Predation risk increases immune response in a larval dragonfly (Leucorrhinia intacta)

Abstract

Predators often negatively affect prey performance through indirect, non-consumptive effects. We investigated the potential relationship between predator-induced stress and prey immune response. To test this, we administered a synthetic immune challenge into dragonfly larvae (Leucorrhinia intacta) and assessed a key immune response (level of encapsulation) in the presence and absence of a caged predator (Anax junius) at two temperatures (22 degrees C and 26 degrees C). We hypothesized that immune response would be lowered when predators were present due to lowered allocation of resources to immune function and leading to reduced encapsulation of the synthetic immune challenge. Contrary to our expectations, larvae exposed to caged predators had encapsulated monofilaments significantly more than larvae not exposed to caged predators. Levels of encapsulation did not differ across temperatures, nor interact with predator exposure. Our results suggest that the previously observed increase in mortality of L. intacta exposed to caged predators is not driven by immune suppression. In situations of increased predation risk, the exposure to predator cues may induce higher levels of melanin production, which could lead to physiological damage and high energetic costs. However, the costs and risks of increased allocations to immune responses and interactions with predation stress remain unknown.

Exposure to potentially cannibalistic conspecifics induces an increased immune response

“…S2). These results, in conjunction with previous work (Duong and McCauley, ; Van Allen et al ., ), suggest that, similar to predators, potentially cannibalistic conspecifics may have indirect beneficial effects on their potential prey by decreasing their risk of future pathogen infections (Moret and Siva‐Jothy, ) via immune enhancement. Alternatively, individuals exposed to potential cannibals that induce an immune priming response could be disadvantaged if the priming is costly and reduces the resources available for other life history challenges (e.g.…”

“…Although it is not possible to make direct comparisons across experiments, qualitatively, the effect of conspecifics appears to be similar to the effect of top predators on the melanisation response; Duong and McCauley (2016) showed that the threat of predation positively correlated with an increased immune response in L. intacta larvae (comparing our Figs 1 and 2 with the results from Duong and McCauley (2016). Previous studies have shown that tadpole prey show stronger behavioural and physiological plasticity in response to kairomones and alarm cues associated with a dragonfly predator consuming conspecifics compared with experimentally crushed conspecifics (Schoeppner and Relyea, 2005) or the presence of a predator (Schoeppner and Relyea, 2009).…”

“…Predator‐induced physiological plasticity can take many forms, depending on the interactions between stress responses and immune function (Adamo, ,b). Recent evidence has shown that exposure to predator cues can induce heightened immune responses by prey in some contexts (Duong and McCauley, ; Adamo et al ., ), possibly as a response to the increased risk of wounding by predators (Dhabhar, ). However, predator exposure can also be immunosuppressive (Adamo et al ., ).…”

Predator stress-induced immunosuppression: trade-off, immune redistribution or immune reconfiguration?

“…haemocyte number, Joop and Rolff, 2004;phenoloxidase activity, Slos et al, 2009; melanization of implants, Duong and McCauley, 2016), with one study (Op de Beeck et al, 2016) finding a negative effect of predator cues on phenoloxidase activity in mosquito larvae (when measured on the whole animal, as opposed to haemolymph levels). The effect on inducible mechanisms (e.g.…”

“…Such a perspective may help make sense of the mix of increased and decreased immune functions found in larval insects exposed to chronic predator stress (e.g. Joop and Rolff, 2004;Slos et al, 2009;Duong and McCauley, 2016;Op de Beeck et al, 2016).…”