Submitted to: Molecular Ecology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 12/20/2012
Publication Date: 2/4/2013
Citation: Lawson, L.P., Bates, J.M. 2013. Diversification within the Spiny Throated Reed Frog complex (H. tanneri and H. minutissimus, H. spinigularis): untangling evolutionary history among closely related lineages. Molecular Ecology. 22:1947-1960. Interpretive Summary: The genus of African Reed Frogs (Hyperolius) is a complex and little understood group of amphibians with a diverse distribution throughout sub-Saharan Africa. In light of global amphibian declines, most pronounced in tropical highland areas, this study illuminates the diversity and mechanisms of differentiation within a species complex of montane Hyperolius (the Spiny-Throated Reed Frog complex). A Scientist at the Center for Medical, Agricultural, and Veterinary Entomology, USDA-ARS, Gainesville, Florida and a scientist from the Field Museum of Natural History, Chicago, IL, completed a molecular, spatial, and phenotypic study of these frogs to understand historic differentiation and species status. Additionally, vulnerability of each proposed species to habitat loss and local extinction in the near future was investigated. This dataset helps to quantify the natural diversity within the system, a critical component for protecting this diversity through changing climate conditions and human pressures. This work is part of the dissertation research for Lawson before joining USDA-ARS.
Technical Abstract: Super-species complexes, where lineages are morphological similarity but evolutionary divergent, are a particularly interesting biological phenomena in terms of understanding the process of diversification. The signal of selection is less swamped by secondary divergence and spatial relocation than in more clearly divergent groups. The spiny-throated reed frog complex (Hyperolius spinigularis, H. tanneri, H. minutissimus) is comprised of morphologically similar populations occupying isolated mountaintops in East Africa. This system was used to investigate how distance, adaptation, and competition generated and maintains diversity, particularly in regards to the spatially disjunct populations within the spiny-throated reed frogs. To address this, we created a multi-locus molecular dataset to reconstruct the phylogeographic and biogeographic history of this lineage, and combined it with spatial information, environmental niche modeling, paleoclimate reconstructions, and morphological analyses. This combination allowed us to determine biotic and abiotic processes involved in diversification within this group. Strong disagreement was found between mitochondrial and nuclear gene trees, with mitochondrial DNA supporting the monophyly of the northern Tanzanian taxa (H. spinigularis Tanzania + H. tanneri) to the exclusion of the southern Malawian H. spinigularis, and nuclear genes supporting the monophyly of H. spinigularis from Tanzania and Malawi. We believe this mismatch is a case of mitochondrial capture of H. spinigularis mtDNA into H. tanneri from an ancient hybridization event. Reconstructions of ancestral distributions show the history to be driven by vicariance between the three morphological lineages, long distance dispersal between H. spinigularis from northern Tanzania and southern Malawi, and possibly competitive exclusion and prezygotic mating barriers between adjacent H. tanneri and H. spinigularis populations. Morphometric data and environmental niche requirements imply that adaptation to divergent climatic conditions in allopatry and parapatry also has been a factor in diversification of these frogs.