In many animal species, mothers eat some of their own eggs. While this filial egg cannibalism can have profound impacts on both parental and offspring fitness, it remains unclear whether this behaviour is a simple by-product of a generally low maternal investment in egg care and whether it is determined before or after egg production. Here, we addressed these questions in the European earwig, Forficula auricularia, an insect in which females vary in their level of investment in egg care and in their expression of egg cannibalism. Using a cross-fostering experiment, we investigated the benefits of egg cannibalism for mothers, the potential association between egg cannibalism and egg care, and whether egg cannibalism is a maternal strategy that is determined before or after egg laying. Our results first revealed that egg cannibalism provided direct benefits to mothers, as the females that consumed some of their eggs increased their investment in future reproduction. We then showed that egg cannibalism was independent of the level of maternal investment in two important forms of egg care (egg defence and the time taken to return after a simulated predator attack). Overall, this suggests that access to egg cannibalism may select for mothers to remain with their eggs, independent of the potential benefits of care for the eggs. Finally, we demonstrated that the number of eggs received, but not the number of eggs produced by foster mothers, determined the level of egg cannibalism. This highlights that egg cannibalism is determined after egg laying and is not the outcome of anticipatory maternal effects. Overall, these findings provide novel insights into our understanding of the early evolution of parental care, as they suggest that the direct benefits of filial egg cannibalism for mothers could have promoted egg attendance from an ancestral egg abandonment state.

中文翻译：

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欧洲蠼螋的卵子同类相食：其决定因素和对母体卵子护理演变的影响

在许多动物物种中，母亲会吃一些自己的蛋。虽然这种孝顺的卵子同类相食会对父母和后代的健康产生深远的影响，但目前尚不清楚这种行为是否是母体对卵子护理投资普遍较低的简单副产品，以及它是在产卵之前还是之后决定的。在这里，我们在欧洲蝾螈中解决了这些问题， Forficula auricularia 是一种昆虫，其中雌性在鸡蛋护理方面的投资水平和鸡蛋同类相食的表现各不相同。通过交叉抚养实验，我们调查了同类相食对母亲的好处、同类相食与鸡蛋护理之间的潜在关联，以及同类相食是否是一种在产卵之前或之后确定的母性策略。我们的研究结果首先表明，同类相食给母亲带来了直接的好处，因为食用了一些卵的雌性增加了对未来繁殖的投资。然后我们证明了鸡蛋同类相食与母体在两种重要的鸡蛋护理形式（鸡蛋防御和模拟捕食者攻击后返回所需的时间）中的投资水平无关。总体而言，这表明发生卵子同类相食可能会选择母亲留在卵子旁，而与照顾卵子的潜在好处无关。最后，我们证明了收到的鸡蛋数量，而不是寄养母亲生产的鸡蛋数量，决定了鸡蛋同类相食的程度。这突出表明，鸡蛋同类相食是在产卵后决定的，而不是预期的母体效应的结果。全面的，