Evolution of anuran foam nest: trait conservatism and lineage diversification

Pereira et al. (2017) – Biological Journal of the Linnean Society

Key innovations are organismal traits that trigger adaptive radiation and lineage diversification. The wide range of anurans’ reproductive strategies from aquatic to terrestrial modes are potential key innovations. One such strategy is the foam nest, a structure with multiple functions that originated independently several times in distinct continents. Here we explore several evolutionary aspects associated with foam nest in multiple lineages to test the hypothesis that this trait is phylogenetically conserved and has influenced diversification. We used the most inclusive anuran phylogeny to date to reconstruct ancestral states, measure phylogenetic signal and evaluate models of trait-dependent diversification. Our results show that foam nest appeared during the Paleocene-Eocene transition (c. 55 Myr) in three major groups (Leptodactylidae, Limnodynastidae and Rhacophoridae) and has been highly conserved ever since. The foam nest probably originated from an ancestor with aquatic reproduction, except in Rhacophoridae, in which it evolved from an ancestor with jelly nests. Despite possessing several ecological functions, we only found evidence of foam nest influence on diversification rates in the South American lineage Leptodactylidae. We suggest that foam nest was an important adaptation for lineages to survive through historical climatic changes and to reproduce in dry open areas.