Socioecological predictors of immune defenses in wild spotted hyenas

Social rank can profoundly affect many aspects of mammalian reproduction and stress physiology, but little is known about how immune function is affected by rank and other socioecological factors in free-living animals.

In this study, we examine the effects of sex, social rank and reproductive status on immune function in long-lived carnivores that are routinely exposed to a plethora of pathogens, yet rarely show signs of disease.

Here, we show that two types of immune defences, complement-mediated bacterial killing capacity (BKC) and total IgM, are positively correlated with social rank in wild hyenas, but that a third type, total IgG, does not vary with rank.

Female spotted hyenas, which are socially dominant to males in this species, have higher BKC, and higher IgG and IgM concentrations, than do males.

Immune defences are lower in lactating than pregnant females, suggesting the immune defences may be energetically costly.

Serum cortisol and testosterone concentrations are not reliable predictors of basic immune defences in wild female spotted hyenas.

These results suggest that immune defences are costly and multiple socioecological variables are important determinants of basic immune defences among wild hyenas. The effects of these variables should be accounted for when attempting to understand disease ecology and immune function.

社会等级（social rank）可深刻影响哺乳动物繁殖与应激生理学的诸多方面，但目前对于自由生活野生动物的免疫功能如何受社会等级及其他社会生态因素影响，仍知之甚少。
本研究针对一类寿命较长的食肉目动物展开，这类动物长期频繁暴露于大量病原体之中却极少表现出疾病症状，借此探究性别、社会等级与繁殖状态对其免疫功能的调控效应。
研究结果显示，在野生斑鬣狗中，两类免疫防御指标——补体介导的杀菌能力（complement-mediated bacterial killing capacity, BKC）与总IgM——的水平与社会等级呈显著正相关，而第三类指标总IgG的水平则未随等级发生变化。
该物种中雌性斑鬣狗的社会等级高于雄性，其BKC水平以及IgG、IgM的浓度均显著高于雄性个体。
哺乳期雌性的免疫防御水平低于妊娠雌性，这提示免疫防御存在能量成本。
血清皮质醇与睾酮浓度无法有效预测野生雌性斑鬣狗的基础免疫防御水平。
上述结果表明，免疫防御存在能量成本，且多项社会生态变量是野生斑鬣狗基础免疫防御水平的重要决定因素。在探究疾病生态学与免疫功能的研究中，应充分考量这些变量的影响效应。