What normal used to be: Longitudinal adrenal, reproductive, and thyroid hormone profiles from four bowhead whales during a period of Arctic stability Conservation Physiology

Assessment of large whale physiological response and resiliency to environmental change requires information about historical baseline physiological data to compare with current trends. Multi-year studies of historic and modern individual bowhead whales are possible by utilizing baleen, a keratin matrix tissue that captures a time series of physiological data across multiple years. We assessed six hormones in bowhead baleen informative of stress, reproduction, and metabolism: corticosterone, cortisol, progesterone, testosterone, triiodothyronine (T3), and dehydroepiandrosterone (and its sulfated form, collectively DHEA(S)). We also performed assay validations for DHEA(S), as this hormone has not been assessed in keratin. Through examination of longitudinal endocrine profiles of two adult males and two adult females with data from the 1940’s-1960’s, a period of relative Arctic climatic stability, we determined that reproductive cycles could be identified in adult bowhead whale baleen more than sixty years old. Testosterone cycling was observed in males while three putative pregnancies, and a fourth confirmed pregnancy, were observed in females. Strong correlations were observed between DHEA(S) and testosterone in males and pregnant females. Pregnancy displayed the strongest correlations among hormones, indicating that pregnancy is likely a form of physiological stressor that should be controlled for when studying adrenal hormones. However, in non-pregnant females, cortisol was strongly negatively correlated with progesterone and testosterone, indicating that physiological stress may influence ovarian cycling and/or likelihood of future pregnancy. Our findings underscore the importance of utilizing museum specimens to establish historical baselines, as well the value of panels of multiple hormones (representing different physiological axes) when assessing multiple stressors in free-ranging wildlife. Understanding how age, sex, and life-history stage (e.g. pregnancy) influence those hormone patterns is useful for addressing greater conservation-relevant questions, particularly related to environmental change.

评估大型鲸类对环境变化的生理响应与恢复能力，需要获取历史基准生理数据以与当前趋势开展对比。借助鲸须（baleen）——一种可记录多年生理数据时间序列的角蛋白基质组织（keratin matrix tissue）——可对历史及现代个体弓头鲸开展多年期研究。我们对弓头鲸鲸须中的6种与应激、生殖及代谢相关的激素进行了检测：皮质酮（corticosterone）、皮质醇（cortisol）、孕酮（progesterone）、睾酮（testosterone）、三碘甲状腺原氨酸（triiodothyronine, T3）以及脱氢表雄酮（dehydroepiandrosterone）及其硫酸化形式，统称为DHEA(S)。由于此前尚未在角蛋白组织中对该激素开展过检测，我们还针对DHEA(S)完成了检测方法验证。通过分析2头成年雄性与2头成年雌性弓头鲸的纵向内分泌特征谱（数据来自北极气候相对稳定的1940年代至1960年代），我们发现，可在超过60年历史的成年弓头鲸鲸须中识别出生殖周期。雄性个体中可观察到睾酮的周期波动，雌性个体中则发现了3次推定妊娠与1次确诊妊娠。雄性与妊娠雌性个体中，DHEA(S)与睾酮均呈现显著相关性。妊娠与各类激素间的相关性最为显著，这表明妊娠可能属于一种生理应激源，在研究肾上腺激素时需对其加以控制。但在非妊娠雌性个体中，皮质醇与孕酮、睾酮均呈显著负相关，这提示生理应激可能会影响卵巢周期或未来妊娠概率。本研究结果凸显了利用馆藏标本建立历史基准的重要性，以及在评估野外自由活动的野生动物的多重应激源时，采用覆盖不同生理轴的多激素组合检测的价值。明确年龄、性别与生活史阶段（如妊娠）如何影响激素模式，有助于解答更多与保护相关的核心问题，尤其是与环境变化相关的保护议题。