1 School of Biological Sciences, Royal Holloway University of London , Egham, Surrey TW20 0EX , UK.
2 Department of Zoology, University of Cambridge , Downing Street, Cambridge CB2 3EJ , UK.
Philos Trans R Soc Lond B Biol Sci. 2019 Apr 1;374(1769):20180194. doi: 10.1098/rstb.2018.0194.
Brood parasitism has evolved independently in several bird lineages, giving rise to strikingly similar behavioural adaptations that suggest convergent evolution. By comparison, convergence of physiological traits that optimize this breeding strategy has received much less attention, yet these species share many similar physiological traits that optimize this breeding strategy. Eggshell structure is important for embryonic development as it controls the flux of metabolic gases, such as O, CO and HO, into and out of the egg; in particular, water vapour conductance ( G) is an essential process for optimal development of the embryo. Previous work has shown that common cuckoos ( Cuculus canorus) have a lower than expected eggshell G compared with their hosts. Here, we sought to test whether this is a trait found in other independently evolved avian brood parasites, and therefore reflects a general adaptation to a parasitic lifestyle. We analysed G for seven species of brood parasites from four unique lineages as well as for their hosts, and combined this with species from the literature. We found lower than expected G among all our observed brood parasites both compared with hosts (except for brown-headed cowbirds ( Molothrus ater)) and compared with the expected rates given their phylogenetic positions. These findings suggest that a lowered G may be a general adaptation for brood parasitism, perhaps helping the parasite nestling to develop greater aerobic fitness. This article is part of the theme issue 'The coevolutionary biology of brood parasitism: from mechanism to pattern'.
巢寄生在几个鸟类谱系中独立进化，产生了惊人相似的行为适应性，表明存在趋同进化。相比之下，这种繁殖策略的生理特征的趋同优化受到的关注要少得多，但这些物种确实有许多相似的生理特征，这些特征优化了这种繁殖策略。蛋壳结构对于胚胎发育很重要，因为它控制着代谢气体（如 O、CO 和 HO）进出卵子的通量；特别是，水蒸气传导率（G）是胚胎最佳发育的一个必要过程。之前的工作表明，普通杜鹃（ Cuculus canorus）的蛋壳 G 低于与其宿主的预期值。在这里，我们试图测试这是否是在其他独立进化的鸟类巢寄生者中发现的特征，因此反映了对寄生生活方式的普遍适应。我们分析了来自四个独特谱系的七种巢寄生者及其宿主的 G，并将其与文献中的物种结合起来进行分析。我们发现，在所观察到的所有巢寄生者中，其 G 都低于宿主（除了棕色头牛鹂（ Molothrus ater）），并且与其系统发育位置的预期值相比也较低。这些发现表明，降低 G 可能是巢寄生的一种普遍适应，这可能有助于寄生虫雏鸟发展更大的有氧适应能力。本文是主题为“巢寄生的协同进化生物学：从机制到模式”的特刊的一部分。
