Tick-tock, racing the clock: parasitism is associated with decreased sprint performance in the Eastern fence lizard

Host–parasite relationships are important components of ecological systems that influence the evolution of both hosts and parasites. High levels of ectoparasitic infections can disrupt host homeostasis, causing adverse effects on health and performance. However, the effects of natural ectoparasite levels on host physiology are less understood, with most research designs implementing experimental or hormonal manipulations of hosts. In this study, we examined the interplay between tick parasitism and host characteristics on body condition and locomotor performance in Eastern fence lizards in natural settings. We found a higher frequency of tick infections in male lizards relative to females, with larger males being more likely to experience tick infection. Infected lizards had reduced locomotor performance, max sprint speed and 2-m run speed. Together this suggests an energetic trade-off between increased immune function and reduced locomotor performance, which is consistent with the immunocompetence–handicap hypothesis. Higher numbers of ticks on adult male lizards may be explained by age as well as the immunosuppressive effects of testosterone. Tick infection did not appear to reduce overall body condition of lizard hosts. Our findings shed light on the interplay between ectoparasitic infection, host characteristics, and locomotor performance under natural conditions. Such insights are crucial for understanding host–parasite dynamics and determining the trade-offs for hosts within ecological contexts.