Stickleback pelvic reduction

Reimchen hypothesized that pelvic reduction in threespine stickleback is favored by an absence of piscivorous fishes and the resulting increase in predation by insects, but Giles hypothesized that the predation regime is unimportant and that a low dissolved calcium concentration favors evolution of pelvic reduction. Substantial pelvic reduction in threespine stickleback sampled from 179 lakes around Cook Inlet, Alaska is strongly associated both with an absence of predatory fishes and a low calcium concentration. However, the association of pelvic reduction with low calcium concentration appears to be contingent on the absence of predatory fishes. These results emphasize the importance of interactions between seemingly unrelated environmental variables for selection of a single trait. However, these results also conflict with some observations elsewhere and do not rule out the possibility that other environmental factors are important for selection for pelvic reduction in threespine stickleback.

莱姆肯（Reimchen）提出假说：当湖泊中不存在食鱼鱼类（piscivorous fishes），且由此引发昆虫捕食压力升高时，三棘刺鱼（threespine stickleback）的骨盆退化（pelvic reduction）会受到正向选择；贾尔斯（Giles）则提出不同假说，认为捕食格局（predation regime）并不重要，低溶解钙浓度（dissolved calcium concentration）才会推动骨盆退化的演化。本研究对阿拉斯加库克湾周边179个湖泊采集的三棘刺鱼样本进行分析后发现，出现显著骨盆退化的个体，同时与无捕食性鱼类、低钙浓度两个因素均存在强相关性。不过，骨盆退化与低钙浓度之间的相关性似乎仅在无捕食性鱼类存在的情境下才会显现。上述研究结果凸显出，看似互不相关的环境变量之间的交互作用，在单一性状的选择过程中所发挥的关键作用。但该结果也与其他地区的部分观测结果存在冲突，且并未排除其他环境因素对三棘刺鱼骨盆退化的正向选择同样具有重要作用的可能性。