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Theory predicts that sexually dimorphic traits under strong sexual selection, particularly those involved with intersexual signaling, can accelerate speciation and produce bursts of diversification. Sexual dichromatism (sexual dimorphism in color) is widely used as a proxy for sexual selection and is associated with rapid diversification in several animal groups, yet studies using phylogenetic comparative methods to explicitly test for an association between sexual dichromatism and diversification have produced conflicting results. Sexual dichromatism is rare in frogs, but it is both striking and prevalent in African reed frogs, a major component of the diverse frog radiation termed Afrobatrachia. In contrast to most other vertebrates, reed frogs display female-biased dichromatism in which females undergo color transformation, often resulting in more ornate coloration in females than in males. We produce a robust phylogeny of Afrobatrachia to investigate the evolutionary origins of sexual dichromatism in this radiation and examine whether the presence of dichromatism is associated with increased rates of net diversification. We find that sexual dichromatism evolved once within hyperoliids and was followed by numerous independent reversals to monochromatism. We detect significant diversification rate heterogeneity in Afrobatrachia and find that sexually dichromatic lineages have double the average net diversification rate of monochromatic lineages. By conducting trait simulations on our empirical phylogeny, we demonstrate that our inference of trait-dependent diversification is robust. Although sexual dichromatism in hyperoliid frogs is linked to their rapid diversification and supports macroevolutionary predictions of speciation by sexual selection, the function of dichromatism in reed frogs remains unclear. We propose that reed frogs are a compelling system for studying the roles of natural and sexual selection on the evolution of sexual dichromatism across micro- and macroevolutionary timescales.

The Central African treefrog Leptopelis brevirostris has a characteristically short and vertically truncated snout, a tooth-like process at the centre of the mandible, and unlike most species of Leptopelis, eats terrestrial gastropods. Two morphologically similar species (L. crystallinoron and L. brevipes) have been described in sympatry with L. brevirostris, each on the basis of a single female specimen and then provisionally synonymised with L. brevirostris by subsequent authors. Here we re-examine the holotypes of the three species and collect both genetic (mtDNA and 25 nuDNA loci) and morphological data across the range of L. brevirostris and its sister species L. notatus to test the hypothesis that L. brevirostris is comprised of more than one species. We found that the diagnostic characters for L. crystallinoron (lacking a visible tympanum and having larger vomerine teeth in contact) and L. brevipes (distinctive dorsal colouration) are also present in L. brevirostris and L. notatus. Furthermore, these characters vary among individuals that share the same mitochondrial haplotype and that occur within a single locality, including the type locality of L. crystallinoron. Although all samples from the type locality of L. crystallinoron form a distinct mitochondrial lineage relative to L. brevipes and L. brevirostris, our analysis of 25 nuclear loci does not support this relationship and instead suggests that this mitochondrial divergence reflects phylogeographic structure across the range of L. brevirostris, including samples from the type localities of L. crystallinoron and L. brevipes. By contrast, the mitochondrial divergence between L. notatus and L. brevirostris is strongly supported in the nuDNA dataset. Consequently, we recognise both L. brevipes and L. crystallinoron as synonyms of L. brevirostris. Given the extensive variation in the colour pattern, the tympanic membrane, and the size and shape of the vomerine teeth among L. brevirostris collected from one locality, variation in these traits should be interpreted with caution in taxonomic research on Leptopelis. [ABSTRACT FROM AUTHOR]