Meeting Abstract
Xenopus is an excellent system for investigating how structure and function of peripheral effectors can shape behavior outputs in species- and sex- specific fashions. Most Xenopus species produce vocalizations that are sexually dimorphic in temporal structure and inter-pulse interval (IPIs); male call IPIs are typically shorter than female call IPIs, or female calls are absent altogether. In most species investigated, laryngeal muscle fiber type is sexually dimorphic and supports vocal sex differences; male laryngeal muscle is composed of fast twitch fibers, while female laryngeal muscle contains both fast and slow twitch fibers. A subset of Xenopus species including X. borealis and X. muelleri have reduced vocal sex differences; IPIs do not differ between sexes, and are longer than those of other species. We have shown previously that X. borealis laryngeal muscle contains fast and slow twitch fibers in both sexes, suggesting that the sexually differentiated laryngeal muscle fiber type characteristic of other species has been lost in X. borealis. In this study, we asked whether loss of a sexually differentiated fiber type is unique to X. borealis or shared with X. muelleri, a closely related species with reduced vocal sex differences. General laryngeal features, such as mass, is sexually dimorphic in X. muelleri. ATPase histochemistry under acidic preincubation conditions suggest a mixture of acid-sensitive and acid-stable fibers in male and female laryngeal muscle (indicating a mixed twitch type). Our present findings suggest that evolutionary loss of a sexually differentiated fiber type may be common to species closely related to X. borealis.
