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.


Ancestral reconstruction of reproductive traits shows no tendency toward terrestriality in Leptodactyline frogs

Pereira et al. (2015) – BMC Evolutionary Biology

Traditionally, the evolution of terrestrial reproduction in anurans from ancestors that bred in water has been accepted in the literature. Still, the existence of intermediate stages of water dependency, such as species that lay eggs close to water (e.g., in burrows) instead of in bodies of water, supports the hypothesis of an ordered and gradual evolution in the direction of a more terrestrial form of reproduction. However, this conventional view has recently been challenged by some anurans groups. Leptodactylinae frogs are a remarkable example of anurans with an outstanding diversity in terms of reproductive features, with distinct water dependency among lineages. Here, we tested the hypothesis of a gradual and ordered tendency towards terrestriality in Leptodactylinae, including the existence of obligatory intermediate stages, such as semi-terrestrial reproductive strategies. We also addressed the association between reproductive modes and morphological and ecological features. An ancestral reconstruction analysis indicated that even though shifts from aquatic to terrestrial breeding occurred throughout the history of Leptodactylus and Adenomera, shifts from terrestrial to aquatic reproduction happened at almost the same frequency. Our results also demonstrated that reproductive modes for semi-terrestrial tadpoles were not necessarily an intermediate form between aquatic and terrestrial breeds. Correlations among reproductive modes and other life-history traits suggested that tadpole environment, clutch size, nuptial spines, and egg pigmentation were co-evolving and driven by water dependency. Our results found no evidence of evolutionary tendencies toward terrestriality in Leptodactylinae. We found reversals from terrestrial to aquatic tadpole development and no evidence of obligatory intermediate stages, such as semi-terrestrial reproductive strategies. We also found correlations between reproductive modes and other life-history traits driven by water dependence. Aquatic reproductive modes are associated with higher clutch sizes, lentic waters, and the presence of nuptial spines and egg pigmentation.