# Sexual Dimorphism in Three Populations of the Chiala Mountain Salamander, Batrachuperus karlschmidti (Caudata: Hynobiidae)

## TL;DR

This study examines sexual dimorphism in body shape but not size among three populations of a Chinese salamander species.

## Contribution

The study identifies sexual shape dimorphism in a hynobiid salamander species across multiple populations, linking it to sexual and fecundity selection.

## Key findings

- Sexual dimorphism was observed in body shape but not body size in Batrachuperus karlschmidti.
- Males had larger head and limb dimensions, while females had a larger interlimb distance.
- Population differences in sexual shape dimorphism may result from varying environmental selection pressures.

## Abstract

In the present study, we explored the sexual dimorphism in size and shape in three populations of Batrachuperus karlschmidti, a hynobiid species endemic to China. The results revealed that B. karlschmidti exhibited obvious sexual dimorphism in body shape, but not in body size. The observed sexual shape dimorphism could be explained by the sexual selection and fecundity selection hypotheses. This study represents one of the few reported examples of sexual dimorphism among hynobiid salamander populations.

Sexual dimorphism (SD) is a widespread phenomenon among animals and has attracted considerable interest in evolutionary biology. Most studies on SD have been limited to a single population, and few have focused on multiple populations. In this study, size and shape SD were evaluated in three populations of Batrachuperus karlschmidti, a hynobiid species endemic to China. SD was not found in body size, but was observed in body shape. Males had larger relative dimensions in head length, head width, forelimb length, forelimb width, hindlimb length, hindlimb width, and tail length. Conversely, females were larger in the relative dimension of interlimb distance. Sexual selection can account for SD in head and limbs, thereby enhancing male reproductive success. Conversely, fecundity selection drives SD in limbs, tail length, and interlimb distance, ultimately improving the reproductive ability of both sexes. Differences in sexual shape dimorphism (SShD) traits were also found among populations, which may be caused by dissimilar levels of selection forces in the environment. This study provides insight into identifying the causes that promote sexual dimorphism, as well as the degree of difference in SShD traits among populations.