School of Biological Sciences, University of Auckland, Auckland, New Zealand.
J R Soc Interface. 2011 Nov 7;8(64):1654-64. doi: 10.1098/rsif.2011.0207. Epub 2011 May 11.
Obligate brood parasitic birds lay their eggs in nests of other species and parasite eggs typically have evolved greater structural strength relative to host eggs. Increased mechanical strength of the parasite eggshell is an adaptation that can interfere with puncture ejection behaviours of discriminating hosts. We investigated whether hardness of eggshells is related to differences between physical and chemical traits from three different races of the parasitic common cuckoo Cuculus canorus, and their respective hosts. Using tools developed for materials science, we discovered a novel correlate of increased strength of parasite eggs: the common cuckoo's egg exhibits a greater microhardness, especially in the inner region of the shell matrix, relative to its host and sympatric non-host species. We then tested predictions of four potential mechanisms of shell strength: (i) increased relative thickness overall, (ii) greater proportion of the structurally harder shell layers, (iii) higher concentration of inorganic components in the shell matrix, and (iv) elevated deposition of a high density compound, MgCO(3), in the shell matrix. We confirmed support only for hypothesis (i). Eggshell characteristics did not differ between parasite eggs sampled from different host nests in distant geographical sites, suggesting an evolutionarily shared microstructural mechanism of stronger parasite eggshells across diverse host-races of brood parasitic cuckoos.
专性巢寄生鸟类将其卵产在其他物种的巢中，寄生卵通常比宿主卵具有更大的结构强度。寄生虫卵壳的机械强度增加是一种适应，可以干扰有辨别能力的宿主的刺穿和弹射行为。我们研究了寄生性普通杜鹃 Cuculus canorus 的三个不同亚种与其各自宿主之间，卵壳硬度是否与物理和化学特征的差异有关。我们使用为材料科学开发的工具，发现了寄生虫卵强度增加的一个新的相关因素：与宿主和同域非宿主物种相比，普通杜鹃的卵具有更大的微观硬度，尤其是在壳基质的内部区域。然后，我们测试了四种潜在的壳强度机制的预测：（i）整体上相对厚度增加，（ii）结构更硬的壳层比例增加，（iii）壳基质中无机成分浓度增加，以及（iv）壳基质中高密度化合物 MgCO3 的沉积增加。我们仅证实了假设（i）的支持。在不同地理位置的不同宿主巢中采集的寄生卵的卵壳特征没有差异，这表明在不同宿主种系的杜鹃寄生鸟类中，寄生虫卵壳的更强微观结构机制是进化共享的。
