Sexual Dimorphism in Body Size and Head Size and Female Reproduction in A Viviparous Skink,Sphenomorphus indicus

We report data on sexual dimorphism in body size and head size and female reproduction for Sphenomorphus indicus from Hangzhou,Zhejiang,eastern China.The skink is sexually dimorphic in both body and head size,and females are larger in body size but smaller in head size.Except for neonates that did not exhibit sexual dimorphism in head size,males had larger heads than did females.When SVL was kept constant,we found that juvenile and adult males did not differ in head size but juvenile females had larger heads than did adult females.Heads of neonates were relatively the largest,implying the importance of larger heads for an individuals ability to use larger prey.The smallest reproductive female was 67.7 mm SVL,and all females larger than this size produced a single litter per season.Litter size,litter mass and neonate mass varied from 3 to 11 (mean=7.2) offspring,1.30 to 5.19 (mean=3.34) g and 0.36 to 0.58 (mean=0.48) g,respectively.Litter size determined by counting the number of yolked follicles and oviductal eggs outnumbered that by counting the number of neonates by 1.0 offspring.Neonate mass was independent of maternal SVL,and litter size was independent of maternal conditions.Both litter size and litter mass were positively correlated with maternal SVL,and there was a marginally positive correlation between relative clutch mass and maternal SVL.An inverse relationship between neonate mass and litter size was found in S.indicus,suggesting a trade-off between the two variables.Our data indicate that selection should favor larger body size in S.indicus,as females can increase their reproductive output through production of more offspring by increasing body size.Moreover,adult females partition relatively less resources into head growth but more into carcass growth,thereby leaving a larger space for producing more offspring.