Filling the gaps: The mitogenomes of Afrotropical egg-guarding frogs based on historical type material and a re-assessment of the nomenclatural status of Alexteroon Perret, 1988 (Hyperoliidae)

Abstract The African reedfrog taxon Alexteroon consists of only three described species with rather restricted geographical ranges. Although the assignment to a distinct genus is supported by multiple evidence, its position within the larger African hyperoliid radiation has been disputed. Available molecular data are scarce and the geographic records are few and scattered. The partially formalin fixed type series were previously not accessible to molecular analyses. This changed only very recently with the advancement of Next Generation Sequencing and ancient DNA techniques. Here we provide a reassessment of the current distribution and identity of all known species in this taxon based on (a) historical and new records, (b) morphological reanalyses of the type material and newly collected specimens from Angola and Gabon, and (c) newly established, nearly complete mitochondrial genome data from historical type and modern non-type material. We also present a molecular phylogeny (five mitochondrial loci 12S, 16S, ND1, ND2, COI, Cytb) for 78 sequences from 75 different species of Hyperolius retrieved from GenBank and 14 newly established Alexteroon sequences. We demonstrate that Alexteroon is more widely distributed than previously thought with records from northern Angola representing major southern range extensions. Results of the quantitative morphometric analyses show that the group has a rather conserved general body plan. Therefore qualitative phenotypic features observable in live specimens appear to be more useful for ad hoc species delimitation. We found Alexteroon to be nested within Hyperolius, corroborating previous findings. However, the combination of molecular data and consistent differences observed in morphology and ecology provide strong support for the distinctiveness of this evolutionary lineage within Hyperolius sensu lato. We therefore treat Alexteroon as a subgenus of Hyperolius and argue that the large and diverse genus Hyperolius is in need of revision that may result in new generic arrangements.