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

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.