Parental care benefits offspring but comes with costs. To optimize the trade-off of costs and benefits, parents should adjust care based on intrinsic and/or extrinsic conditions. The harm to offspring hypothesis suggests that parents should invest more in younger offspring than older offspring because younger offspring are more vulnerable. However, this hypothesis has rarely been comprehensively tested, as many studies only reveal an inverse correlation between parental care and offspring age, without directly testing the effects of offspring age on their vulnerability. To test this hypothesis, we studied Kurixalus eiffingeri, an arboreal treefrog with paternal care. We first performed a field survey by monitoring paternal care during embryonic development. Subsequently, we conducted a field experiment to assess the prevalence of egg predators (a semi-slug, Parmarion martensi) and the plasticity of male care. Finally, we conducted a laboratory experiment to assess how embryo age affects predation by P. martensi. Our results showed that (1) male attendance and brooding frequency affected embryo survival, and (2) males attended and brooded eggs more frequently in the early stage than in the late stage. The experimental results showed that (3) males increased attendance frequency when the predators were present, and (4) the embryonic predation by the semi-slug during the early was significantly higher than in the late stage. Our findings highlight the importance of paternal care to embryo survival, and the care behavior is plastic. Moreover, our results provide evidence consistent with the predictions of the harm to offspring hypothesis, as males tend to care more for younger offspring which are more vulnerable.

中文翻译：

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父系抚育可塑性：在树栖繁殖的树蛙中，雄性更关心早期发育的胚胎，而不是晚期发育的胚胎


父母的照顾对后代有利，但也有代价。为了优化成本和收益的权衡，父母应根据内在和/或外在条件调整护理。对后代的伤害假说表明，父母应该比年长的后代更多地投资于年幼的后代，因为年幼的后代更容易受到伤害。然而，这一假设很少得到全面检验，因为许多研究仅揭示了父母照顾与后代年龄之间的负相关关系，而没有直接检验后代年龄对其脆弱性的影响。为了验证这一假设，我们研究了 Kurixalus eiffingeri，一种由父亲照顾的树栖树蛙。我们首先通过监测胚胎发育过程中父亲的护理进行了实地调查。随后，我们进行了一项现场实验，以评估卵捕食者（一种半蛞蝓，Parmarion martensi）的普遍性和雄性护理的可塑性。最后，我们进行了一项实验室实验来评估胚胎年龄如何影响马氏体虾的捕食。我们的结果表明，（1）雄性出勤率和育雏频率影响胚胎存活率，（2）雄性在早期阶段的出勤率和育雏频率高于晚期。实验结果表明：（3）当捕食者存在时，雄性出现的频率增加；（4）半蛞蝓胚胎早期的捕食量显着高于晚期。我们的研究结果强调了父亲护理对胚胎存活的重要性，并且护理行为是可塑的。此外，我们的结果提供了与后代伤害假说的预测一致的证据，因为男性往往更关心更脆弱的年轻后代。