Migratory animals feel the cost of getting sick: A meta‐analysis across species

Abstract

Abstract1. Migratory animals are widely assumed to play an important role in the long-distance dispersal of parasites, and are frequently implicated in the global spread of zoonotic pathogens such as avian influenzas in birds and Ebola viruses in bats.However, infection imposes physiological and behavioural constraints on hosts that may act to curtail parasite dispersal via changes to migratory timing ("migratory separation") and survival ("migratory culling").2. There remains little consensus regarding the frequency and extent to which migratory separation and migratory culling may operate, despite a growing recognition of the importance of these mechanisms in regulating transmission dynamics in migratory animals.3. We quantitatively reviewed 85 observations extracted from 41 studies to examine how both infection status and infection intensity are related to changes in body stores, refuelling rates, movement capacity, phenology and survival in migratory hosts across taxa.4. Overall, host infection status was weakly associated with reduced body stores, delayed migration and lower survival, and more strongly associated with reduced movement. Infection intensity was not associated with changes to host body stores, but was associated with moderate negative effects on movement, phenology and survival.5. In conclusion, we found evidence for negative effects of infection on host phenology and survival, but the effects were relatively small. This may have implications for the extent to which migratory separation and migratory culling act to limit parasite dispersal in migratory systems. We propose a number of recommendations for future research that will further advance our understanding of how migratory separation and migratory culling may shape host-parasite dynamics along migratory routes globally. K E Y W O R D Sdisease ecology, host-pathogen dynamics, migratory culling, migratory separation, parasite ecology, pathogen dispersal, zoonoses

On the relationship between body condition and parasite infection in wildlife: a review and meta‐analysis

“…We fit the REMs with restricted maximum likelihood (REML) to obtain unbiased estimates of variance components, from which we calculated I 2 to quantify the contribution of true heterogeneity to total variance in effect size (Nakagawa & Santos 2012;Senior et al 2016). We repeated analyses on observational data divided by intensity (n = 359) and infection status (n = 143) to account for differences in the condition-infection relationship that could arise from how parasitism was measured (Risely et al 2018).…”

Immune function and blood parasite infections impact stopover ecology in passerine birds

“…Infections are known to hamper migration performance in a variety of taxa, including mammals (Mysterud et al 2016), insects (Bradley and Altizer 2005), fish (Sjöberg et al 2009) and birds (Risely et al 2018) and we recently demonstrated that an energetically costly mimicked bacterial infection increases stopover duration in songbirds (Hegemann et al 2018). However, there is no study investigating to what extent mild and/or chronic parasite infections impact stopover ecology in songbirds, which constitute the vast majority of avian migrants.…”

A mimicked bacterial infection prolongs stopover duration in songbirds—but more pronounced in short‐ than long‐distance migrants

“…Together with findings that individuals carrying infections can show poorer physical endurance (Bradley & Altizer, ), slower migration (Bradley & Altizer, ; van Gils et al., ) and move shorter distances (Sjöberg et al., ), this opens up the possibility that immune responses during migration form a major physiological mechanism for carry‐over effects between annual‐cycle stages (Studds & Marra, ). Effects of infections on migration have also been associated with lower rates of survival (Risely et al., ). Hence, this mechanism could also support the idea of migratory culling, that is selective removal of infected hosts during demanding migration journeys (Bradley & Altizer, ).…”

“…Consequently, it has been hypothesized that trade‐offs between immune function and refuelling rate exist, and this would increase stopover duration and hence reduce migration speed (Klaassen, Hoye, Nolet, & Buttemer, ). Indeed, observational studies suggest that pathogens can impair migration in insects (Bradley & Altizer, ), fish (Sjöberg, Petersson, Wickstrom, & Hansson, ) and birds (van Gils et al., ), and a recent meta‐analysis across taxa indicates that parasites and infection intensity negatively impact migration performance (Risely, Klaassen, & Hoye, ).…”

“…Indeed, observational studies suggest that pathogens can impair migration in insects (Bradley & Altizer, 2005), fish (Sjöberg, Petersson, Wickstrom, & Hansson, 2009) and birds (van Gils et al, 2007), and a recent meta-analysis across taxa indicates that parasites and infection intensity negatively impact migration performance (Risely, Klaassen, & Hoye, 2018).…”