Abstract
A comprehensive, accurate, and revisable alpha taxonomy is crucial for biodiversity studies, but is challenging when data from reference specimens are difficult to collect or observe. However, recent technological advances can overcome some of these challenges. To illustrate this, we used modern approaches to tackle a centuries-old taxonomic enigma presented by Fraser’s Clawed Frog, Xenopus fraseri, including whether X. fraseri is different from other species, and if so, where it is situated geographically and phylogenetically. To facilitate these inferences, we used high-resolution techniques to examine morphological variation, and we generated and analyzed complete mitochondrial genome sequences from all Xenopus species, including >150-year-old type specimens. Our results demonstrate that X. fraseri is indeed distinct from other species, firmly place this species within a phylogenetic context, and identify its minimal geographic distribution in northern Ghana and northern Cameroon. These data also permit novel phylogenetic resolution into this intensively studied and biomedically important group. Xenopus fraseri was formerly thought to be a rainforest endemic placed alongside species in the amieti species group; in fact this species occurs in arid habitat on the borderlands of the Sahel, and is the smallest member of the muelleri species group. This study illustrates that the taxonomic enigma of Fraser’s frog was a combined consequence of sparse collection records, interspecies conservation and intraspecific polymorphism in external anatomy, and type specimens with unusual morphology.
Highlights
Alpha taxonomy–the discovery and naming of species–is the linchpin of our catalog of biodiversity
These findings in mind, we examined other wild-caught individuals sampled throughout the putative ranges of X. fischbergi and X. fraseri in five countries in West and Central Africa: the Democratic Republic of the Congo, Cameroon, Nigeria, Chad, and Ghana
Phylogenetic analysis of partial mitochondrial DNA Sanger sequences from these individuals combined with the mitochondrial genome sequences described above demonstrates that X. fraseri is distributed in northern Ghana and northern Cameroon, including CAS 146198, whereas X. fischbergi occurs in the Democratic Republic of the Congo, Chad, and Nigeria
Summary
Targeted high-throughput sequencing of mitochondrial genomesWe used targeted high-throughput sequencing to obtain complete or almost complete mitochondrial genome sequences from all Xenopus species, including both of the ~170-year-old type specimens of X. fraseri. A fourth museum specimen (MZUF 16294) was probably initially preserved with formalin; a sample of muscle tissue from this specimen was used. This specimen was included because the morphology was unusual for this locality because the specimen has claws on three toes of each hind foot, but the only known species in Eritrea–X. clivii–has four (including one on the prehallux). This specimen served as a technical replicate for the performance of our targeted high-throughout sequencing on formalin preserved tissues
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