Abstract

Migratory shorebirds (Charadrii) show a strong dichotomy in their breeding and wintering strategies: Arctic-breeding species typically spend the wintering season in marine habitats, while more southerly breeding species tend to do so in freshwater habitats where pathogens and parasites, particularly vector-borne blood parasites, are generally more abundant. Thus, it has been hypothesized that the former group may reduce their investment in immunity, but experimental data supporting this hypothesis are lacking. Moreover, whether this contrasting habitat selection can shape investments in immunocompetence among populations within a species is uncertain. We experimentally tested the hypothesis that there is a significant association between habitat occupancy and the strength of a pro-inflammatory immune response in the Dunlin (Calidris alpina), a widely distributed long-distance migratory shorebird that breeds in (sub-)arctic areas and winters mainly, but not exclusively, in coastal habitats. Overwintering Dunlins occupying inland freshwater and marine habitats at a similar latitude were captured and acclimated under identical conditions in outdoor aviaries. After an acclimation period, they were challenged with phytohemagglutinin to assess the pro-inflammatory immune response and its associated energetic costs, measured by basal metabolic rate (BMR) and body mass changes. We found that freshwater Dunlins exhibited a higher (63%) pro-inflammatory immune response than marine Dunlins. Although this difference did not involve significant BMR changes, the time course of body mass response differed between freshwater and marine individuals. Our findings point to the existence of different pro-inflammatory immune responses and body mass adjustments associated with the wintering habitat. These intraspecific differences are likely due to population adaptation rather than phenotypic plasticity, where not only disease risk but also physiological adaptations to different salinity levels could play an important role.

中文翻译：

---

促炎性免疫反应与迁徙水鸟越冬栖息地有关

摘要

候鸟（Charadrii）在繁殖和越冬策略上表现出强烈的二分法：北极繁殖物种通常在海洋栖息地度过越冬季节，而更南端的繁殖物种则倾向于在病原体和寄生虫（尤其是媒介传播）的淡水栖息地度过血液中的寄生虫，一般都比较丰富。因此，据推测，前者可能会减少他们对免疫力的投资，但是缺乏支持该假设的实验数据。此外，这种不同的栖息地选择是否能够影响物种内种群之间免疫能力的投资尚不确定。我们通过实验检验了以下假设，即在Dunlin中，栖息地占用与促炎免疫反应强度之间存在显着关联（Calidris alpina），一种广泛分布的长途迁徙水鸟，主要在（亚）北极地区和冬季繁殖，但不仅仅在沿海栖息地繁殖。在相同的条件下，在相同的纬度下捕获并适应了内陆淡水和海洋栖息地的越冬Dunlins，并使其适应了室外鸟舍。适应期过后，他们接受植物血凝素挑战，以评估促炎性免疫反应及其相关的能量消耗，以基础代谢率（BMR）和体重变化来衡量。我们发现淡水的Dunlins比海洋Dunlins表现出更高的（63％）促炎免疫反应。尽管这种差异并不涉及BMR的显着变化，但淡水和海洋个体的体重反应时间却有所不同。我们的发现指出存在与越冬栖息地相关的不同的促炎性免疫反应和体重调节。这些种内差异可能是由于种群适应而不是表型可塑性引起的，其中不仅疾病风险而且生理适应不同盐度水平也可能起重要作用。