alleles for each locus. (Continued on next page)
* Correspondence: [email protected] 1 Chengdu Institute of Biology, Chinese Academy of Sciences, #9 of Section 4, Ren-Min-Nan Road, Wuhou District, Chengdu 610041, Sichuan Province, China 2 Key Laboratory of Southwest China Wildlife Resources Conservation (Ministry of Education), China West Normal University, Nanchong 637009, Sichuan Province, China © The Author(s). 2020 Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is
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