Data from: Baseline immune activity is associated with date rather than with moult stage in the Arctic-breeding barnacle goose (Branta leucopsis)

Variation in immune defence in birds is often explained either by external factors such as food availability and disease pressure or by internal factors such as moult and reproductive effort. We explored these factors together in one sampling design by measuring immune activity over the time frame of the moulting period of Arctic-breeding barnacle geese (Branta leucopsis). We assessed baseline innate immunity by measuring levels of complement-mediated lysis and natural antibody-mediated agglutination together with total and differential leukocyte counts. Variation in immune activity during moult was strongly associated with calendar date and to a smaller degree with the growth stage of wing feathers. We suggest that the association with calendar date reflected temporal changes in the external environment. This environmental factor was further explored by comparing the immune activity of geese in the Arctic population with conspecifics in the temperate climate zone at comparable moult stages. In the Arctic environment, which has a lower expected disease load, geese exhibited significantly lower values of complement-mediated lysis, their blood contained fewer leukocytes, and levels of phagocytic cells and reactive leukocytes were relatively low. This suggests that lower baseline immune activity could be associated with lower disease pressure. We conclude that in our study species, external factors such as food availability and disease pressure have a greater effect on temporal variation of baseline immune activity than internal factors such as moult stage.鸟类免疫防御的变异通常可通过两类因素解释：一类为食物可获得性、疾病压力等外部因素，另一类为换羽、繁殖投入等内部因素。本研究采用统一采样设计，对北极繁殖的白额黑雁（Branta leucopsis）换羽期的免疫活性进行测定，以联合探究上述两类因素的影响。我们通过检测补体介导的裂解、天然抗体介导的凝集水平，以及白细胞总数与分类计数，评估了其基础先天免疫功能。研究发现，换羽期的免疫活性变异与日历日期显著相关，仅在较小程度上与翼羽生长阶段相关。我们推测，与日历日期的关联反映了外部环境的时序变化。为进一步探究该环境因素，我们将北极种群的白额黑雁与处于相似换羽阶段的温带气候区同种个体的免疫活性进行了对比。在预期疾病负荷更低的北极环境中，白额黑雁的补体介导裂解活性显著更低，血液中白细胞数量更少，吞噬细胞与反应性白细胞水平也相对较低。这表明较低的基础免疫活性可能与更低的疾病压力相关。综上，在本研究的物种中，食物可获得性、疾病压力等外部因素对基础免疫活性时序变异的影响，要大于换羽阶段等内部因素。