Abstract

Frequent social interactions, proximity to conspecifics, and group density are main drivers of infections and parasite transmissions. However, recent theoretical and empirical studies suggest that the health benefits of sociality and group living can outweigh the costs of infection and help social individuals fight infections or increase their infection-related tolerance level. Here, we combine the advantage of studying artificially created social work groups with different demographic compositions with free-range feeding and social behaviours in semi-captive Asian elephants (Elephas maximus), employed in timber logging in Myanmar. We examine the link between gastro-intestinal nematode load (strongyles and Strongyloides spp.), estimated by faecal egg counts, and three different aspects of an elephant’s social world: individual solitary behaviour, work group size, and work group sex ratio. Controlling for sex, age, origin, time since last deworming treatment, year, human sampler bias, and individual identity, we found that infection by nematodes ranged from 0 to 2720 eggs/g between and within 26 male and 45 female elephants over the 4-year study period. However, such variation was not linked to any investigated measures of sociality in either males or females. Our findings highlight the need for finer-scale studies, establishing how sociality is limited by, mitigates, or protects against infection in different ecological contexts, to fully understand the mechanisms underlying these pathways.

Significance statement

Being social involves not only benefits, such as improved health, but also costs, including increased risk of parasitism and infectious disease. We studied the relationship between and three different sociality measures—solitary behaviour, group size, and the proportion of females to males within a group—and infection by gut nematodes (roundworms), using a unique study system of semi-captive working Asian elephants. Our system allows for observing how infection is linked to sociality measures across different social frameworks. We found that none of our social measures was associated with nematode infection in the studied elephants. Our results therefore suggest that here infection is not a large cost to group living, that it can be alleviated by the benefits of increased sociality, or that there are weak infection–sociality associations present which could not be captured and thus require finer-scale measures than those studied here. Overall, more studies are needed from a diverse range of systems that investigate specific aspects of social infection dynamics.

中文翻译：

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调查亚洲象线虫感染与三种社会性指标之间的关联

摘要

频繁的社交互动、接近同种动物和群体密度是感染和寄生虫传播的主要驱动因素。然而，最近的理论和实证研究表明，社交和群体生活的健康益处可以超过感染的成本，并帮助社会个体抵抗感染或提高他们与感染相关的耐受水平。在这里，我们将研究人工创建的具有不同人口构成的社会工作组的优势与在缅甸木材采伐中使用的半圈养亚洲象 ( Elephas maximus )的自由放养和社会行为相结合。我们检查了胃肠道线虫负荷（圆线虫和圆线虫属）之间的联系。)，根据粪便卵数和大象社会世界的三个不同方面进行估计：个体孤独行为、工作组规模和工作组性别比例。控制性别、年龄、起源、自上次驱虫治疗以来的时间、年份、人类采样器偏差和个体身份，我们发现线虫的感染范围为 0 到 2720 个卵/g，在 4 年中 26 头雄性大象和 45 头雌性大象之间- 年学习期。然而，这种变化与任何调查的男性或女性社会性措施无关。我们的研究结果强调需要进行更精细的研究，确定社会性如何在不同的生态环境中受到感染的限制、减轻或保护，以充分了解这些途径背后的机制。

意义陈述

社交不仅涉及好处，例如改善健康，还涉及成本，包括增加寄生和传染病的风险。我们使用一种独特的半圈养亚洲象研究系统，研究了三种不同的社会性指标——孤独行为、群体规模、群体中雌性与雄性的比例——以及肠道线虫（蛔虫）感染之间的关系。我们的系统允许观察感染如何与跨不同社会框架的社会性措施相关联。我们发现，我们的任何社会措施都与所研究大象的线虫感染无关。因此，我们的研究结果表明，这里的感染对集体生活来说并不是一个很大的成本，它可以通过增加社交的好处来缓解，或者存在无法捕获的弱感染 - 社会性关联，因此需要比这里研究的更精细的措施。总体而言，需要从各种系统中进行更多研究，以调查社会感染动态的特定方面。