A systematic review of Amietia vertebralis (Hewitt, 1927) and Strongylopus hymenopus (Boulenger, 1920) (Anura: Pyxicephalidae) / Jeanne Berkeljon

Abstract

For decades the taxonomic position of the Aquatic River Frog, Amietia vertebralis, and the Berg Stream Frog, Strongylopus hymenopus, has been a point of contention. A review of the literature, observations in the field and examination of preserved specimens, have led to speculation regarding the current classification of both species. Amietia vertebralis and S. hyrnenopus are highly aquatic anurans and both are endemic to the Drakensberg and Lesotho Highlands. There are a number of reasons for the inadequate information on both species, including that their initial descriptions were largely incomplete resulting in a complicated taxonomic history, and that the distribution area has been relatively poorly surveyed in terms of herpetofauna. The aim of this dissertation is to provide clarification on the taxonomic confusion associated with these two species and to determine whether possible additional related species exist (as has been suggested). To ensure that the systematic review be as comprehensive as possible, both morphological and molecular techniques were employed. External morphological characters of most available specimens of both species from institutions within South Africa, as well as type specimens from museums abroad, were examined with the aim of determining clear diagnostic I characters and to distinguish any clear trends that may indicate separate species. Because of the high level of morphological homoplasy among anurans, molecular techniques have proven invaluable in distinguishing between so-called cryptic species. Molecular analyses using both mitochondria1 DNA (16s and ND2 fragments) and nuclear DNA (RAG1 and RAG2 fragments) was conducted to determine the extent of intraspecific variation within each species, as well as their phylogenetic position in relation to each other and the African clade of pyxicephalids in which they are currently placed. Morphological assessment of museum specimens revealed a number of interesting discrepancies, especially with regard to the type and paratype specimens of both A. vertebralis and S. hymenopus. The type series of A. vertebralis appear to in fact be specimens of S. hymenopus, while the holotype of S. hymenopus (from the Natural History Museum, London) also does not match the species with which the name is currently associated. In addition, the history and label information pertaining to this specimen revealed numerous inconsistencies and conflicts with what has been recorded in the literature. In its features this specimen most closely resembles a form of Amietia fuscigula horn the Western Cape and it is suggested here that the name Strongylopus hymenopus be made incertae sedis. Statistical analysis of the morphological data confirmed the suspected differences between this holotype specimen and specimens currently identified as S. hymenopus, as well as misidentifications a number of other specimens, and corrections for these have been suggested. Furthermore, morphometric analysis confirmed that A. vertebralis and S. hymenopus are very similar in terms of their body proportions, explaining, to some extent, why these species have sometimes been confused with one another. Similarly, the molecular analysis produced some unexpected findings. Very little genetic variation was found to occur in A. vertebralis throughout its distribution, thus dispelling the hypothesis that additional species exist. Importantly, S. hymenopus was found not to be monophyletic with the Strongylopus genus, but rather to be a sister species to A. vertebralis. Together, A. vertebralis and S. hymenopus forrn a clade with Amietia sensu Frost (2006). In conclusion, name changes are suggested for both species, so that Amietia vertebralis is referred to as Amietia umbraculata and Strongylopus hymenopus becomes Amietia vertebralis. The current study adopts the nomenclature proposed by Frost et al., 2006. Please note that, for ease of discussion, throughout this study both of the taxa under review are referred to by the names by which they are currently known, i.e. Amietia vertebralis and Strongylopus hymenopus. The concluding chapter discusses the nomenclatural changes that are necessary to correct the current taxonomy and the justification for these.