Seasonal Effects on Great Ape Health: A Case Study of Wild Chimpanzees and Western Gorillas

Among factors affecting animal health, environmental influences may directly or indirectly impact host nutritional condition, fecundity, and their degree of parasitism. Our closest relatives, the great apes, are all endangered and particularly sensitive to infectious diseases. Both chimpanzees and western gorillas experience large seasonal variations in fruit availability but only western gorillas accordingly show large changes in their degree of frugivory. The aim of this study is to investigate and compare factors affecting health (through records of clinical signs, urine, and faecal samples) of habituated wild ape populations: a community (N = 46 individuals) of chimpanzees (Pan troglodytes) in Kanyawara, Kibale National Park (Uganda), and a western gorilla (G. gorilla) group (N = 13) in Bai Hokou in the Dzanga-Ndoki National Park (Central African Republic). Ape health monitoring was carried out in the wet and dry seasons (chimpanzees: July–December 2006; gorillas: April–July 2008 and December 2008–February 2009). Compared to chimpanzees, western gorillas were shown to have marginally greater parasite diversity, higher prevalence and intensity of both parasite and urine infections, and lower occurrence of diarrhea and wounds. Parasite infections (prevalence and load), but not abnormal urine parameters, were significantly higher during the dry season of the study period for western gorillas, who thus appeared more affected by the large temporal changes in the environment in comparison to chimpanzees. Infant gorillas were the most susceptible among all the age/sex classes (of both apes) having much more intense infections and urine blood concentrations, again during the dry season. Long term studies are needed to confirm the influence of seasonal factors on health and parasitism of these great apes. However, this study suggest climate change and forest fragmentation leading to potentially larger seasonal fluctuations of the environment may affect patterns of ape parasitism and further exacerbate health impacts on great ape populations that live in highly seasonal habitats.

在影响动物健康的诸多因素中，环境影响可直接或间接作用于宿主的营养状况、繁殖能力以及寄生感染程度。我们的近亲——类人猿（great apes）均处于濒危状态，且对传染性疾病尤为易感。黑猩猩与西部大猩猩均会经历果实可获得性的大幅季节性波动，但仅有西部大猩猩的食果性（frugivory）会随之发生显著变化。本研究旨在通过临床体征记录、尿液及粪便样本检测，调查并比较两个已习惯化的野生猿类种群的健康影响因素：分别是乌干达基巴莱国家公园卡尼瓦拉群落的黑猩猩（Pan troglodytes）种群（N=46只个体），以及中非共和国唐加-恩多基国家公园拜霍库的西部大猩猩（G. gorilla）种群（N=13只个体）。猿类健康监测分别在湿季与干季开展：黑猩猩的监测时段为2006年7月至12月；大猩猩的监测时段为2008年4月至7月，以及2008年12月至2009年2月。相较于黑猩猩，西部大猩猩的寄生虫多样性略高，寄生虫感染与尿液异常的检出率及感染强度均更高，而腹泻与伤口的发生率则更低。在本研究的干季，西部大猩猩的寄生虫感染（检出率与感染负荷）显著更高，但尿液参数未出现明显异常；相较于黑猩猩，西部大猩猩似乎更易受环境的大幅季节性变化影响。在两类猿类的所有年龄/性别组别中，幼年大猩猩的易感性最强，其感染强度更高且尿液血液浓度异常，这一现象同样出现在干季。仍需开展长期研究以确认季节性因素对这些类人猿的健康与寄生感染的影响。然而本研究表明，气候变化与森林碎片化可能导致环境季节性波动进一步加剧，进而改变猿类的寄生感染模式，并进一步加重栖息于高度季节性生境中的类人猿种群的健康负担。