Normandeau Jacalyn, Kutz Susan J, Hebblewhite Mark, Merrill Evelyn H
University of Alberta, Edmonton, Alberta, T6G 2R3, Canada.
Department of Ecosystem and Public Health, Faculty of Veterinary Medicine, University of Calgary, Calgary, Alberta, T2N 4Z6, Canada.
Int J Parasitol Parasites Wildl. 2020 May 12;12:76-84. doi: 10.1016/j.ijppaw.2020.05.002. eCollection 2020 Aug.
Migration is typically thought to be an evolved trait driven by responses to forage or predation, but recent studies have demonstrated avoidance of parasitism can also affect success of migratory tactics within a population. We evaluated hypotheses of how migration alters parasite exposure in a partially migratory elk () population in and adjacent to Banff National Park, Alberta, Canada. Equal numbers of elk remain year-round on the winter range or migrate to summer range. We quantified diversity and abundance of parasites in faecal elk pellets, and prevalence (number of infected individuals) and intensity (egg counts) of giant liver fluke eggs () in faeces across migratory tactics. We tested whether giant liver fluke intensity in faeces was affected by elk use of wetlands, elevation, forage biomass, and elk concentration in the previous summer. We rejected the "migratory escape" hypothesis that suggests migration allowed elk to escape parasite exposure because migrant elk had the highest richness and evenness of parasite groups. We also rejected the hypothesis that prevalence was highest at highest summer densities because higher-density resident elk had the lowest diversity and giant liver fluke egg presence and intensity. Instead, the high prevalence and intensity of giant liver flukes in migrants was consistent with both the hypothesis of "environmental tracking", because elk that migrated earlier may expose themselves to favourable parasite conditions, and with the "environmental sampling" hypothesis, because giant liver fluke intensity increased with increased exposure to secondary host habitat (i.e., wetland). Our results indicate that differential exposure of different migratory tactics that leave the winter range has a greater influence on parasites than the concentration of elk that reside on the winter range year-round.
迁移通常被认为是一种进化特征，由对觅食或捕食的反应所驱动，但最近的研究表明，避免寄生也会影响种群内迁移策略的成功。我们评估了在加拿大艾伯塔省班夫国家公园及其周边的一个部分迁移的麋鹿种群中，迁移如何改变寄生虫暴露的假设。数量相等的麋鹿全年留在冬季栖息地或迁移到夏季栖息地。我们对麋鹿粪便中的寄生虫多样性和丰度进行了量化，并对不同迁移策略下粪便中巨片形吸虫卵的流行率（感染个体数量）和强度（虫卵计数）进行了量化。我们测试了粪便中巨片形吸虫的强度是否受到麋鹿对湿地的利用、海拔、觅食生物量以及前一个夏天麋鹿聚集程度的影响。我们拒绝了“迁移逃避”假说，该假说认为迁移使麋鹿能够逃避寄生虫暴露，因为迁移的麋鹿寄生虫种类的丰富度和均匀度最高。我们还拒绝了流行率在夏季最高密度时最高的假说，因为高密度的常驻麋鹿寄生虫多样性最低，且巨片形吸虫卵的存在和强度也最低。相反，迁移麋鹿中巨片形吸虫的高流行率和强度与“环境追踪”假说一致，因为较早迁移的麋鹿可能使自己暴露于有利的寄生虫环境中，也与“环境采样”假说一致，因为巨片形吸虫的强度随着对中间宿主栖息地（即湿地）暴露的增加而增加。我们的结果表明，离开冬季栖息地的不同迁移策略的差异暴露对寄生虫的影响比全年留在冬季栖息地的麋鹿聚集程度更大。
