McPeek Mark A
Department of Biological Sciences, Dartmouth College, Hanover, New Hampshire, 03755.
Evolution. 1997 Apr;51(2):459-466. doi: 10.1111/j.1558-5646.1997.tb02433.x.
Previous studies suggest that the evolution of increased caudal lamellae size to increase swimming speed was an adaptation of Enallagma damselflies for coexisting with large, predatory dragonflies in fishless lakes. To test whether dragonfly predation still exerts selection pressures for increased lamellae size, I performed a field experiment in which I manipulated the abilities of dragonfly larvae to inflict mortality on Enallagma boreale larvae and compared differences in lamellae size and shape between treatments. In cages where dragonflies were free to forage on damselflies, surviving E. boreale larvae had lamellae that were larger in lateral surface area, and that were wider relative to their length, as compared with larvae recovered from treatments in which dragonflies were not permitted to forage on damselflies. Selection differentials of about 0.25 phenotypic standard deviation units were measured for both of these characters. These results indicate that dragonfly predation still exerts significant selection pressures on damselfly antipredator adaptations. The results of this study are discussed in the context of studies of adaptation.
先前的研究表明，尾鳃增大以提高游泳速度的进化是伊氏蟌适应在无鱼湖泊中与大型食肉蜻蜓共存的一种方式。为了测试蜻蜓捕食是否仍对鳃增大施加选择压力，我进行了一项野外实验，在实验中我操控了蜻蜓幼虫对北方伊氏蟌幼虫造成死亡的能力，并比较了不同处理之间鳃大小和形状的差异。在蜻蜓可自由捕食蟌的笼子里，存活下来的北方伊氏蟌幼虫的鳃，与从蜻蜓不允许捕食蟌的处理中回收的幼虫相比，其侧表面积更大，且相对于长度更宽。这两个特征的选择差约为0.25个表型标准差单位。这些结果表明，蜻蜓捕食仍对蟌的反捕食适应施加显著的选择压力。本研究结果将在适应性研究的背景下进行讨论。
