Department of Zoology, University of Otago, P.O. Box 56, Dunedin, New Zealand.
Biol Rev Camb Philos Soc. 2021 Aug;96(4):1331-1348. doi: 10.1111/brv.12704. Epub 2021 Mar 4.
Migrations, i.e. the recurring, roundtrip movement of animals between distant and distinct habitats, occur among diverse metazoan taxa. Although traditionally linked to avoidance of food shortages, predators or harsh abiotic conditions, there is increasing evidence that parasites may have played a role in the evolution of migration. On the one hand, selective pressures from parasites can favour migratory strategies that allow either avoidance of infections or recovery from them. On the other hand, infected animals incur physiological costs that may limit their migratory abilities, affecting their speed, the timing of their departure or arrival, and/or their condition upon reaching their destination. During migration, reduced immunocompetence as well as exposure to different external conditions and parasite infective stages can influence infection dynamics. Here, we first explore whether parasites represent extra costs for their hosts during migration. We then review how infection dynamics and infection risk are affected by host migration, thereby considering parasites as both causes and consequences of migration. We also evaluate the comparative evidence testing the hypothesis that migratory species harbour a richer parasite fauna than their closest free-living relatives, finding general support for the hypothesis. Then we consider the implications of host migratory behaviour for parasite ecology and evolution, which have received much less attention. Parasites of migratory hosts may achieve much greater spatial dispersal than those of non-migratory hosts, expanding their geographical range, and providing more opportunities for host-switching. Exploiting migratory hosts also exerts pressures on the parasite to adapt its phenology and life-cycle duration, including the timing of major developmental, reproduction and transmission events. Natural selection may even favour parasites that manipulate their host's migratory strategy in ways that can enhance parasite transmission. Finally, we propose a simple integrated framework based on eco-evolutionary feedbacks to consider the reciprocal selection pressures acting on migratory hosts and their parasites. Host migratory strategies and parasite traits evolve in tandem, each acting on the other along two-way causal paths and feedback loops. Their likely adjustments to predicted climate change will be understood best from this coevolutionary perspective.
迁徙，即动物在遥远而不同的栖息地之间反复往返的运动，发生在各种后生动物类群中。尽管传统上与避免食物短缺、捕食者或恶劣的非生物条件有关，但越来越多的证据表明寄生虫可能在迁徙的进化中发挥了作用。一方面，寄生虫的选择压力可能有利于迁徙策略，使动物可以避免感染或从感染中恢复。另一方面，受感染的动物会产生生理成本，这可能会限制它们的迁徙能力，影响它们的速度、出发或到达的时间，以及/或到达目的地时的状态。在迁徙过程中，免疫能力下降以及暴露于不同的外部条件和寄生虫感染阶段会影响感染动态。在这里，我们首先探讨寄生虫是否代表宿主在迁徙过程中的额外成本。然后，我们回顾了宿主迁徙如何影响感染动态和感染风险，从而将寄生虫视为迁徙的原因和结果。我们还评估了比较证据，以检验迁徙物种比其最接近的自由生活的近亲拥有更丰富的寄生虫动物区系的假说，发现该假说得到了普遍支持。然后，我们考虑了宿主迁徙行为对寄生虫生态学和进化的影响，这方面的关注较少。与非迁徙宿主的寄生虫相比，迁徙宿主的寄生虫可能会实现更大的空间扩散，扩大其地理范围，并为宿主转换提供更多机会。利用迁徙宿主也会对寄生虫施加压力，促使其适应其物候和生命周期持续时间，包括主要发育、繁殖和传播事件的时间。自然选择甚至可能有利于操纵宿主迁徙策略的寄生虫，从而增强寄生虫的传播。最后，我们提出了一个简单的综合框架，基于生态进化反馈，来考虑对迁徙宿主及其寄生虫施加的相互选择压力。宿主迁徙策略和寄生虫特征协同进化，彼此沿着双向因果路径和反馈回路相互作用。从这种共同进化的角度来看，它们对预测气候变化的可能调整将得到最好的理解。
