The Chinese skink ( Eumeces chinensis) is sexually dimorphic in both body size and head size,and males are the larger.A comprehensive analysis of the ecological and evolutionary sources of sex differences in growth and size of head requires a detailed understanding of growth trajectories during ontogeny.Here,we pay particular attention to the point during ontogeny at which males and females diverge.Hatchlings (newly emerged young) and juveniles smaller than 70 mm SVL do not exhibit sexual dimorphism in head size,whereas males and females larger than 70mm SVL begin to diverge.The sexual dimorphism in head size is much more pronounced in adults than in juveniles sharing this character.Adult females partition relatively less resources into head growth but more into carcass growth,thereby leaving a larger space for eggs so as to increase reproductive output.Adult males,on the contrary,partition relatively more resources into head growth,thereby increasing their reproductive success and enhancing their ability to defend predators.Skinks at different ontogenetic stages slightly differ in food niche width and breadth.However,no direct evidence shows a substantial contribution of the divergence in head size to the segregation of food niche between males and females.Our results indicate that sexual selection is the main evolutionary source of sexual dimorphism in body and head sizes in E.chinensis .
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