Sexual Dimorphism in Morphological Traits and Food Habits in Tiger Frogs,Hoplobatrachus rugulosus in Lishui,Zhejiang

We used tiger frogs (Hoplobatrachus rugulosus) collected from Lishui (Zhejiang,eastern China) to study sexual dimorphism in morphological traits and food habits. Females larger than 80 mm SUL (snout-urostyle length) and males larger than 70 mm SUL were considered to be adults,and others to be juveniles. The frog is sexually dimorphic,with females being the larger sex. Juveniles were not sexually dimorphic in any of the examined morphological traits. Head length and hind-limb length were larger in adult females than in adult males and fore-limb length,eye diameter and tympanum diameter were larger in adult males than in adult females,when influence of variation in body size (SUL) was removed using ANCOVAs. Other examined morphological traits did not differ between adult females and adult males. The magnitude of hind-limb length deviating from the bilateral symmetry did not differ between adults and juveniles and between both sexes,whereas the magnitudes of fore-limb length deviating from the bilateral symmetry were greater in adults than in juveniles and were greater in females than in males. A principal component analysis resolved three components (with eigenvalues ?1) from ten size (SUL) free morphological variables, accounting for 64.6% of variation in the original data. The first component (26.9% variance explained) had high positive loading for size-free values of head width,eye diameter and tympanum diameter,the second component (19.7%) for size-free value of hind-limb length,and the third component (18.0%) for size-free values of interocular length and internasal length. Adult females had lower scores on the first axis of a principal component analysis than did adult males,but the score on the second and the third axes did not differ significantly between adult females and adult males. The tiger frog is an insectivorous species,but it also feeds on invertebrates other than insects. Frogs of different ages and sexes,in various degrees,differed in food niche width and breadth. However,no direct evidence shows a noticeable contribution of the divergence in head size to the segregation of food niche between males and females,which is considered to important to mitigate the competition for food between both sexes.