Siracusa Erin R, Pavez-Fox Melissa A, Negron-Del Valle Josué E, Phillips Daniel, Platt Michael L, Snyder-Mackler Noah, Higham James P, Brent Lauren J N, Silk Matthew J
School of Psychology, Centre for Research in Animal Behaviour, University of Exeter, Exeter, UK.
Department of Psychology and Neuroscience, University of St Andrews, UK.
bioRxiv. 2024 Oct 22:2024.03.09.584237. doi: 10.1101/2024.03.09.584237.
The benefits of social living are well established, but sociality also comes with costs, including infectious disease risk. This cost-benefit ratio of sociality is expected to change across individuals' lifespans, which may drive changes in social behaviour with age. To explore this idea, we combine data from a group-living primate for which social ageing has been described with epidemiological models to show that having lower social connectedness when older can protect against the costs of a hypothetical, directly transmitted endemic pathogen. Assuming no age differences in epidemiological characteristics (susceptibility to, severity, and duration of infection), older individuals suffered lower infection costs, which was explained largely because they were less connected in their social networks than younger individuals. This benefit of 'social ageing' depended on epidemiological characteristics and was greatest when infection severity increased with age. When infection duration increased with age, social ageing was beneficial only when pathogen transmissibility was low. Older individuals benefited most from having a lower frequency of interactions (strength) and network embeddedness (closeness) and benefited less from having fewer social partners (degree). Our study provides a first examination of the epidemiology of social ageing, demonstrating the potential for pathogens to influence evolutionary dynamics of social ageing in natural populations.
群居生活的益处已得到充分证实，但群居也有代价，包括传染病风险。这种群居生活的成本效益比预计会在个体的整个生命周期中发生变化，这可能会推动社会行为随年龄的改变。为了探究这一观点，我们将来自一种群居灵长类动物的数据与流行病学模型相结合，该灵长类动物的社会老龄化情况已有描述，结果表明，年长时社会联系较少可以抵御一种假设的直接传播的地方病原体带来的成本。假设在流行病学特征（易感性、严重程度和感染持续时间）上不存在年龄差异，年长个体遭受的感染成本较低，这在很大程度上是因为他们在社交网络中的联系比年轻个体少。“社会老龄化”的这种益处取决于流行病学特征，当感染严重程度随年龄增加时最为显著。当感染持续时间随年龄增加时，只有在病原体传播性较低的情况下，社会老龄化才有益。年长个体从较低的互动频率（强度）和网络嵌入性（紧密程度）中受益最大，而从较少的社会伙伴（度数）中受益较少。我们的研究首次对社会老龄化的流行病学进行了考察，证明了病原体影响自然种群中社会老龄化进化动态的可能性。
