Abstract
BackgroundCorrect 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.ResultsOur 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.ConclusionGeographic 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.Electronic supplementary materialThe online version of this article (doi:10.1186/s12862-015-0346-9) contains supplementary material, which is available to authorized users.
Highlights
Correct species identification is crucial in different fields of biology, and in conservation
The tree topology resulting from 3527 bp concatenated mitochondrial and nuclear genes, with respective node support values, is shown in Figure 1a
The mitochondrial 16S rRNA (16S) gene is commonly used for barcoding approaches in anuran amphibians [29,30,48], and uncorrected p-distances recognized between operational taxonomic units (OTU) are comparable to species level differences in nonrelated frog genera and families pointing to cryptic speciation in Odontobatrachus
Summary
Correct species identification is crucial in different fields of biology, and in conservation. Understudied cryptic species complexes may lead to inaccurate scientific results in studies of community ecology [11,12], population assessments in economically exploited species [13], or conservation decisions aimed at retaining phylogenetic diversity [14]. Improved methodologies, such as molecular and acoustic techniques, make biologists increasingly aware of cryptic species and related problems (e.g. the lack of reliable morphological features for identification [10,15,16]). These may comprise inconspicuous taxa in pathogenic fungi [18], bryophytes [19], insects [20], small mammals [15,21], birds [1], or reptiles [22], but may include charismatic organisms such as hammerhead sharks [23], lemurs [24], giraffes [25], and elephants [26]
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