Evolutionary history of secondary sexual characters in the most species-rich genus of anurans, the direct-developing frogs of the genusPristimantis(Anura: Strabomantidae)

Abstract

Ancestral character-state reconstruction is a powerful method in phylogenetics that can be applied to elucidate the evolutionary history of secondary sexual characters. Here, we surveyed the variation and reconstructed the ancestral states of secondary sexual characters (i.e. sexual dichromatism, vocal slits and nuptial pads) for the most species-rich genus of anurans (Pristimantis) using maximum parsimony, maximum-likelihood and Bayesian methods. This study demonstrates that at least five independent transformation series account for the occurrence of sexual dichromatism in Pristimantis: dorsum, throat, venter, groin and posterior surface of thighs. The ancestral reconstructions suggest that the most recent common ancestor of Pristimantis lacks sexual dichromatism on these five body areas. Likewise, the occurrence of vocal slits and the absence of nuptial pads were inferred as ancestral conditions. Morphological synapomorphies were identified for Yunganastes and two infrageneric units within Pristimantis (the Pristimantis devillei and Pristimantis unistrigatus species groups). Our results demonstrate that the evolutionary history of the secondary sexual characters in Pristimantis followed a rather complex pattern of multiple independent gains and losses for which this genus is a promising model to investigate the evolution of secondary sexual characters in the context of the complex interactions between natural and sexual selection.

A cretaceous frog with eggs from northwestern China provides fossil evidence for sexual maturity preceding skeletal maturity in anurans

“…The stage at which sexual maturity occurs greatly influences fitness and is a critical transition in the life history of organisms [24][25][26]. In extant species, this stage is most often determined by gonadal characteristics or external secondary sexual traits [27], although skeletochronology has also been applied to determine the relative age of anurans and other vertebrates [28][29][30]. However, in the case of fossils most of these approaches are typically hindered by incomplete preservation of body parts.…”