Sexual Dimorphism and Female Reproductive Characteristics in the Hainan Water Skink (Tropidophorus hainanus) from Hainan, South China

We studied sexual dimorphism in body size and shape and female reproductive characteristics in the Hainan Water Skink (Tropidophorus hainanus) from Hainan, South China. In our sample the largest female and male were 61.1 and 55.2 mm snout-vent length (SVL), respectively. The mean SVL was larger in adult females (52.0 mm) than in adult males (48.3 mm). Juveniles were sexually dimorphic in head length but not in other examined morphological variables. Adult males were longer in head length and shorter in abdomen length and fore-limb length than adult females of the same SVL. Ontogenetic shifts in sexual dimorphism in body shape were evident, as revealed by the fact that morphological differences between the sexes were more pronounced in adults than in juveniles. Females produced a single litter of 3-6 offspring per season from early August to early September. Litter size, litter mass and offspring (neonate) mass were positively related to female SVL. Neonate mass was independent of relative fecundity. From the above findings we draw three main conclusions. First, females are the larger sex in T. hainanus, and sexual dimorphism in body shape is more pronounced in adults than in juveniles. Second, larger female T. hainanus produce more and larger offspring and thus heavier litters than smaller ones. Third, the offspring size-number trade-off is not evident in T. hainanus.