Submitted to: PLoS One
Publication Type: Peer reviewed journal
Publication Acceptance Date: 3/13/2012
Publication Date: 4/10/2012
Publication URL: http://handle.nal.usda.gov/10113/55880
Citation: Zimkus, B., Lawson, L.P., Loader, S., Hanken, J. 2012. Terrestrialization, miniaturization and rates of diversification in African frogs (Anura: Phrynobatrachidae). PLoS One. 7(4):1-11. Interpretive Summary: This project investigates the genus Phrynobatrachus (a pan African genus of mostly aquatic species of frogs with a number of land-adapted species). It is a poorly understood genus because of the remoteness of many collecting sites in Africa and the difficulty of discerning novel species when many specimens look remarkably similar. The lead author (Zimkus) has focused on this genus for her dissertation work. A Scientist (Lawson) at the Center for Medical, Agricultural, and Veterinary Entomology, USDA-ARS, Gainesville, Florida along with scientists from Harvard University and the University of Basel (Switzerland), completed a molecular, spatial, and phenotypic study of these frogs to determine whether or not miniaturization and/or terrestrialization functioned as a “key innovation” allowing for the genus to accelerate in species growth. One famous example of a key innovation is the development of feathers in birds (leading to an explosion of species).
Technical Abstract: Terrestrialization, the evolution of non-aquatic oviposition, and miniaturization, the evolution of tiny adult body size, have been identified as a key features in the evolution of modern amphibians. This study examines anuran terrestrialization and miniaturization in a phylogenetic context to determine the number of times that each has occurred within the species-rich sub-Saharan puddle frogs (Phrynobatrachus) to test whether the morphological and ecological traits associated with these two trends are correlated. We use relative dating techniques to ascertain whether specific shifts in character traits are associated with increased diversification rates and determine if a single temporal event can explain the evolution of those traits. Phrynobatrachus independently evolved alternate, terrestrial reproductive modes at least seven times, including terrestrial deposition of eggs and terrestrial, non-feeding larvae. Reproductive terrestrialization is linked to a decrease in diversification rates compared to lineages with aquatic reproduction. The originations of these independent shifts are not linked to a common geological or climatic event but instead are distributed randomly through phylogenetic and geographic space. Body size within Phrynobatrachus ranges in size from 12 mm to greater than 50 mm. Phylogenetic reconstruction showed that each of the three major clades of puddle frogs follows a trend of reduction of both body size and pedal webbing, and these two traits are highly correlated. Osteological changes correlated with body size reduction include those with a phylogenetic signal (fusion of carpal, or wrist, elements—from six separate bones to four) and those coupled with truncation of development (asymmetric loss or duplication of phalanges).