Host life history and host–parasite syntopy predict behavioural resistance and tolerance of parasites

Abstract

Summary1. There is growing interest in the role that life-history traits of hosts, such as their 'pace-oflife', play in the evolution of resistance and tolerance to parasites. 2. Theory suggests that, relative to host species that have high syntopy (local spatial and temporal overlap) with parasites, host species with low syntopy should have lower selection pressures for more constitutive (always present) and costly defences, such as tolerance, and greater reliance on more inducible and cheaper defences, such as behaviour. Consequently, we postulated that the degree of host-parasite syntopy, which is negatively correlated with host pace-of-life (an axis reflecting the developmental rate of tadpoles and the inverse of their size at metamorphosis) in our tadpole-parasitic cercarial (trematode) system, would be a negative and positive predictor of behavioural resistance and tolerance, respectively. 3. To test these hypotheses, we exposed seven tadpole species to a range of parasite (cercarial) doses crossed with anaesthesia treatments that controlled for anti-parasite behaviour. We quantified host behaviour, successful and unsuccessful infections, and each species' reaction norm for behavioural resistance and tolerance, defined as the slope between cercarial exposure (or attempted infections) and anti-cercarial behaviours and mass change, respectively. Hence, tolerance is capturing any cost of parasite exposure. 4. As hypothesized, tadpole pace-of-life was a significant positive predictor of behavioural resistance and negative predictor of tolerance, a result that is consistent with a trade-off between behavioural resistance and tolerance across species that warrants further investigation. Moreover, these results were robust to considerations of phylogeny, all possible reorderings of the three fastest or slowest paced species, and various measurements of tolerance. 5. These results suggest that host pace-of-life and host-parasite syntopy are powerful drivers of both the strength and type of host defence strategies against parasites. Future research should evaluate how often and how strongly host pace-of-life and host-parasite syntopy are correlated and which is the better predictor of the strength and type of host investments in anti-parasite defences.

Predator diversity, intraguild predation, and indirect effects drive parasite transmission

“…Finally, whereas we identified a general trait of predatorswhere they fall on an IG predation continuum-that predicts their ability to reduce disease and possibly pests in general, recent studies suggest that there might also be general traits of host species that predict their ability to dilute or amplify disease risk (46,47) and herbivory (48). Consequently, to enhance infectious disease management and biocontrol we encourage further work that searches for traits of host and nonhost species that might be useful indicators of species that can increase or decrease parasite and pest populations.…”

Vertebrate defense against parasites: Interactions between avoidance, resistance, and tolerance

“…Detecting the threat of infection and avoiding or minimizing parasite exposure generally represents the first line of host defense. However, very few empirical studies have compared avoidance behavior among species and populations (but see Sears et al., ; Tranter, LeFevre, Evison, & Hughes, ), which is why our understanding of the magnitude of underlying genetic variation is limited. Here, trout clearly avoided areas containing parasites and this pattern was similar in the two genetically distinct populations.…”

Combined Effects of Pesticides and Trematode Infections on Hourglass Tree Frog Polypedates cruciger

“…If this mortality is representative of what occurs in the wild, then A. burminis and at least three of these pesticides have the potential to contribute to amphibian population declines. Given that many amphibians are likely exposed to A. burminis and these chemicals, cross-species studies would be valuable to better understand which amphibian species are at greatest risk (e.g., Sears et al 2015). …”