Freeman-Gallant Corey R, Taff Conor C
Department of Biology, Skidmore College, Saratoga Springs, NY, 12866, USA.
Laboratory of Ornithology, Department of Ecology and Evolutionary Biology, Cornell University, Ithaca, NY, USA.
Oecologia. 2017 Aug;184(4):813-823. doi: 10.1007/s00442-017-3919-z. Epub 2017 Jul 29.
Although the selective loss of individuals susceptible to disease can favor the evolution of female preference for older males, the interrelationship between age, infection, longevity, and mating success remains poorly characterized in natural populations. In a longitudinal study of 61 male common yellowthroats (Geothlypis trichas), we found that the probability of infection with hematozoa increased as males aged from 1 to 5 years. Despite a significant, negative association between infection and longevity that partially masked age-effects, the odds that a male was infected with Trypanosoma, Plasmodium, or Leucocytozoon increased 71-212% per year. Nearly 75% of males in their first breeding season were either uninfected or infected with only a single parasite, while 50% of older males were infected with at least two parasites and 16% were infected with all three. No males escaped infection after their second breeding season. Older males were also more likely to sire extra-pair young (EPY) and, as a consequence, infection with multiple parasites was associated with a fourfold increase in the odds of producing EPY. Unlike younger males, 80% of the oldest males had a history of either surviving chronic infection or recovering. Combined with previous work showing higher diversity at the major histocompatibility complex among older males, our results suggest that the song and plumage traits that signal male age in common yellowthroats also, perforce, signal resistance to parasites. By preferring older males, females may obtain good genes for disease resistance even in the absence of any effect of infection on male ornamentation.
尽管易患疾病个体的选择性损失可能有利于雌性对年长雄性偏好的进化，但在自然种群中，年龄、感染、寿命和交配成功率之间的相互关系仍未得到充分描述。在一项对61只雄性普通黄喉地莺（Geothlypis trichas）的纵向研究中，我们发现随着雄性从1岁到5岁，感染血寄生虫的概率增加。尽管感染与寿命之间存在显著的负相关关系，部分掩盖了年龄效应，但雄性感染锥虫、疟原虫或白细胞虫的几率每年增加71%-212%。在第一个繁殖季节，近75%的雄性要么未感染，要么只感染了一种寄生虫，而50%的年长雄性至少感染了两种寄生虫，16%的雄性感染了所有三种寄生虫。没有雄性在第二个繁殖季节后逃脱感染。年长雄性也更有可能成为配偶外子代（EPY）的父亲，因此，感染多种寄生虫与产生EPY的几率增加四倍有关。与年轻雄性不同，80%最年长的雄性有过在慢性感染中存活或康复的历史。结合之前的研究表明年长雄性主要组织相容性复合体的多样性更高，我们的结果表明，在普通黄喉地莺中，表明雄性年龄的鸣声和羽毛特征也必然表明对寄生虫的抵抗力。通过偏好年长雄性，雌性即使在感染对雄性装饰没有任何影响的情况下，也可能获得抗病的优良基因。
