RESUMEN
Wild animals have parasites that can compromise their physiological and/or behavioural performance. Yet, the extent to which parasite load is related to intraspecific variation in performance traits within wild populations remains relatively unexplored. We used pumpkinseed sunfish (Lepomis gibbosus) and their endoparasites as a model system to explore the effects of infection load on host aerobic metabolism and escape performance. Metabolic traits (standard and maximum metabolic rates, aerobic scope) and fast-start escape responses following a simulated aerial attack by a predator (responsiveness, response latency and escape distance) were measured in fish from across a gradient of visible (i.e. trematodes causing black spot disease counted on fish surfaces) and non-visible (i.e. cestodes in fish abdominal cavity counted post-mortem) endoparasite infection. We found that a higher infection load of non-visible endoparasites was related to lower standard and maximum metabolic rates, but not aerobic scope in fish. Non-visible endoparasite infection load was also related to decreased responsiveness of the host to a simulated aerial attack. Visible endoparasites were not related to changes in metabolic traits or fast-start escape responses. Our results suggest that infection with parasites that are inconspicuous to researchers can result in intraspecific variation in physiological and behavioural performance in wild populations, highlighting the need to more explicitly acknowledge and account for the role played by natural infections in studies of wild animal performance.
Asunto(s)
Perciformes , Animales , Peces , Carga de Parásitos , Perciformes/fisiologíaRESUMEN
Fish inhabit environments that vary greatly in terms of predation intensity, and these predation regimes are generally expected to be a major driver of divergent natural selection. To test whether there is predator-driven intra-species variation in the locomotion, metabolism and water velocity preference of pale chub (Zacco platypus) along a river, we measured unsteady and steady swimming and water velocity preference among fish collected from both high- and low-predation habitats in the Wujiang River. We also measured the routine metabolic rate (RMR), maximum metabolic rate (MMR) and cost of transport (COT) and calculated the optimal swimming speed (Uopt). The fish from the high-predation populations showed a shorter response latency, elevated routine metabolism, lower swimming efficiency at low swimming speed and lower water velocity preference compared with those from the low-predation populations. Neither of the kinematic parameters fast-start and critical swimming speed (Ucrit) showed a significant difference between the high- and low-predation populations. The fish from the high-predation populations may improve their predator avoidance capacity primarily through an elevated routine metabolism and shorter response latency to achieve advanced warning and escape, rather than an improved fast-start swimming speed or acceleration. Thus, the cost of this strategy is an elevated RMR, and no trade-off between unsteady and steady swimming performance was observed in the pale chub population under various predation stresses. It was interesting to find that the high-predation fish showed an unexpected lower velocity preference, which might represent a compromise between predation avoidance, foraging and energy saving.