How to study parasites and host migration: a roadmap for empiricists

Abstract

Animal migration (round‐trip, predictable movements) takes individuals across space and time, bringing them into contact with new communities of organisms. In particular, migratory movements shape (and are shaped by) the costs and risk of parasite transmission. Unfortunately, our understanding of how migration and parasite infection interact has not proceeded evenly. Although numerous conceptual frameworks (e.g. mathematical models) have been developed, most empirical evidence of migration–parasite interactions are drawn from pre‐existing empirical studies that were conducted using other conceptual frameworks, which limits our understanding. Here, we synthesise and analyse existing work, and then provide a roadmap for future (especially empirical) studies. First, we synthesise the conceptual frameworks that have been developed to understand interactions between migration and parasites (e.g. migratory exposure, escape, allopatry, recovery, culling, separation, stalling and relapse). Second, we highlight current challenges to studying migration and parasites empirically, and to integrating empirical and theoretical perspectives, particularly emphasizing the challenge of feedback loops. Finally, we provide a guide to overcoming these challenges in empirical studies, using comparative, observational and experimental approaches. Beyond guiding future empirical work, this review aims to inspire stronger collaboration between empiricists and theorists studying the intersection of migration and parasite infection. Such collaboration will help overcome current limits to our understanding of how migration and parasites interact, and allow us to predict how these critical ecological processes will change in the future.

A skewed literature: Few studies evaluate the contribution of predation‐risk effects to natural field patterns

“…The term 'observational studies' (Binning et al, 2022;Underwood et al, 2000;Vellend, 2016) and related terms such as 'strictly observational approaches' (Sagarin & Pauchard, 2010), are sometimes used to describe studies that include observing unmanipulated patterns of variables across space and/or time to contribute to the study of a process. The term observational study is too vague for our purposes.…”

Editorial: Ecophysiological adaptations associated with animal migration

“…For example, gut parasites have been thought to disrupt osmoregulation in salmon moving from fresh-to saltwater, but Finlay et al did not find such effects, suggesting that fish either cope with the presence of parasites or that negative effects become apparent at a later stage of infection. Further studies investigating varying immune function and its interactions with infection rates are of paramount importance to understand how parasite and disease exposure influence migratory animals (Binning et al, 2022), particularly in the context of predicting future disease outbreaks and pandemics (Carlson et al, 2022).…”

Gaps in modelling animal migration with evolutionary game theory: infection can favour the loss of migration

“…land use change, urbanization, habitat encroachment, invasive species, climate change [8][9][10][11]. Migration has evolved in many species as a way for individuals to maximize their fitness in seasonal or otherwise variable environments, allowing individuals to track favourable climates, resources and/or minimize negative biotic interactions (such as predation, competition and parasitism [12,13]). Unfortunately, animal migrations are declining globally due to anthropogenic changes such as habitat destruction and barriers [4].…”

“…For instance, the introduction of non-native perennial milkweed ( Asclepia curassavica ) in southern parts of the United States has promoted a shift to residency in formerly migratory populations of monarch butterflies ( Danaus plexippus ; [14,15]). These drivers of migratory loss are less studied and understood, perhaps because there are inherent challenges to studying both species interactions and migratory behaviours in natural populations [13].…”