Comparative larval morphology of Madagascan toadlets of the genus Scaphiophryne: phylogenetic and taxonomic inferences.

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Abstract:

The larval morphology of Madagascan frogs of the family Microhylidae, subfamilies Dyscophinae and Scaphiophryninae, is described based on material from the genera Dyscophus (D. insularis), Paradoxophyla (P. palmata) and five species of the enigmatic genus Scaphiophryne: S. brevis, S. calcarata, S. madagascariensis, S. menabensis and S. spinosa. The latter are known to have larvae that are intermediate between the filter-feeding larval type typical for most microhylids and the generalized tadpole of most ranoid and hyloid frogs. However, the two detailed descriptions available to date, referring to Scaphiophryne calcarata and S. gottlebei, pointed to important differences in size and oral morphology within Scaphiophryne. Our data confirm that all studied Scaphiophryne have horny beaks but lack keratodonts and are to be referred to the psammonektonic ecomorphological guild. Scaphiophryne brevis and S. calcarata have rather small tadpoles (up to 22 mm total length) whereas S. madagascariensis, S. menabensis and S. spinosa, as well as S. gottlebei, have larger tadpoles (up to 48 mm total length) with a striking distance between the skin and the internal organs, giving the head and body a balloon-like appearance. These two morphological tadpole groups agree with previously published molecular phylogenetic data and support the classification of these species in the two subgenera Pseudohemisus and Scaphiophryne. The larva of the genus Paradoxophyla, the sister group of Scaphiophryne, has a typical microhylid filter-feeding morphology and shares many synapomorphies with other microhylids. Since a convergent evolution of these features is unlikely, the ancestors of Scaphiophryne appear to have re-acquired their beak and other characters that at first view are plesiomorphic.