不同程度的尾损伤对镇海林蛙(Rana zhenhaiensis)蝌蚪游泳速度的影响

无尾两栖类蝌蚪的尾巴通过产生强大的游泳速度在反捕食中起到了重要的作用。以镇海林蛙(Rana zhenhaiensis)蝌蚪为实验动物来评估断尾的运动代价。以74尾具有完整尾蝌蚪作为实验组,通过截去不同尾长片段,人为分成轻微尾损伤组(30%)和严重尾损伤组(30%)并测定两组蝌蚪在断尾前后的游泳速度。以16尾完整尾蝌蚪作为对照组在实验组断尾前后同时进行游泳速度的测定。实验结果显示断尾影响蝌蚪的游泳速度,但仅在尾损伤程度达到尾长的30%以上时才产生不利的影响。这表明轻微尾损伤并不对镇海林蛙蝌蚪的游泳速度产生严重影响。在断尾前后实验组蝌蚪的游泳速度均与尾长呈正相关。在相同尾长状态下,尾损伤蝌蚪的相对游泳速度明显快于完整尾蝌蚪。因此,尾损伤的镇海林蛙蝌蚪有可能通过改变尾和身体的摆动频次等方式在断尾后对游泳速度进行了一定的补偿。尾损伤在野外频繁发生于蝌蚪的尾远端,据此推测镇海林蛙蝌蚪在自然条件下的尾损伤并不会产生严重运动代价。

Effect of tail injuries of different severities on the swimming speed of larval Rana zhenhaiensis (Anura:Ranidae)

The tails of tadpoles of anuran amphibians play an important role in anti-predator behavior, as they can confer powerful swimming abilities or become a lure for shifting a predator''s attack from the body to the tail. We used Rana zhenhaiensis (Anura:Ranidae) tadpoles in the Gosner stages from G26 to G29 as a model system to evaluate the locomotor cost of tail loss in tadpoles. Two experimental groups were created based on the degree of tail-removal, defined as the ratio between the length of the tail removed and length of the tail left intact. The first experimental group, with slight tail loss (tail loss group 1) comprised manipulated tadpoles with less than 30% tail loss, and a mean value of 22% (standard deviation [SD]=0.06, N=30) tail loss; the other experimental group (tail loss group 2) comprised individuals with tail loss of more than 30%, and a mean value of 43% (SD=0.10, N=44) tail loss. The swimming speed of each individual was measured before and after tail removal. We used a digital video camera to record the swimming performance of each individual in a 50-cm straight lane. The video files were then examined using the software program Ulead Video Studio to determine the fastest swimming speed over a 10-cm interval. The control group, 16 individuals with intact tails, was measured for swimming speed to be compared to that of the tadpoles in the two experimental groups. We used repeated-measures ANOVA to analyze the swimming speed data, which indicated that tail loss affected the swimming speed of R. zhenhaiensis tadpoles, but only in some individuals with more than 30% tail loss. These results suggested that slight tail injury may not severely affect the swimming speed of R. zhenhaiensis tadpoles. Swimming speed positively correlated with tail length in individuals, both before and after tail-removal, and the swimming speed was significantly greater after tail loss. Therefore, we speculate that the swimming speeds of tadpoles with tail injuries may be partly compensated by increases in the frequency of tail and body twisting. Tail loss occurred more frequently in the distal portion of the tail tip in R. zhenhaiensis tadpoles collected from the field, and 47% of captured tadpoles had different levels of tail injury; moreover, we used the G-test to analyze different levels of tail injury in wild population of R. zhenhaiensis tadpoles, and found significant differences between our experimental groups with two different levels of tail injury. More than 94% of tadpoles have slight tail injuries, but not different among different developmental stages in the natural ponds. Thus, we conclude that R. zhenhaiensis tadpoles with tail injuries did not incur substantial locomotor costs in the wild.