Novel phylogenetic relationships of the enigmatic brevicipitine and scaphiophrynine toads as revealed by sequences from the nuclear Rag-1 gene

摘要

Owing to a general paucity of characters and an apparently high level of homoplasy, the systematics of frogs have remained disputed. A phylogeny based on the single-copy nuclear Rag-1 gene revealed unexpected placements of scaphiophrynine and brevicipitine toads. The former have usually been considered as sister group to all other extant microhylids or are even classified as a separate family. Their basal position among microhylids was weakly indicated in our analysis; but they clearly are part of a strongly supported clade composed of representatives from five other microhylid subfamilies. By contrast, the brevicipitines, a group that hitherto was unanimously considered to belong to the Microhylidae, were highly divergent and placed as a sister group to the arthroleptoid clade. These novel phylogenetic placements are best reflected by a classificatory status of the Scaphiophryninae as a subfamily of the Microhylidae, whereas the brevicipitines may merit recognition as a distinct family. Our findings seem to corroborate a high degree of morphological homoplasy in frogs and suggest that even highly derived morphological states, such as the hydrostatic tongue of microhylids, hemisotids and brevicipitines, may be subject to convergent evolution, parallelism or character reversal.