Freeman-Gallant Corey R, Taff Conor C
Department of Biology, Skidmore College, Saratoga Springs, New York, 12866, USA.
Laboratory of Ornithology, Department of Ecology & Evolutionary Biology, Cornell University, Ithaca, New York, USA.
Oecologia. 2018 Dec;188(4):1025-1036. doi: 10.1007/s00442-018-4268-2. Epub 2018 Oct 6.
Female preference for older or more disease-resistant males are both possible outcomes of parasite-mediated sexual selection, but the extent to which infection alters the development of ornaments to yield signals of male age and health has rarely been explored. In a longitudinal study of 61 male common yellowthroats (Geothlypis trichas), age-related increases in the size of the melanin-based mask and carotenoid-based bib were not correlated among young males, likely owing to differences in how blood parasites affect ornament development. Infection with trypanosomes and hemosporidians in a male's first breeding season was associated with slower growth of the mask; uninfected males attained large masks in their second breeding season, while infected males attained large masks in their third breeding season. In contrast, the bib size of males increased every year regardless of infection. As a consequence, different populations of males are identified by the largest ornaments-older males in the case of bib and a combination of older males and young, uninfected males in the case of mask. Although mask is thus the more informative trait with respect to male health, females prefer large bibs in our population. If infection is opportunistic, young, uninfected males may not possess good genes for parasite resistance but simply good luck, and it may benefit females to prefer older males who are more likely to have withstood prior episodes of selection. A "pure" signal of age may be a more reliable signal of resistance to parasites than an ornament whose expression is modulated by infection.
雌性对年龄较大或抗病能力更强的雄性的偏好，都是寄生虫介导的性选择的可能结果，但感染在多大程度上改变了雄性装饰特征的发育，从而产生雄性年龄和健康状况的信号，这一点很少有人研究。在一项对61只雄性普通黄喉地莺（Geothlypis trichas）的纵向研究中，基于黑色素的面罩和基于类胡萝卜素的喉部斑纹的大小在年轻雄性中与年龄相关的增长并无关联，这可能是由于血液寄生虫影响装饰特征发育的方式存在差异。雄性在第一个繁殖季节感染锥虫和血孢子虫与面罩生长缓慢有关；未感染的雄性在第二个繁殖季节长出大面罩，而感染的雄性在第三个繁殖季节才长出大面罩。相比之下，无论是否感染，雄性喉部斑纹的大小每年都会增加。因此，不同群体的雄性通过最大的装饰特征来区分——喉部斑纹方面是年龄较大的雄性，面罩方面是年龄较大的雄性以及年轻且未感染的雄性。尽管如此，就雄性健康而言，面罩是更具信息价值的特征，但在我们的种群中，雌性更喜欢大的喉部斑纹。如果感染是机会性的，年轻且未感染的雄性可能并不具备抗寄生虫的优良基因，而只是运气好，雌性偏好年龄较大的雄性可能更有利，因为年龄较大的雄性更有可能经受住之前的选择过程。与一个其表达受感染调节的装饰特征相比，一个“纯粹”的年龄信号可能是对寄生虫抵抗力更可靠的信号。
