Age at maturity is an important parameter in many demographic models and, for some species, can be difficult to obtain using traditional methods. Incremental growth structures act as biological archives, recording information throughout an organism's life and possibly allowing for the reconstruction of life history events. Concentrations of zinc (Zn) in animal tissues are known to be linked to life history, physiology and reproduction and may be retained in incremental growth structures. This study reconstructed lifetime Zn concentrations in teeth (n = 93) of female Pacific walruses (Odobenus rosmarus divergens) collected from 1932-2016. Zn displayed a characteristic pattern of accumulation, with a change point marking the beginning of a lifelong, linear increase in Zn concentrations. We hypothesized that this change point marks the onset of reproductive maturity. The age at which the change point occurred (agecp) was estimated by counting tooth cementum growth layers. These estimates closely matched literature values of timing of first ovulation in female walruses. Total number of ovulations (estimated from ovary corpora counts from paired tooth/ovary specimens) was closely related to reproductive lifespan (total lifespan - agecp; R2 = 0.70). Further, agecp tracked changes in Pacific walrus population size as a proportion of carrying capacity, decreasing when the population was depleted by commercial hunting and peaking when carrying capacity was exceeded. This novel approach will aid walrus management, and is likely applicable to other species, offering a potentially powerful tool for research, management and conservation of wildlife populations.

中文翻译：

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雌性海象牙齿中的锌浓度反映了生殖成熟的开始。

成熟年龄是许多人口统计模型中的一个重要参数，对于某些物种，使用传统方法可能难以获得。增量生长结构充当生物档案，记录整个生物体生命中的信息，并可能允许重建生命史事件。众所周知，动物组织中的锌 (Zn) 浓度与生活史、生理和繁殖有关，并且可能保留在增量生长结构中。本研究重建了 1932 年至 2016 年收集的雌性太平洋海象（Odobenus rosmarus divergens）牙齿（n = 93）中的终生锌浓度。锌显示出一种特征性的积累模式，一个变化点标志着锌浓度终生线性增加的开始。我们假设这个变化点标志着生殖成熟的开始。通过计算牙骨质生长层来估计发生变化点的年龄（agecp）。这些估计值与雌性海象第一次排卵时间的文献值非常吻合。排卵总数（根据配对牙齿/卵巢标本的卵巢语料库计数估计）与生殖寿命密切相关（总寿命 - agecp；R2 = 0.70）。此外，agecp 跟踪太平洋海象种群规模的变化，作为承载能力的比例，当种群因商业狩猎而耗尽时减少，当超过承载能力时达到峰值。这种新方法将有助于海象管理，并可能适用于其他物种，为研究提供潜在的强大工具，