Filial cannibalism leads to chronic nest failure of eastern hellbender salamanders (Cryptobranchus alleganienesis)

These data and code support the results in our accompanying manuscript. In species that provide parental care, parents will sometimes cannibalize their own young. Here, we quantified the frequency of whole-clutch filial cannibalism in a species of giant salamander (eastern hellbender; Cryptobranchus alleganienesis) that has experienced precipitous population declines with unknown causes. We used underwater, artificial nesting shelters deployed across a gradient of upstream forest cover to assess the fates of 182 nests at 10 sites over 8 years. We found strong evidence that nest failure rates increased at sites with low riparian forest cover in the upstream catchment. At several sites, reproductive failure was 100%, mainly due to cannibalism by the caring male. The high incidence of filial cannibalism at degraded sites was not explained by evolutionary hypotheses for filial cannibalism based on adult body condition or low reproductive value of clutches. Instead, larger clutches at degraded sites were most vulnerable to cannibalism.  We hypothesize that high frequencies of filial cannibalism of large clutches in areas with low forest cover could be related to changes in water chemistry or siltation that influence parental physiology or that reduce viability of eggs. Importantly, our results identify a possible mechanism contributing to population declines and observed geriatric age structure in this imperiled species.

Methods
We used underwater, artificial nesting shelters deployed across a gradient of upstream forest cover to assess the fates of 182 nests at 10 sites over 8 years. We measured nest success using images and videos taken at different times of the year. The data included here have been checked for quality control. The analysis is available in the R script.

本数据集及配套代码可支撑随附手稿中的研究结论。
在具备育幼行为的物种中，亲代偶尔会出现同类相食幼崽的现象。本研究针对一种种群数量骤降且致因不明的巨型蝾螈物种——东方隐鳃鲵（eastern hellbender; Cryptobranchus alleganienesis），量化了其整窝亲子相食行为（whole-clutch filial cannibalism）的发生频率。我们在8年的研究周期内，于10个研究位点布设了覆盖上游森林覆盖梯度的水下人工巢箱，以此追踪10个位点共计182窝卵的存活结局。研究结果表明，上游集水区内河岸森林覆盖率较低的位点，其巢窝失败率显著升高，该结论具备强统计学支撑。在部分研究位点中，繁殖完全失败（成功率为0%），其主要诱因为育幼雄体的同类相食行为。退化位点中高发的亲子相食行为，无法通过基于成体身体状况或窝卵低繁殖价值的亲子相食进化假说得到合理解释。与之相反，退化位点中的大型窝卵最易遭受同类相食。我们提出如下假说：在森林覆盖率较低的区域，大型窝卵的亲子相食行为高发，可能与影响亲代生理机能或降低卵孵化存活率的水体化学性质变化或泥沙淤积有关。值得注意的是，本研究结果揭示了一种潜在机制，可解释该濒危物种的种群数量下降以及野外观测到的老龄化种群结构。

研究方法
我们在8年的研究周期内，于10个研究位点布设了覆盖上游森林覆盖梯度的水下人工巢箱，以此追踪10个位点共计182窝卵的存活结局。通过在一年中不同时段采集的图像与视频，我们对巢窝成功率进行了量化评估。本数据集已完成全面的质量管控核查。相关分析代码可在配套R脚本中获取。