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Arthroleptidae are an ecologically diverse group of sub-Saharan frogs. Arthroleptid tadpoles predominately occur in slow flowing to torrent waters. Their musculoskeletal system and the relationship between tadpole morphology and lifestyle are poorly understood. Here, we investigated the cranial morphology of four arthroleptid tadpoles occurring in different microhabitats: Leptopelis parkeri , Astylosternus occidentalis , Trichobatrachus robustus , and Nyctibates corrugatus. The crania of the tadpoles of A. occidentalis , N. corrugatus , and T. robustus are highly modified relative to L. parkeri , with wide and partly or completely fused cornua trabeculae, a fused cartilago labialis superior, as well as several modifications of the palatoquadrate, such as a broad commissura quadratocranialis and a processus ventralis which expands the surface for the origin of the large m. orbitohyoideus. The processus hyoquadratis is an evolutionary novelty, forming a functional unit together with the ceratohyale in the cranium of N. corrugatus. Finally, we compared the cranial morphology of these arthroleptids to other lotic and non-lotic species. Although the processus ventralis is not a generalized feature of the cranium in lotic species, it is not present in lentic species. [ABSTRACT FROM AUTHOR]

The African frog genera Arthroleptis and Cardioglossa are unique among vertebrates in having males with extremely long third fingers. In some species, this sexual dimorphism is impressive, with male third fingers approaching 40% of body length. However, the diversity of this trait has not been documented thoroughly and several species appear to lack this trait. The present study documents the diversity of male secondary sexual traits in Arthroleptis and Cardioglossa, including elongate third fingers and digital and inguinal spines. Furthermore, it explores hypotheses of trait evolution, including explanations for the absence of male traits. Analyses of covariance suggest that the functional relationship between finger length and snout–vent length (SVL), both within and among species, is different for male finger III than for male fingers I, II, and IV, or for female finger III. Ancestral state reconstruction suggests that all male traits were present in the most recent common ancestor of Arthroleptis and Cardioglossa and that reduction or loss of traits occurred later. Across species, independent contrast analyses find no correlation between SVL and either male relative third digit length or dimorphism in relative third digit length. The number of spines on male fingers II and III are positively correlated but spine number is not correlated with SVL and only weakly correlated with relative third digit length. The diversity of male traits is evolutionarily labile and is not explained by simple hypotheses of character evolution. Arthroleptis and Cardioglossa may thus provide an interesting study system for understanding how changes in sexual selection forces produce male trait diversity. © 2009 The Linnean Society of London, Biological Journal of the Linnean Society, 2009, 96, 553–573. [ABSTRACT FROM AUTHOR]