Brood-parasitic cuckoos lay their eggs in the nests of other birds and thereafter abandon their young to the care of the host. Thus, all maternal investment is restricted to investment in the egg. Optimal investment at this stage is likely to have a large impact on maternal reproductive success. Many bird species optimize the size of their eggs to suit both the prevailing environmental conditions and the number of individuals that will provide care to the chicks. However, relatively few cues are available to avian brood parasites to facilitate optimal investment in their eggs. Moreover, optimization of egg size to suit environmental conditions or the social structure of the host group may be constrained by stronger selection for egg mimicry, which reduces the likelihood of detection and rejection of foreign eggs by the host. We aimed to test how the conflicting selection pressures of (1) selection for large eggs in harsh environmental conditions versus (2) rejection of large eggs by hosts interact to influence the size and shape of Horsfield's bronze-cuckoo, Chalcites basalis, eggs. Using a sliding window approach to investigate periods of climate sensitivity, we show that climatic variables did not predict egg size. Nor did cuckoos modify their egg size or shape in relation to the group size of the host (superb fairy-wren, Malurus cyaneus). Conversely, host defences did appear to have influenced cuckoo egg morphology: eggs that were relatively short and round had a higher probability of being abandoned by the host than eggs that were long and narrow. This suggests that host defences are the overriding selection pressure on cuckoo egg morphology, and, unlike their hosts, cuckoos do not adapt their eggs to the prevailing climate or host group size.

中文翻译：

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育雏寄生杜鹃如何调和环境和宿主选择对鸡蛋大小投资的压力？

寄生寄生的杜鹃在其他鸟类的巢穴中产卵，然后将幼鸟交给寄主照顾。因此，所有母体投资都仅限于对卵子的投资。这个阶段的最佳投资很可能对母体的生殖成功产生很大影响。许多鸟类都会优化其蛋的大小，以适应普遍的环境条件和照顾雏鸡的个体数量。然而，可用于鸟类繁殖寄生虫以促进对其卵的最佳投资的线索相对较少。此外，为了适应环境条件或宿主群体的社会结构而优化鸡蛋大小可能会受到对鸡蛋拟态的更强选择的限制，这降低了宿主检测和排斥外来鸡蛋的可能性。我们的目的是测试 (1) 在恶劣环境条件下选择大卵与 (2) 宿主拒绝大卵的冲突选择压力如何相互作用以影响霍斯菲尔德青铜杜鹃、 Chalcites basalis 卵的大小和形状。使用滑动窗口方法来研究气候敏感期，我们表明气候变量并不能预测鸡蛋的大小。杜鹃也没有根据宿主的群体大小改变它们的蛋大小或形状（极好的仙女鹪鹩，Malurus cyaneus）。相反，宿主防御似乎确实影响了布谷鸟卵的形态：相对短而圆的卵比长而窄的卵更容易被宿主遗弃。这表明宿主防御是杜鹃卵形态上压倒一切的选择压力，并且，