Data from: Body reserves influence allocation to immune responses in capital breeding female northern elephant seals

Mounting an immune response requires substantial energy. Ecological immunology theory predicts allocation trade-offs between reproductive effort and immune responses under conditions of energy limitation. Little is known about the impact of capital breeding strategies on energy allocation to immune function in mammals. Northern elephant seals (NES) forage in the marine environment, breed in dense terrestrial colonies and exhibit high rates of energy expenditure for lactation while fasting. Body reserves strongly influence reproductive effort and lactation requires elevation of plasma cortisol for energy mobilization. We characterized immune response by measuring a suite of immune markers including cytokines, an acute phase protein, and immunoglobulins early and late in breeding and moult haul-outs in 197 samples from 129 female NES. We explored potential impacts of breeding, body condition and plasma cortisol on immune function. Immune responses were greater and more varied during breeding. Adiposity had positive associations with innate immune responses across all life-history stages. Body mass had positive associations with both adaptive and innate immune responses early in fasts. Females with lower fat reserves showed reduced innate immune responses at the end of lactation. Immunoglobulin E, a marker of immune response to parasitic infection, exhibited a significant negative association with cortisol across all life-history stages. These data suggest that breeding carries an immune cost and provide evidence for allocation trade-offs between immune function and breeding effort. These trade-offs may reflect a compromise between immune costs inherent in colonial breeding and energetic limitations that arise in use of capital breeding strategies. Variation in evidence for immunosuppressive effects of cortisol suggests that decoupling of these effects may be limited to specific aspects of the immune response during terrestrial fasting. Immune responses that are required for survival may be modulated relative to the energetic demands required for successful reproduction.

启动免疫应答需要消耗大量能量。生态免疫学（ecological immunology）理论预测，在能量受限的条件下，生物会在繁殖投入与免疫应答之间存在资源分配权衡。目前学界对资本繁殖策略（capital breeding strategy）对哺乳动物免疫功能能量分配的影响知之甚少。北象海豹（Northern Elephant Seals, NES）在海洋环境中觅食，于密集的陆地聚居地繁殖，并在禁食哺乳期间消耗极高的能量。身体储备显著影响繁殖投入，而哺乳过程需要升高血浆皮质醇（cortisol）水平以动员能量。我们通过采集129头雌性北象海豹的197份样本，检测其中繁殖期与换毛期上岸早期和晚期的一系列免疫标志物——包括细胞因子（cytokine）、一种急性期蛋白（acute phase protein）以及免疫球蛋白E（Immunoglobulin E）——以表征免疫应答。我们探究了繁殖状态、身体状况以及血浆皮质醇水平对免疫功能的潜在影响。繁殖期的免疫应答更强且更具多样性。在所有生命史阶段，体脂量与先天免疫应答（innate immune response）均呈正相关。禁食早期的体质量与适应性及先天免疫应答均呈正相关。体内脂肪储备较低的雌性个体在哺乳末期的先天免疫应答会减弱。作为寄生虫感染免疫应答标志物的免疫球蛋白E，在所有生命史阶段均与皮质醇水平呈显著负相关。本研究数据表明，繁殖过程存在免疫成本，并为免疫功能与繁殖投入之间的资源分配权衡提供了证据。这类权衡可能反映了聚居繁殖固有的免疫成本与采用资本繁殖策略所产生的能量限制之间的折中。皮质醇免疫抑制效应的相关证据存在差异，这表明这类效应的解耦可能仅局限于陆地禁食期间免疫应答的特定方面。为生存所必需的免疫应答，可能会根据成功繁殖所需的能量需求进行调控。