Convergent evolution in the unique and bizarre buccopharyngeal morphology of sand-eating Malagasy tadpoles (Anura: Mantellidae).

Convergent evolution, the independent evolution of homoplastic character-states, is a widespread phenomenon in the tree of life. Although convergence has been documented in several groups, instances of convergent evolution in syntopic lineages are rare. Herein we report the convergent evolution in sand-eating mantellid tadpoles inhabiting the same streams in Madagascar. We investigated the morphology of the oral apparatus and buccopharyngeal cavity in several lineages of mantellids, focusing on sand-eating tadpoles of the genera Mantidactylus and Boophis. Additionally, we investigated the patterns of stream occupation by these tadpoles in 66 assemblages in Madagascar. We performed a parsimony total evidence analysis of DNA and phenotypic characters using direct optimization of the DNA sequences with PhyG. In our optimal hypothesis, sand-eating tadpoles evolved independently three times within Mantellidae. Most larvae are characterized by the presence of unique ruffled ridges in the buccopharyngeal cavity, although the distribution of these ridges on the buccal roof and floor, as well as characters from the oral disc, can vary independently in these lineages. The co-occurrence of all sand-eating tadpoles in the studied assemblages reveals an intriguing and interesting pattern of convergent evolution in syntopic species. Hence, we discuss the possible mechanisms of niche differentiation and resource exploitation.