Parasites and Host Performance: Incorporating Infection into Our Understanding of Animal Movement

Abstract

Studies of animal locomotion and movement largely assume that individuals are healthy and performing to the best of their abilities in ways which are adapted to their survival. However, wild animals face numerous ecological challenges that can compromise their health, reduce their performance capacity, impair their movement abilities and, ultimately, lower their fitness. By diverting resources and increasing host energetic demands, parasites, bacteria, and viruses (hereafter parasites) can dramatically influence the ways in which their hosts allocate energy to movement. Yet, the role of parasites in influencing animal locomotor performance and movement remains relatively unexplored, perhaps because animals often hide outward signs of sickness, and parasites tend to be small and inconspicuous to researchers. Here, we review how parasite infection can alter host locomotor performance via impacts on host morphology and physiology. We also give examples of behavioral strategies that some hosts employ to help overcome the disadvantages imposed by infection. Finally, we discuss how parasites can lead to both increased and decreased host movement patterns, either as an adaptive strategy for the host or due to manipulation by the parasite. The dynamic interplay between host movement (such as migration and dispersal) and infection has profound consequences for population and ecosystem-level processes that are influenced by movement. Acknowledging the important functional role played by parasites in driving the evolution of host locomotor performance and behavior is a critical step toward developing a comprehensive understanding of the causes and consequences of animal movement.

Metrics matter: the effect of parasite richness, intensity and prevalence on the evolution of host migration

“…It seems reasonable to expect that a combination of parasite diversity (quantified by 'richness', or other variant), prevalence and intensity would drive selection on migration differently in different systems. For example, infection intensity might be more important for ectoparasites under some circumstances but not others; species that fly or swim experience more drag than those that walk [54], with drag amplified by the presence of ectoparasites [15]. Other parasites might have a threshold effect, where infection beyond a certain intensity is lethal [55].…”

“…Both early and modern conceptions of migration as a refuge behaviour focus on climate as a driving factor [8,9]. However, these seasonal movements may also be driven by predators [10,11], parasitoids [12], or parasites and pathogens [13].The role of parasites in determining host ecology and behaviour is becoming increasingly recognized [14,15]. Parasites (which here we define broadly to include both macroparasites and microparasites, as per [16]) in particular can shape migration patterns in several distinct ways.…”

Schistocephalusparasite infection alters sticklebacks’ movement ability and thereby shapes social interactions

“…Parasitism is ubiquitous across the animal kingdom, with parasites often exerting considerable influence on their hosts, consuming energy, and inducing morphological, physiological, and behavioural changes [1][2][3]. Parasites have been best studied in terms of their ecological and evolutionary effects on hosts [1,4], but may also have large effects on host behaviour [2].…”

Recovery from infection is more likely to favour the evolution of migration than social escape from infection

“…Yet, theoretical and empirical evidence that parasites influence the migratory decisions of their hosts is increasing (Daversa, Fenton, Dell, Garner, & Manica, 2017; Daversa, Manica, Bosch, Jolles, & Garner, 2018; Halttunen et al, 2018; Hegemann et al, 2018; Shaw & Binning, 2016; Shaw, Craft, Zuk, & Binning, 2019b). Predicting how infection may influence host migration requires not only accounting for changing infection risk, but also being explicit about the mechanism linking infection and migration—infection could be predicted to either increase or decrease host migration depending on the circumstance (Binning, Shaw, & Roche, 2017). Here, we focus on two mechanisms where migration provides infection‐related benefits to hosts, although we note that migration can have infection‐related costs for some host species in terms of increased infection probability (Kelly et al, 2016), increased parasite richness (Figuerola & Green, 2000; Koprivnikar & Leung, 2015; Teitelbaum, Huang, Hall, & Altizer, 2018), amplified costs of infection (Risely, Klaassen, & Hoye, 2018); or even simultaneous costs and benefits depending on the infection metric considered (Shaw, Sherman, Barker, & Zuk, 2018).…”