| Studying the relationship between morphological characteristics and environment adaption of animals has been one of contains of evolution biology. Bite force capacities may be tightly linked to both the type and magnitude of the ecological challenges of food acquisition, mate acquisition, territory acquisition and antipredation in vertebrates. Bite forece of lizards had been reported widely in abroad, but no study was found in China. Shinisaurus crocodilurus is a National Class I protected animal in China, and has important scientific value in evolutionary and systematic biology. In this paper, we studied the relationship between bite force and sexual dimorphism in Shinisaurus crocodilurus, and studied the function of bite force in the maximun ranges of activity competition for understanding the cause of the sexual dimorphism and effect mechanism of bite force. This study is the basis for further studies on reproductive output, reproductive value, territory behavior and biomechanics of Shinisaurus crocodilurus1. Sexual dimorphism of Shinisaurus crocodilurusWe studied the sexual dimorphism of Shinisaurus crocodilurus through comparing body size and head size among female, male and juveniles. The results show that the ventral color of head and breast between male and female is different, it is vivid red or light blue for male and light yellow or light red for female. The head size (including head width (HW) and head length (HL)) of male is significantly larger than that of female (HL, P<0.01; HW, P<0.01), and abdomen length (AL) of female is significantly longer than that of male (P=0.018). However, the snout-vent length (SVL) and tail length (TL) between male and female are not significantly different (for SVL, P=0.193; for TL, P=0.22). The increasing rate of head length with SVL for juveniles was higher than that for females (P=0.021), whereas the head width was not significantly different between juveniles and females (P=0.545). Both the head size (including head length and head width) of juveniles and males increased with SVL at the same rate (for HL, P=0.252, for HW, P=0.441). When SVL was kept constant, head width of juveniles was larger than that of females (P<0.01) and head length of juveniles was larger than that of males (P<0.01), but the head width between juveniles and males was not significantly different (P>0.05). The results indicated that partial sexual dimorphism existed in Shinisaurus crocodilurus.2. Bite force and its influencing factors in Shinisaurus crocodilurusSignificant differences in bite force were observed among different sex and age groups (F2.88=161.303, P<0.01), the bite force of adult males (14.74±0.16N) was significantly higher than that of adult females (13.55±0.26N) (P=0.003), Both of male and females were significantly higher than that of juveniles (9.17±0.25N) (both P<0.01).A multiple regression analysis (stepwise) showed that lower jaw length was the first effect factor for bite force in the significant mode(R=0.547, P<0.01), and the head length was the second effect factor(R=0.299, P=0.002). Analyses of covariance with residual lower jaw length as the covariate demonstrated that adult males had significantly larger bite force than adult females (ANCOVA:BF—F1,54=9.896,P=0.003). When the relationships of only head shape (head length,head width, head heigth) and bite force in adult Shinisaurus crocodilurus were analyzed, results of analyses of covariance with residual head shape and snout-vent length as the covariate showed that increase with the head length (slopes:F1,54=0.084, P=0.773, intercept:F1,54=5.530, P=0.023), head width (slopes:F1,54=0.014,P=0.908, intercept:F1,54=10.109,P=0.002) and head heigth (slopes:F1,54=0.504,P=0.480, intercept:F1,54=10.304, P=0.002) the bite force increased at the same time, and the bite force of adult male was larger than that of adult females. In a word, the bite force of adult male is larger than that of adult female in Shinisaurus crocodiluru, and the lower jaw length and the head length were highly correlated with bite force.3. The relationship between activity area and bite force in Shinisaurus crocodilurusDuring June and Auguest,2010, we recorded the maximum range of activities and daily activity area, and tested the bite force of Shinisaurus crocodilurus which were reared in six captive pools in Luokeng Nature Reserve in Guangdong Province, and we studied the relationship between the home ranges and bite force. The results showed:①There was significant difference in daily activity area of the same individual (P<0.05); ANOVA multiple comparison showed that both daily activity areas of adult male and female among six pools were not different (for male F5,235=1.777,P=0.118; for female F5,233=1.827,P=0.108).②The results of One-way ANOVA showed that the daily activity areas among juveniles(3.14±0.21 m2), adult males(2.56±0.13m2) and adult females(2.03±0.12 m2)were significant different F2,47=12.670, P<0.001), and that of adult males was larger than that of adult females (P=0.031), and that of juveniles was larger than that of adult females (P<0.01) and adult males (P=0.028). The maximum range of activity areas of different age and sex groups were also significant different (F2,47=5.807, P=0.006), and that of adult males (8.77±0.22 m2) was larger than that of adult females (7.54±0.40m2) (P=0.034), that of juveniles(9.22±0.46m2) was larger than that of adult females (P=0.008), but the maximum range of activity between adult males and juveniles were not differece (P=0.686).③There were a large home range overlap in the same pool.④Regression analysis showed that only bite force (x) was positive correlative with the range of activity(y) (P=0.028,R=0.516, the Regression equation was:y=0.5898x+0.0958). The maximum range of activities (y) and the daily activity area (x) correlated significantly, the Regression equation was:Y= 0.816X+6.5526.(R2=0.1364, P<0.05)... |
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