Data from: Hosts of avian brood parasites have evolved egg signatures with elevated information content

Hosts of brood-parasitic birds must distinguish their own eggs from parasitic mimics, or pay the cost of mistakenly raising a foreign chick. Egg discrimination is easier when different host females of the same species each lay visually distinctive eggs (egg ‘signatures’), which helps to foil mimicry by parasites. Here, we ask whether brood parasitism is associated with lower levels of correlation between different egg traits in hosts, making individual host signatures more distinctive and informative. We used entropy as an index of the potential information content encoded by nine aspects of colour, pattern and luminance of eggs of different species in two African bird families (Cisticolidae parasitized by cuckoo finches Anomalospiza imberbis, and Ploceidae by diederik cuckoos Chrysococcyx caprius). Parasitized species showed consistently higher entropy in egg traits than did related, unparasitized species. Decomposing entropy into two variation components revealed that this was mainly driven by parasitized species having lower levels of correlation between different egg traits, rather than higher overall levels of variation in each individual egg trait. This suggests that irrespective of the constraints that might operate on individual egg traits, hosts can further improve their defensive ‘signatures' by arranging suites of egg traits into unpredictable combinations.

巢寄生鸟类的宿主必须区分自身所产的卵与寄生性拟态卵，否则将承担误养外来雏鸟的代价。当同一物种的不同宿主雌性个体各自产下视觉特征独特的卵（卵‘签名’）时，卵识别任务会更容易完成，这有助于抵御寄生虫的拟态攻击。本研究旨在探究巢寄生是否与宿主不同卵性状间的相关性降低相关，从而使单个宿主的卵签名更具独特性与信息价值。我们以信息熵（entropy）作为潜在信息含量的量化指标，分析了两个非洲鸟类类群的不同物种卵的9项颜色、图案与亮度特征：其中扇尾莺科（Cisticolidae）受杜鹃雀（Anomalospiza imberbis）寄生，织布鸟科（Ploceidae）受狄氏金鹃（Chrysococcyx caprius）寄生。被寄生的物种在卵性状上展现出始终更高的信息熵值。将熵分解为两个变异组分后发现，这一现象主要源于被寄生物种的不同卵性状间相关性更低，而非单个卵性状的整体变异水平更高。这表明，无论单个卵性状受到何种演化约束，宿主均可通过将整套卵性状组合为不可预测的模式，进一步优化其防御性‘签名’。