蓝尾石龙子的头部两性异形和食性

通过测量头、体大小和胃检研究浙江泰顺产蓝尾石龙子 (Eumeceselegans)个体发育过程中两性异形和食性的变化。蓝尾石龙子成体个体大小和头部大小的两性差异显著 ,雄性大于雌性。不同发育阶段雌性头长与SVL的线性回归斜率无显著差异 ,头宽与SVL线性回归斜率的差异显著 ,成体和SVL <5 0mm幼体头宽随SVL的增长速率显著小于SVL为 5 0 - 6 9mm的幼体。雄性头部相对于SVL呈加速式异速生长。两性比较发现 :雌雄幼体头长和头宽随SVL的增长速率无显著差异 ,SVL <5 0mm幼体特定SVL的头长和头宽无显著的两性差异 ,但SVL为 5 0 - 6 9mm的雄性幼体头长和头宽大于SVL相同的雌性幼体 ;雄性成体头长和头宽随SVL的增长速率显著大于雌性。SVL <5 0mm的雌性幼体头部相对小于SVL为 5 0 - 6 9mm的同性幼体 ,性成熟雌体头部相对小于SVL为 5 0 - 6 9mm的同性幼体。雌性幼体、雄性幼体、雌性成体和雄性成体食物生态位宽度分别为 12 3、 12 5、 4 8和 14 4。雌雄幼体食物生态位重叠度最高 ,雌雄成体食物生态位重叠度次之 ,成体与幼体食物生态位重叠度较小。成体摄入食饵的大小 (用胃内完整食物长度的平均值表示 )和变化范围大于幼体。两性成、幼体摄入的食饵大小差异显著。两性个体摄入的食饵大小均与其SVL呈正相关 ,表明较大

Sexual dimorphism in head size and food habits in the blue-tailed skink Eumeces elegans

We collected blue-tailed skinks Eumeces elegans during May-July 2002 and 2003 from a mountain population in Taishun, Zhejiang, with an aim to uncover the determinants of sexual dimorphism in head size. The captured skinks were preserved in 5% formalin, and were later measured and dissected to provide original data on morphology, sexual dimorphism, dietary habits and reproductive biology. The preserved specimens were measured for snout-vent length (SVL), tail length, head length (from the snout to the anterior edge of tympanum) and head width (taken at the posterior end of the mandible). After measurements, the specimens used to analyze dietary habits were opened with a mid-ventral incision, and prey items in the stomach were removed for identification and measurement. The stomach contents of each specimen were classified as animals (which were usually placed into specific taxonomic categories) or plants (primarily seeds). Relatively undigested prey items were measured for length. Sex and reproductive status were determined by visual inspection of gonads, and individuals larger than 69 mm SVL were classified as mature. Males are the larger sex, because adult males attained larger mean and maximum sizes (SVL) than females. Skinks larger than 50 mm SVL had already showed sexual dimorphism in head size (both head length and head width), with males having larger heads than females of the same body size. The differences in head size between the sexes were much more pronounced in adults than in sexually dimorphic juveniles with SVL ranging from 50 to 69 mm, largely because the ontogentic shifts in the rate at which head size increases with increasing SVL occurred in both females and males. Because adult males with larger heads have the advantage of winning the male-male contests for resources (including mates), larger heads evolved in males primarily due to the directional action of sexual selection. Unlike males, females with greater abdominal cavities may take advantage of holding more and/or larger eggs (offspring). Given that resources available to any females are limited, increasing carcass (abdomen) growth, thereby increasing reproductive output, must reduce head growth. Thus, smaller heads in adult females primarily result from the action of fecundity selection. Dietary habits shifted with body size, but did not differ significantly between the sexes of the same body size. Larger skinks were able to take larger prey and, thus, had wider food niche breadths, as compared to smaller ones. Data on ontogentic shifts in dietary habits do not provide evidence showing an important contribution of the divergence in head size to the segregation of food niche between the sexes. Thus, we conclude that sexual dimorphism in head size in Eumeces elegans is primarily determined by the ultimate factors (sexual selection for males and fecundity selection for females) rather than the proximate environmental factors and the avoidance of inter-sexual competition for food.