Size-dependent predation alters interactions between parasites and predators

Abstract

16Increasing evidence indicates that parasites play an important role within many systems as prey 17 for higher trophic levels. Predation on parasites can decrease their numbers and may affect host 18 infection rates. Cercariae, a free-living infectious stage of trematode parasites, are abundant in 19 freshwater systems and are directly consumed by a number of freshwater predators. However, 20 few studies have tested whether predators exhibit a preference for cercariae when alternative 21 prey are available or how these preferences vary across predator body sizes. We assessed 22 whether dragonfly larvae, top predators in freshwater systems without fish, foraged preferentially 23 when presented with two prey types, cercariae and zooplankton, and whether foraging 24 preferences changed across predator body size. Body size of larval dragonfly predators was 25 found to be significantly, and negatively, related to the fraction of cercariae in the diet. Larger 26 bodied dragonfly larvae shifted their diet choice from cercariae to zooplankton. Changes in 27 foraging selectivity as body size increases across a predator's ontogeny can alter the strength of 28 predator-prey interactions. Further investigation into size-selective foraging on parasites may 29 provide new insights into the effects of predation on parasite abundance and transmission in 30 natural systems.31 32

Consumer and host body size effects on the removal of trematode cercariae by ambient communities

“…Such alternative mechanisms of cercarial removal may explain the different findings in other aquatic predators where a negative relationship between predator body size and parasite removal due to prey size mismatches has been observed (e.g. damselfly nymphs, dragonfly larvae, mosquitofish; Orlofkse et al 2015;Catania et al 2016).…”

“…Such alternative mechanisms of cercarial removal may explain the different findings in other aquatic predators where a negative relationship between predator body size and parasite removal due to prey size mismatches has been observed (e.g. damselfly nymphs, dragonfly larvae, mosquitofish; Orlofkse et al ., 2015; Catania et al ., 2016). Our findings thus suggest that predator effects on cercarial removal rates may be more diverse and may also include mechanisms such as removal via mouth parts or gills similar to the filter feeding in bivalves and other filter feeders.…”

“…These comparisons show that brown shrimps have the ability to remove cercariae but only at higher shrimp densities. The absence of an effect of shrimp body size shown in this study may further suggest that cercarial removal may be independent of body size in shrimps in general, again differing from the expectation that there should be a size-dependent match-mismatch as observed in other cercarial predators (Orlofkse et al ., 2015; Catania et al ., 2016). Hence, the effect of predators on cercarial removal may be less predictable than in filter feeders and probably depends strongly on the mechanisms of cercarial removal in a respective predator.…”

“…Such a match-mismatch can also be expected to occur in the case of predation upon infective stages of parasites. Indeed, a negative relationship between predator body size and parasite removal has been observed in invertebrate predators (damselfly nymphs and dragonfly larvae) and vertebrate (juvenile vs. adult mosquitofish) of trematode cercarial stages in freshwater systems (Orlofkse et al ., 2015; Catania et al ., 2016). Further studies, also from different ecosystems, would be helpful to evaluate the generality of the effects of predator body size on parasite removal.…”

Cercarial behaviour alters the consumer functional response of three‐spined sticklebacks

“…While temperature may alter stickleback prey consumption (Wootton et al., 1980), the characteristic behavioural and physiological changes (reduced fright response, visible bulge and restricted stomach capacity) caused by severe S. solidus infections may also alter the foraging activity of this fish (Milinski, 1985; Tierney et al., 1993). Furthermore, parasite‐specific morphological and behavioural traits inherent to dispersal and transmission also alter its predation risk (Born‐Torrijos et al., 2020; Catania et al., 2016; Kaplan et al., 2009; Orlofske et al., 2015; Selbach et al., 2019).…”