Data from: Genetic and environmental variation in condition, cutaneous immunity, and haematocrit in house wrens

Background: Life-history studies of wild bird populations often focus on the relationship between an individual’s condition and its capacity to mount an immune response, as measured by a commonly-employed assay of cutaneous immunity, the PHA skin test. In addition, haematocrit, the packed cell volume in relation to total blood volume, is often measured as an indicator of physiological performance. A multi-year study of a wild population of house wrens has recently revealed that those exhibiting the highest condition and strongest PHA responses as nestlings are most likely to be recruited to the breeding population and to breed through two years of age; in contrast, intermediate haematocrit values result in the highest recruitment to the population. Selection theory would predict, therefore, that most of the underlying genetic variation in these traits should be exhausted resulting in low heritability, although such traits may also exhibit low heritability because of increased residual variance. Here, we examine the genetic and environmental variation in condition, cutaneous immunity, and haematocrit using an animal model based on a pedigree of approximately 2,800 house wrens. Results: Environmental effects played a paramount role in shaping the expression of the fitness related traits measured in this wild population, but two of them, condition and haematocrit, retained significant heritable variation. Condition was also positively correlated with both the PHA response and haematocrit, but in the absence of any significant genetic correlations, it appears that this covariance arises through parallel effects of the environment acting on this
suite of traits. Conclusions: The maintenance of genetic variation in different measures of condition appears to be a pervasive feature of wild bird populations, in contradiction of conventional selection theory. A major challenge in future studies will be to explain how such variation persists in the face of the directional selection acting on condition in house wrens and other species.

背景：野生鸟类种群的生活史研究通常聚焦于个体身体状况与启动免疫应答能力之间的关联，该免疫应答能力常通过皮肤免疫的常用检测方法——PHA皮肤试验（PHA skin test）进行量化。此外，血细胞比容（haematocrit，即总血容量对应的细胞压积）常被用作生理机能的指示指标。近期一项针对家鹪鹩野生种群的多年研究显示，雏鸟阶段身体状况最优、PHA皮肤试验应答最强的个体，最有可能加入繁殖种群并可繁殖至两岁龄；与之相反，血细胞比容处于中等水平的个体种群招募率最高。因此，选择理论预测，这些性状的绝大多数潜在遗传变异应当已被耗尽，进而表现出较低的遗传力；不过这类性状的遗传力偏低也可能源于剩余方差的升高。本研究基于约2800只家鹪鹩的谱系构建动物模型，以此探究身体状况、皮肤免疫与血细胞比容的遗传与环境变异。
结果：环境效应对本次野生种群中测得的适合度相关性状的表达起到了至关重要的调控作用，但其中两项性状——身体状况与血细胞比容——仍保留了显著的可遗传变异。身体状况与PHA皮肤试验应答及血细胞比容均呈正相关，但由于未检测到显著的遗传相关，这种协变关系似乎源于环境对这一系列性状的平行作用。
结论：针对身体状况的不同量化指标，其遗传变异的维持似乎是野生鸟类种群的普遍特征，这与传统选择理论相悖。未来研究面临的一项核心挑战，便是解释在家鹪鹩与其他物种中，针对身体状况的定向选择为何仍能维持这类遗传变异。