Table_1_Good times bad times — Unfavorable breeding conditions, more than divorce, lead to increased parental effort and reduced physiological condition of northern gannets.docx

Decreased productivity in long-lived bird species is linked to prey depletion in marine ecosystems. Seabirds, however, exhibit behavioral flexibility at individual level to prevent this outcome. One such strategy to alleviate any impact on fitness would be to divorce from their partners. Although changing mates and increasing foraging effort have been shown to increase or maintain reproductive success, how the behavioral flexibility affects fundamental physiological parameters remains to be elucidated. Here, we compared physiological components (nutritional status, muscle damage and oxidative stress) of northern gannets (Morus bassanus) in relation to their partnership status and foraging effort. Specifically, we used a cross-sectional data set (at the population level) of three contrasted years to compare retained and changed mates. We predicted that mate change is a stressful event with impacts on health condition and those effects are higher during unfavorable years with food depletion. Our study showed that gannets changing mate increase parental effort only during years of low food abundance, with consequences on health condition (increased body mass loss, higher protein catabolism and higher oxidative damage during chick rearing period). Ultimately, our study suggests that partnership decision is not likely to reduce the long-term quality and the fitness of parents. Reproduction during harsh conditions would however likely be one of the primary causes of individual quality loss and fitness decline in this long-lived bird species.

长寿鸟类种群的繁殖力下降与海洋生态系统中的猎物枯竭密切相关。然而海鸟个体层面展现出行为可塑性，以规避此类结果。其中一种缓解适合度（fitness）受损风险的策略，便是与配偶离异。尽管已有研究证实，更换配偶与增加觅食投入可提升或维持繁殖成功率，但这种行为可塑性如何影响核心生理参数仍有待阐明。在此，我们针对北方塘鹅（学名：Morus bassanus）的生理指标（营养状态、肌肉损伤与氧化应激水平）与配偶状态及觅食投入的关联展开比较分析。具体而言，我们借助三年环境迥异的种群水平横断面数据集，对比了维持原有配偶与更换配偶的个体。我们提出假设：更换配偶属于应激事件，会对健康状态产生负面影响，且在食物枯竭的恶劣年份，此类影响会更为显著。本研究发现，仅在食物资源匮乏的年份，更换配偶的塘鹅才会提升双亲投入，同时其健康状态会受到损伤：育雏期体重流失加剧、蛋白质分解代谢增强、氧化损伤程度升高。综上，本研究表明，配偶选择决策并不会降低亲本的长期质量与适合度。不过，在恶劣环境条件下进行繁殖，仍可能是该长寿鸟类种群个体质量下降与适合度降低的主要诱因之一。