Evolution of terrestrial breeding in African toads

Study suggest that terrestrial reproduction evolved as an adaptation to steeper and wetter habitats

Data resources used via GBIF : 13,828 species occurrences
Schismaderma carens
African split-skin toad (Schismaderma carens) by fayne via iNaturalist. Photo licensed under CC BY-NC 4.0.

Among terrestrial vertebrates, amphibians are the most reproductively diverse group, with more than 40 different reproduction strategies recognized in anurans, alone. In tropical climates especially, terrestrial breeding is common, but the factors driving the evolution of this strategy are unknown.

In this study, researchers reconstructed the most complete phylogeny of African toads (family Bufonidae) to date including 78 per cent of described species. Assigning reproductive strategies to species and examing environmental factors in effect at GBIF-mediated occurrences, the authors found that the most likely factors contributing to the evolution of terrestrial reproduction were steep slopes and low water availability.

Based on the evolutionary timing of transitioning from the dry, flat and open habitats to steeper and wetter habitats, the authors note that transition coincided with or preceeded evolution of terrestial breeding, suggesting an adaptive mode of evolution, rather than exaptation that made colonization of these new habitats possible.

Liedtke HC, Müller H, Hafner J, Penner J, Gower DJ, Mazuch T, Rödel M-O and Loader SP (2017) Terrestrial reproduction as an adaptation to steep terrain in African toads. Proceedings of the Royal Society B: Biological Sciences. The Royal Society 284(1851): 20162598. Available at: https://doi.org/10.1098/rspb.2016.2598.