Koufopanou Vasso, Bell Graham
Biology Department, McGill University, 1205 Ave Dr. Penfield, H3A 1B1, Montreal, Quebec, Canada.
Oecologia. 1984 Sep;64(1):81-86. doi: 10.1007/BF00377548.
Gravid and barren Daphnia pulex were exposed to a variety of predators in laboratory aquaria. Small fish (guppies, sticklebacks and shiner fry) consistently preferred the gravid females, establishing the existence of a behavioural cost of reproduction. However, no such cost was associated with predation by more efficient visual predators (sunfish) or by nonvisual predators (hydras), and the excess of gravid females eaten by backswimmers was found to be attributable to their distribution in the water column. Moreover, the cost associated with predation by small fish was observed only when the Daphnia were presented against a light background, and was abolished when a dark background was substituted. In a further series of experiments with guppies we attempted to show that each egg added to the brood caused a decrease in survival; in two such experiments survival rate was related to body size but not to fecundity, while in a third the effect of body size did not appear, and a negative correlation between survival and fecundity could be demonstrated. Although these experiments unambiguously demonstrate a cost of reproduction they also illustrate the elusiveness of the phenomenom and emphasize the need to develop theories which specify the type and magnitude of costs generated by different ways of life.
将怀孕和未怀孕的水蚤暴露在实验室水族箱中的各种捕食者面前。小型鱼类（孔雀鱼、棘鱼和银汉鱼幼鱼）一直更喜欢怀孕的雌性水蚤，这证实了繁殖存在行为成本。然而，更高效的视觉捕食者（太阳鱼）或非视觉捕食者（水螅）的捕食并没有带来这样的成本，而且发现仰泳蝽吃掉的怀孕雌性水蚤过多是由于它们在水柱中的分布情况。此外，只有当水蚤在浅色背景下出现时，才观察到小型鱼类捕食带来的成本，而换成深色背景时，这种成本就消失了。在另一系列用孔雀鱼进行的实验中，我们试图证明每增加一枚卵到卵群中都会导致存活率下降；在其中两个这样的实验中，存活率与体型有关，而与繁殖力无关，而在第三个实验中，体型的影响并未出现，但可以证明存活率与繁殖力之间存在负相关。尽管这些实验明确证明了繁殖成本的存在，但它们也说明了这种现象难以捉摸，并强调需要发展理论来明确不同生活方式产生的成本类型和大小。
