Sweeny Amy R, Corripio-Miyar Yolanda, Bal Xavier, Hayward Adam D, Pilkington Jill G, McNeilly Tom N, Nussey Daniel H, Kenyon Fiona
Institute of Evolutionary Biology, University of Edinburgh, Edinburgh, UK.
Moredun Research Institute, Penicuik, UK.
Parasitology. 2022 Feb 3;149(5):1-12. doi: 10.1017/S0031182021001980.
Within-year variation in infection is a ubiquitous feature of natural populations, but is determined by a complex interplay of environmental, parasitological and host factors. At the same time, co-infection is the norm in the wild. Longitudinal dynamics of co-infecting parasites may therefore be further complicated by covariation across multiple parasites. Here, we used fecal parasite egg and oocyst counts collected repeatedly from individually marked wild Soay sheep to investigate seasonal dynamics of six gastrointestinal parasite groups. Prevalence and abundance tended to be higher in spring and summer, and abundance was higher in lambs compared to adults. We found that within-year variation in highly prevalent strongyle nematode counts was dependent on adult reproductive status, where reproductive ewes had distinct dynamics compared to males and barren ewes. For similarly prevalent coccidia we found an overall peak in oocyst counts in spring but no differences among males, barren and pregnant ewes. Using multivariate mixed-effects models, we further show that apparent positive correlation between strongyle and coccidia counts was driven by short-term within-individual changes in both counts rather than long-term among-individual covariation. Overall, these results demonstrate that seasonality varies across demographic and parasite groups and highlight the value of investigating co-infection dynamics over time.
年内感染的变化是自然种群中普遍存在的特征，但它由环境、寄生虫学和宿主因素的复杂相互作用所决定。与此同时，共同感染在野外是常态。因此，多种寄生虫之间的协变可能会使共同感染寄生虫的纵向动态进一步复杂化。在这里，我们使用从个体标记的野生索艾羊身上反复收集的粪便寄生虫卵和卵囊计数，来研究六个胃肠道寄生虫组的季节性动态。春季和夏季的患病率和丰度往往更高，与成年羊相比，羔羊的丰度更高。我们发现，高度流行的圆线虫计数的年内变化取决于成年羊的繁殖状态，与雄性羊和未受孕母羊相比，受孕母羊具有明显不同的动态变化。对于同样流行的球虫，我们发现卵囊计数在春季总体达到峰值，但雄性羊、未受孕母羊和受孕母羊之间没有差异。使用多变量混合效应模型，我们进一步表明，圆线虫和球虫计数之间明显的正相关是由两种计数在个体内的短期变化驱动的，而不是由个体间的长期协变驱动的。总体而言，这些结果表明，季节性在不同的种群统计学特征和寄生虫组中有所不同，并突出了随着时间推移研究共同感染动态的价值。
