Natural selection should favour strategies that maximise reproductive success. Females may use different resources during progressive stages of reproduction according to energetic demands, behavioural constraints and prey availability. We used South American fur seal, Arctocephalus australis australis, pup whisker isotope values as proxies for maternal diet and habitat use to determine how resource use (1) changes throughout pup development from in utero growth to mid-end of lactation and (2) how it differs among individuals. The longest whisker was cut from 5 male and 5 female fur seal pups (of approximately 8 months of age) at Bird Island, Falkland Islands, in 2018, and δ15N values and δ13C values were analysed every 5 mm along the length of each whisker. Patterns in δ13C values indicated that mothers used different habitats during the annual cycle, likely coinciding with seasonal shifts in prey availability or distribution. The individual specialisation index based on δ13C values was 0.34, indicating that adult females used different habitats, which could reduce intra-specific competition and ultimately enhance pup growth and survival. An increase in δ15N values occurred along every pup whisker from pup birth to mid-end of lactation, which likely reflected trophic enrichment related to suckling and fasting by pups, overriding the maternal isotopic signature. Pup whisker stable isotopes are useful proxies of maternal foraging ecology. However, physiological processes complicate interpretations by altering δ15N values. Interpreting these values therefore requires additional knowledge of the species’ ecology and physiology.

中文翻译：

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南美海狗幼崽胡须的稳定同位素值作为全年母体觅食生态的代表

自然选择应该支持最大化繁殖成功的策略。根据能量需求、行为限制和猎物的可用性，雌性在繁殖的渐进阶段可能会使用不同的资源。我们使用南美海狗 Arctocephalus australis australis、幼崽须同位素值作为母体饮食和栖息地使用的代理，以确定资源使用 (1) 从子宫内生长到哺乳中期的幼崽发育过程中如何变化和 (2)它因人而异。最长的胡须是 2018 年在福克兰群岛伯德岛从 5 只雄性和 5 只雌性海狗幼崽（大约 8 个月大）中切下的，沿着每条胡须的长度每 5 毫米分析 δ15N 值和 δ13C 值。δ13​​C 值的模式表明母亲在年度周期中使用不同的栖息地，这可能与猎物可用性或分布的季节性变化相吻合。基于δ13C值的个体特化指数为0.34，表明成年雌性利用不同的栖息地，可以减少种内竞争，最终促进幼崽的生长和存活。从幼崽出生到泌乳中期，δ15N 值沿着每只幼崽的胡须发生增加，这可能反映了与幼崽哺乳和禁食相关的营养丰富，凌驾于母体同位素特征之上。幼崽须稳定同位素是母体觅食生态的有用代表。然而，生理过程通过改变 δ15N 值使解释复杂化。