断尾对蓝尾石龙子能量储存和运动表现的影响

Effect of tail loss on energy stores and locomotor performance in the blue-tailed skink,Eumeces elegans

在许多蜥蜴种类中,尾自切是一种主要的逃避天敌捕食的防御性策略。虽然断尾使蜥蜴获得短期的生存利益,但同时也需为此承受多方面的代价。利用从丽水采集的117条蓝尾石龙子来评价该种动物断尾的能量和运动代价。81条(约69%)石龙子至少经历过1次尾自切。断尾个体中,原先断尾事件的发生频率在不同尾区间存在显著差别,但两性间无差别。将实验组17条具完整尾的石龙子依次切去3个尾段,然后测定断尾前后石龙子的运动表现以及每个尾段、身体各部分中的脂肪含量。另15条具完整尾的石龙子作为对照组,仅测量其运动表现。尾部的脂肪含量与尾基部宽呈正相关,说明具较粗尾部的石龙子一般具有相当较多的尾部储能。尾部脂肪含量随尾长呈非等比例分布,大部分脂肪集中于尾近基部端。断尾几乎不影响蓝尾石龙子的运动表现,仅当大部分尾部被切除时疾跑速有较小程度的降低。显示了蓝尾石龙子因遭遇天敌捕食攻击或其它因素作用而产生的部分断尾可能并不会导致严重的能量和运动代价。由于野外种群蓝尾石龙子个体的断尾情况主要发生在尾近基部或中部位置,因此可以认为自然条件下该种动物的尾自切通常会遭受明显的能量和运动代价。

Tail autotomy is a major defensive strategy to escape from predation in many species of lizards. Although tail loss provides an immediate survival benefit,it may entail substantial costs. A total of 117 blue-tailed skinks （Eumeces elegans） were collected from a population in Lishui to evaluate energetic and locomotor costs of tail loss. Of the 117 skinks,81 （c. 69%） had autotomized some portion of the tail at least once. The blue-tailed skink in this population showed a high tail-break frequency,and therefore may be subjected to intense predation pressure. The proportions of individuals with tail breaks located in the proximal （except for the extreme base,10% original tail length）,middle and distal portions of tails were 47%,36% and 11%,respectively. The frequency distribution of locations of the tail break did not differ between the sexes. Three tail segments were successively removed from each of the 17 experimental skinks （14 males,3 females） initially having intact tails. Locomotor performance of each skink at the body temperature of 30℃ before and after each tail-removing treatment was measured by chasing them down the length of a 2 m racetrack with one side transparent,which allows lateral filmation with a digital video camera. The recorded tapes were later examined for three locomotor variables （the maximal distance,number of stops and sprint speed）. All removed tail segment and body components were individually weighed and determined for the amount of lipids in each sample. Another independent sample of 15 individuals （12 males,3 females） with intact tails was measured for locomotor performance to serve as controls for successive measurements taken at the time for the experimental skinks. The tail is an important storage organ for lipids in E. elegans. The amount of caudal lipid represented approximately 39% of the total body lipid,and was positively correlated with tailbase width,indicating that thicker tails contained relatively more lipids than did thinner tails. Caudal lipids were disproportionately stored along the length of the tail,with most lipids being concentrated in its proximal portion. Locomotor performance was almost unaffected by tail loss in this species,with a slight decrease in sprint speed until most of the tail was removed,and no significantly changes in the maximal length and number of stops after each tail-removing treatment. The degree of locomotor impairment associated with tail loss in this study （reduced by approximately 19% of the mean speed of skinks with intact tails） falls within the values reported for other species of lizards,thus E. elegans is among species of lizards whose tails play an important functional role in locomotion. The results from this study show that partial tail loss due to predatory encounters or other factors may not severely affect energy stores or locomotor performance in E. elegans. As tail breaks occurred more frequently in the proximal and middle portion of the tails in E. elegans collected from the field,it can be concluded that tail autotomy occurring in nature often incurs substantial energetic and locomotor costs in E. elegans.