Terrestrialization, Miniaturization and Rates of Diversification in African Puddle Frogs (Anura: Phrynobatrachidae)

Abstract

Terrestrialization, the evolution of non-aquatic oviposition, and miniaturization, the evolution of tiny adult body size, are recurring trends in amphibian evolution, but the relationships among the traits that characterize these phenomena are not well understood. Furthermore, these traits have been identified as possible “key innovations” that are predicted to increase rates of speciation in those lineages in which they evolve. We examine terrestrialization and miniaturization in sub-Saharan puddle frogs (Phrynobatrachidae) in a phylogenetic context to investigate the relationship between adaptation and diversification through time. We use relative dating techniques to ascertain if character trait shifts are associated with increased diversification rates, and we evaluate the likelihood that a single temporal event can explain the evolution of those traits. Results indicate alternate reproductive modes evolved independently in Phrynobatrachus at least seven times, including terrestrial deposition of eggs and terrestrial, non-feeding larvae. These shifts towards alternate reproductive modes are not linked to a common temporal event. Contrary to the “key innovations” hypothesis, clades that exhibit alternate reproductive modes have lower diversification rates than those that deposit eggs aquatically. Adult habitat, pedal webbing and body size have no effect on diversification rates. Though these traits putatively identified as key innovations for Phrynobatrachus do not seem to be associated with increased speciation rates, they may still provide opportunities to extend into new niches, thus increasing overall diversity.

A new minute species of Pristimantis (Amphibia: Anura: Craugastoridae) with a large head from the Yanachaga-Chemillén National Park in central Peru, with comments on the phylogenetic diversity of Pristimantis occurring in the Cordillera Yanachaga

“…Miniaturization of frogs has been documented in many species of different families (Wells 2007;Zimkus et al 2012), and miniaturized frogs often have lost (e.g., digits) or reduced (e.g., phalanges) elements of (Yeh 2002). Body proportions of P. boucephalus sp.…”

Biological Scaling Problems and Solutions in Amphibians

“…Miniaturization has been documented in all three clades, and occurred independently many times during evolution. Although their size makes the smallest amphibians vulnerable to more predators, including insects (Rittmeyer et al 2012), it also enables them to hide more easily, exploit alternate food sources, use physically smaller niches, and attain reproductive ability at an earlier age (Zimkus et al 2012). In contrast, the endothermic metabolism of birds and mammals dictates a larger minimum adult body size.…”

High resolution images for Phylogeny, taxonomic revision, and character evolution of the genera Chiasmocleis and Syncope (Anura, Microhylidae) in Amazonia, with descriptions of three new species.

“…Miniaturization and ''terrestrialization'' (i.e., evolution of endotrophic tadpoles or direct development) have been associated with higher rates of diversification and evolutionary success in frogs, including cophyline (Andreone et al, 2005) and asterophryine (Zweifel, 1972) microhylids, although empirical tests did not find this to be correct in all cases (Gomez-Mestre et al, 2012;Zimkus et al, 2012). It appears that this is also not the case for New World microhylids.…”