Climatic correlates of female and male reproductive cycles and plasma steroid hormone levels in the many-lined sun skink Eutropis multifasciata

Abstract

Gonadal activity and plasma steroid hormone (testosterone and 17β-estradiol) levels in males and females of a viviparous skink (Eutropis multifasciata) were investigated. Changes in the hormone profiles were then correlated to changes in environmental factors such as temperature and rainfall and were found to vary seasonally in both sexes. Gonadal activity, calculated using testicular mass and volume, seminiferous tubule diameter and epithelial height in males and, in females, ovary mass and largest follicular volume also varied seasonally. Peak spermiogenesis was in synchrony with maximal vitellogenic activity, but reproductive synchronicity among females was low. Ovary mass and largest follicular volumes were negatively related to air temperature and rainfall. Testicular mass and volume were not related to air temperature, but both were negatively related to rainfall. Rainfall explained a greater proportion of variation in vitellogenic activity than temperature. As for the climatic correlates of seasonal variation in plasma steroid hormones, we found only in males that the plasma level of testosterone was negatively related to rainfall. Taken together, our data show that male and female reproductive activities are more tightly correlated with rainfall than temperature in E. multifasciata.