Evolution & Ecology Research Centre, School of Biological and Environmental Sciences, University of New South Wales, Sydney, 2052 NSW, Australia.
BMC Biol. 2023 May 12;21(1):107. doi: 10.1186/s12915-023-01603-4.
Finding the optimal balance between survival and reproduction is a central puzzle in life-history theory. The terminal investment hypothesis predicts that when individuals encounter a survival threat that compromises future reproductive potential, they will increase immediate reproductive investment to maximise fitness. Despite decades of research on the terminal investment hypothesis, findings remain mixed. We examined the terminal investment hypothesis with a meta-analysis of studies that measured reproductive investment of multicellular iteroparous animals after a non-lethal immune challenge. We had two main aims. The first was to investigate whether individuals, on average, increase reproductive investment in response to an immune threat, as predicted by the terminal investment hypothesis. We also examined whether such responses vary adaptively on factors associated with the amount of reproductive opportunities left (residual reproductive value) in the individuals, as predicted by the terminal investment hypothesis. The second was to provide a quantitative test of a novel prediction based on the dynamic threshold model: that an immune threat increases between-individual variance in reproductive investment. Our results provided some support for our hypotheses. Older individuals, who are expected to have lower residual reproductive values, showed stronger mean terminal investment response than younger individuals. In terms of variance, individuals showed a divergence in responses, leading to an increase in variance. This increase in variance was especially amplified in longer-living species, which was consistent with our prediction that individuals in longer-living species should respond with greater individual variation due to increased phenotypic plasticity. We find little statistical evidence of publication bias. Together, our results highlight the need for a more nuanced view on the terminal investment hypothesis and a greater focus on the factors that drive individual responses.
在生命史理论中，找到生存和繁殖之间的最佳平衡是一个核心难题。终末投资假说预测，当个体遇到危及未来繁殖潜力的生存威胁时，它们会增加当前的繁殖投资，以最大限度地提高适应性。尽管对终末投资假说进行了几十年的研究，但研究结果仍存在分歧。我们通过对测量多细胞多次生殖动物在非致死性免疫挑战后繁殖投资的研究进行荟萃分析，检验了终末投资假说。我们有两个主要目标。第一个目标是调查个体是否平均会根据终末投资假说增加繁殖投资，以应对免疫威胁。我们还研究了这种反应是否会根据个体剩余繁殖价值（个体剩余繁殖价值）相关因素进行适应性变化，这是终末投资假说所预测的。第二个目标是根据动态阈值模型提供一个新的预测的定量检验：免疫威胁会增加繁殖投资的个体间方差。我们的研究结果为我们的假设提供了一些支持。预期剩余繁殖价值较低的老年个体表现出比年轻个体更强的终末投资反应。就方差而言，个体表现出反应的分歧，导致方差增加。这种方差的增加在寿命较长的物种中尤其放大，这与我们的预测一致，即寿命较长的物种中的个体由于表型可塑性增加，应该会做出更大的个体变异反应。我们发现几乎没有证据表明存在发表偏倚。总的来说，我们的研究结果强调需要对终末投资假说进行更细致的分析，并更加关注驱动个体反应的因素。
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