Lyon Bruce E
Department of Ecology and Evolutionary Biology, University of California, Santa Cruz, California 95064, USA.
Nature. 2003 Apr 3;422(6931):495-9. doi: 10.1038/nature01505.
Birds parasitized by interspecific brood parasites often adopt defences based on egg recognition but such behaviours are puzzlingly rare in species parasitized by members of the same species. Here I show that conspecific egg recognition is frequent, accurate and used in three defences that reduce the high costs of conspecific brood parasitism in American coots. Hosts recognized and rejected many parasitic eggs, reducing the fitness costs of parasitism by half. Recognition without rejection also occurred and some hosts banished parasitic eggs to inferior outer incubation positions. Clutch size comparisons revealed that females combine egg recognition and counting to make clutch size decisions--by counting their own eggs, while ignoring distinctive parasitic eggs, females avoid a maladaptive clutch size reduction. This is clear evidence that female birds use visual rather than tactile cues to regulate their clutch sizes, and provides a rare example of the ecological and evolutionary context of counting in animals.
被种间巢寄生鸟类寄生的宿主通常会采取基于识别鸟蛋的防御措施，但令人费解的是，在被同物种成员寄生的物种中，这种行为却极为罕见。在此我表明，在美国黑鸭中，同种鸟蛋识别行为很常见且准确，并被用于三种防御机制中，这些机制可降低同种巢寄生带来的高昂代价。宿主能够识别并拒绝许多寄生鸟蛋，将寄生造成的适合度成本降低了一半。也会出现识别但不拒绝的情况，一些宿主会将寄生鸟蛋移至较差的外层孵化位置。窝卵数比较表明，雌性黑鸭会结合鸟蛋识别和计数来决定窝卵数——通过数自己的蛋，同时忽略独特的寄生鸟蛋，雌性黑鸭避免了不适应的窝卵数减少。这清楚地证明了雌鸟利用视觉而非触觉线索来调节窝卵数，并且提供了一个动物计数的生态和进化背景的罕见例子。
