Experience and trust: The benefits of mate familiarity are realized through sex-specific specialization of parental roles in cassin’s auklet

Maintaining a pair bond year after year (perennial monogamy) often enhances reproductive success, but what familiar pairs are doing differently to improve success is unknown. We tested the hypothesis that endocrine changes mediate improvements in parental attendance in known-age Cassin’s auklets Ptychoramphus aleuticus, which we found limited evidence for. Instead, we found sex-specific parental roles in familiar pairs. Males modulated their nest attendance depending on the attendance of their mate, but the direction depended on mate familiarity.  We suggest his flexibility may be mediated by prolactin. In a historical dataset, females with a familiar mate laid larger eggs that hatched into more robust chicks, but larger eggs correlated with lower female body condition. In study birds, attendance by males and females in good condition predicted chick weight, but attendance by females in poor condition did not, suggesting female-specific energetic constraint. Our findings suggest that ma..., Fieldwork and sample collection: We conducted our study on Southeast Farallon Island (37.6989° N, 123.0034° W; Farallon Islands National Wildlife Refuge, California, USA) in 2019 and 2021. These two years represented a positive El Niño Southern Oscillation (ENSO) event where on average only 8% of followed pairs fledged a chick (2019), and a negative ENSO event (2021) where 65% of pairs fledged a chick [1]. Many individuals of the Southeast Farallon Island Cassin’s auklet population are of known age and have known reproductive histories [2], allowing us to disentangle the confounding effects of age and mate familiarity. Nest boxes were checked every 15 days until an incubating bird was found. If the individual was of known age, it was measured and evaluated for inclusion in the study. All morphometrics are therefore from birds in their first two weeks of incubation. We weighed known-age incubating adults between 13:00 and 15:00 with a Pesola spring scale (+/- 1g), measured wing cord with..., , # Experience and trust: The benefits of mate familiarity are realized through sex-specific specialization of parental roles in cassin’s auklet [https://doi.org/10.5061/dryad.mcvdnck82](https://doi.org/10.5061/dryad.mcvdnck82) The data presented here are endocrine, behavior, and fitness metrics from Cassin's auklets collected in 2019 and 2021 on Southeast Farallon Island, California. Endocrine measurements are levels of fecal corticosterone and plasma prolactin. Behavioral measurements were the proportion of nights an individual was present at the nest during both incubation and chick rearing. Fitness metrics include hatching and fledging success, and the maximum weight the chick attained. There is also some basic information about each bird in the dataset, such as its age if known, sex, and body condition. It also includes information on egg volumes from individuals where egg morphometrics were taken between 1992 and 2017, and information about the females that laid those eggs. ## De...### 研究背景与核心发现 维持多年配偶绑定（终身单配制，perennial monogamy）通常可提升繁殖成功率，但熟悉的配偶对究竟通过何种差异化策略提升繁殖成功率仍不明晰。本研究针对已知年龄的卡氏海雀（Cassin’s auklet，*Ptychoramphus aleuticus*），检验了「内分泌变化介导亲鸟育雏出勤改善」这一假说，但仅获得有限支持。与之相反，我们发现熟悉配偶对中存在性别特异性的亲鸟角色分工：雄鸟会根据配偶的出勤情况调整自身巢箱出勤行为，但其调整方向取决于配偶间的熟悉程度。我们推测该行为可塑性可能由催乳素（prolactin）介导。在历史数据集内，拥有熟悉配偶的雌鸟会产下更大的卵，其孵化出的雏鸟也更强健，但较大的卵与雌鸟较差的身体状况呈相关性。在本研究的观测个体中，身体状况良好的雌雄亲鸟的出勤行为可预测雏鸟体重，但身体状况较差的雌鸟出勤行为则无此关联，这提示雌鸟存在特异性的能量约束。我们的研究结果表明…… ## 野外工作与样本采集 本研究于2019年和2021年在美国加利福尼亚州法拉隆群岛国家野生动物保护区的东南法拉隆岛（37.6989° N，123.0034° W）开展。这两年分别对应正相位厄尔尼诺南方涛动（ENSO）事件：2019年为正相位ENSO年，当年跟踪的繁殖对平均仅8%成功育雏；2021年为负相位ENSO年，当年65%的繁殖对成功育雏[1]。东南法拉隆岛的卡氏海雀种群中，多数个体年龄已知且具有可追溯的繁殖历史[2]，这使得我们能够厘清年龄与配偶熟悉度之间的混淆效应。研究人员每15天检查一次巢箱，直至发现正在孵卵的个体。若该个体年龄已知，则对其进行形态学测量并评估是否纳入本研究，因此所有形态学测量数据均采集自孵卵初期两周内的个体。我们于13:00至15:00间使用Pesola弹簧秤（精度±1g）对已知年龄的孵卵成鸟称重，测量翅长时…… # 经验与信任：配偶熟悉度的收益通过卡氏海雀亲鸟角色的性别特异性特化实现 本数据集收录了2019年与2021年在加利福尼亚州东南法拉隆岛采集的卡氏海雀的内分泌、行为与适合度指标。其中内分泌测量指标为粪便皮质酮与血浆催乳素水平；行为测量指标为个体在孵卵与育雏期内夜间出勤巢箱的比例；适合度指标包括孵化成功率、育雏成功率以及雏鸟的最大体重。数据集同时包含每只个体的基础信息，如已知年龄、性别与身体状况。此外还收录了1992年至2017年间测量过卵形态学指标的个体的卵体积数据，以及产下这些卵的雌鸟的相关信息。 数据集DOI：https://doi.org/10.5061/dryad.mcvdnck82