Barej Michael F, Penner Johannes, Schmitz Andreas, Rödel Mark-Oliver
Museum für Naturkunde Berlin, Leibniz Institute for Evolution and Biodiversity Science, Invalidenstrasse 43, D-10115, Berlin, Germany.
Department of Herpetology and Ichthyology, Natural History Museum of Geneva, CP 6434, 1211, Geneva 6, Switzerland.
BMC Evol Biol. 2015 Apr 19;15:67. doi: 10.1186/s12862-015-0346-9.
Correct species identification is crucial in different fields of biology, and in conservation. The endemic West African frog family Odontobatrachidae currently contains a single described species, Odontobatrachus natator. From western Guinea to western Côte d'Ivoire it inhabits forests around waterfalls or cascades. Based on more than 130 specimens from 78 localities, covering the entire distribution, we investigated the molecular diversity of these frogs.
Our analyses included mitochondrial and nuclear genes, with a concatenated alignment of 3527 base pairs. We detected high level of genetic differentiation with five distinct lineages or operational taxonomic units (OTUs). These OTUs were also identified by two different species delimitation approaches, Generalized Mixed Yule Coalescent (GMYC) and cluster algorithm. All OTUs occur in parapatry in the Upper Guinean forests. One OTU, assigned to the "true" Odontobatrachus natator, covers the largest distribution, ranging from the border region of western Sierra Leone-Guinea to eastern Liberia. Two OTUs are restricted to western Guinea (Fouta Djallon and foothills), while two others occur in eastern Guinea and the border region of Guinea-Liberia-Côte d'Ivoire. The OTU representing O. natator consists of two divergent subclades: one restricted to the Freetown Peninsula (Sierra Leone) and the other covering all populations further inland. Environmental niche models indicated that the restricted Freetown Peninsula population is separated by unsuitable habitat from remaining populations.
Geographic isolation of OTUs and molecular differences comparable to species level differentiation in other frog families indicate that O. natator contains cryptic species diversity. Respective distribution patterns most probably resulted from repeated changes of forest cover (contraction and expansion) over evolutionary timescales. The survival within forest refugia that have persisted through multiple drier periods and subsequent dispersal during wetter times may best explain the observed geographic distributions of OTUs. According to the IUCN Red List range criteria each OTU should be classified as "Endangered." If the Freetown Peninsula "natator" population is recognized as a distinct species it would warrant recognition as "Critically Endangered." The identification of cryptic lineages highlights the urgent need to protect these frogs, all of which are endemic to small areas within the Upper Guinean biodiversity hotspot.
正确的物种鉴定在生物学的不同领域以及保护工作中都至关重要。西非特有的齿蟾科目前仅包含一个已描述的物种，即游泳齿蟾。它分布于从几内亚西部到科特迪瓦西部，栖息在瀑布或小瀑布周围的森林中。基于来自78个地点的130多个标本，涵盖其整个分布范围，我们对这些青蛙的分子多样性进行了研究。
我们的分析包括线粒体和核基因，串联比对长度为3527个碱基对。我们检测到高度的遗传分化，存在五个不同的谱系或操作分类单元（OTU）。这些OTU也通过两种不同的物种界定方法，即广义混合尤尔合并法（GMYC）和聚类算法得以识别。所有OTU在几内亚上几内亚森林中呈邻域分布。一个OTU，被认定为“真正的”游泳齿蟾，分布范围最大，从塞拉利昂 - 几内亚边境地区到利比里亚东部。两个OTU局限于几内亚西部（富塔贾隆高原及山麓），另外两个分布在几内亚东部以及几内亚 - 利比里亚 - 科特迪瓦边境地区。代表游泳齿蟾的OTU由两个不同的亚分支组成：一个局限于弗里敦半岛（塞拉利昂），另一个涵盖所有内陆地区的种群。环境生态位模型表明，弗里敦半岛受限种群因不适宜的栖息地与其他种群分隔开来。
OTU的地理隔离以及与其他蛙科物种水平分化相当的分子差异表明，游泳齿蟾包含隐存物种多样性。各自的分布模式很可能是由于进化时间尺度上森林覆盖的反复变化（收缩和扩张）所致。在多个较干旱时期持续存在的森林避难所内的生存以及随后在较湿润时期的扩散，可能最能解释所观察到的OTU的地理分布。根据世界自然保护联盟红色名录范围标准，每个OTU都应被归类为“濒危”。如果弗里敦半岛的“游泳齿蟾”种群被认定为一个独特的物种，那么它将有理由被认定为“极度濒危”。隐存谱系的识别凸显了保护这些青蛙的迫切需求，它们均为上几内亚生物多样性热点地区内小范围的特有物种。
