Clark Casey T, Horstmann Lara, Misarti Nicole
Water and Environmental Research Center, University of Alaska Fairbanks, 1764 Tanana Loop, Fairbanks, AK 99775-5860, USA.
College of Fisheries and Ocean Sciences, University of Alaska Fairbanks, 2150 Koyukuk Drive, Fairbanks, AK 99775-7220, USA.
Conserv Physiol. 2020 Apr 13;8(1):coaa029. doi: 10.1093/conphys/coaa029. eCollection 2020.
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 ( = 93) of female Pacific walruses () 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 (age) 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 - age; R = 0.70). Further, age 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.
成熟年龄是许多人口统计学模型中的一个重要参数，对于某些物种来说，使用传统方法很难获得该参数。增量生长结构就像生物档案，记录着生物体一生的信息，并可能有助于重建生活史事件。已知动物组织中的锌（Zn）浓度与生活史、生理和繁殖有关，并且可能会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（ = 93）牙齿中的终生锌浓度。锌呈现出一种特征性的积累模式，有一个变化点标志着锌浓度开始终生呈线性增加。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变化点出现时的年龄（年龄）。这些估计值与雌性海象首次排卵时间的文献值密切匹配。排卵总数（根据配对的牙齿/卵巢标本的卵巢黄体计数估计）与生殖寿命（总寿命 - 年龄；R = 0.70）密切相关。此外，年龄跟踪了太平洋海象种群数量相对于承载能力的变化，当种群因商业捕猎而减少时年龄下降，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，并且可能适用于其他物种，为野生动物种群的研究、管理和保护提供了一个潜在的有力工具。
