Robinson James V, Shaffer Lawrence R, Hagemier Douglas D, Smatresk Neal J
Department of Biology, The University of Texas at Arlington, 76019, Arlington, TX, USA.
Oecologia. 1991 Jun;87(1):1-7. doi: 10.1007/BF00323773.
Damselfly larvae may autotomize and regenerate any of their 3 caudal lamellae. At least one missing or regenerating lamella was evident in 50.1% of field collected Ischnura posita larvae. Lamellae loss during molting is very infrequent (1 out of 117 recorded molts). Laboratory trials indicate that conspecifics remove lamellae and that this process is density dependent. The percentage of larvae losing lamellae during 24 h trials ranged from 73.5 at the highest density tested to 17.3 at the lowest density. I. posita larvae are cannibalistic. The presence of lamellae reduces an individual's chance of being cannibalized. More than twice as many final instar lamellae-less larvae were cannibalized during 24 h trials than analogous individuals having 3 lamellae at experimental initiation. Costs are also associated with lamellae autotomy. 1) Although individuals without lamellae can swim they are more reluctant to release from a wooden stalk and swim when threatened (9% release) than are larvae with lamellae (29% release). Since swimming is part of their repertoire of anti-predator behaviors this behavioral shift should be detrimental. 2) Caudal lamellae function in O uptake. Trials were conducted with larvae having and not having lamellae in an experimental horizontal oxygen gradient system. Relative to larvae without lamellae, those with lamellae preferred deeper depths at PO values greater than 70 torr. Many lamellae-less larvae distributed themselves at the water surface throughout the range of PO values tested. Differential depth distribution between larvae with and without lamellae is highly significant (P < 0.01).
豆娘幼虫可以自切并再生其3片尾鳃中的任何一片。在野外采集的尖腹灰蜻幼虫中，至少有一片缺失或正在再生的尾鳃在50.1%的个体中很明显。蜕皮过程中尾鳃丢失的情况非常罕见（在记录的117次蜕皮中仅有1次）。实验室试验表明，同种个体之间会移除尾鳃，且这个过程与密度有关。在24小时试验中，失去尾鳃的幼虫百分比从测试的最高密度时的73.5%到最低密度时的17.3%不等。尖腹灰蜻幼虫会同类相食。尾鳃的存在会降低个体被同类相食的几率。在24小时试验中，最终龄期无尾鳃的幼虫被同类相食的数量是试验开始时具有3片尾鳃的类似个体的两倍多。尾鳃自切也有代价。1）虽然没有尾鳃的个体能够游泳，但当受到威胁时，它们比有尾鳃的幼虫更不愿意从木杆上松开并游动（9%松开）（有尾鳃的幼虫为29%松开）。由于游泳是它们反捕食行为的一部分，这种行为转变应该是有害的。2）尾鳃在氧气摄取中起作用。在一个实验性水平氧气梯度系统中，对有尾鳃和无尾鳃的幼虫进行了试验。相对于无尾鳃的幼虫，有尾鳃的幼虫在氧分压值大于70托时更喜欢较深的深度。许多无尾鳃的幼虫在测试的整个氧分压值范围内都分布在水面。有尾鳃和无尾鳃幼虫之间的深度分布差异非常显著（P<0.01）。
