Immune deployment increases larval vulnerability to predators and inhibits adult life‐history traits in a dragonfly

Abstract

While deploying immune defences early in ontogeny can trade-off with the production and maintenance of other important traits across the entire life cycle, it remains largely unexplored how features of the environment shape the magnitude or presence of these lifetime costs. Greater predation risk during the juvenile stage may particularly influence such costs by (1) magnifying the survival costs that arise from any handicap of juvenile avoidance traits and/or (2) intensifying allocation trade-offs with important adult traits. Here, we tested for predator-dependent costs of immune deployment within and across life stages using the dragonfly, Pachydiplax longipennis. We first examined how larval immune deployment affected two traits associated with larval vulnerability to predators: escape distance and foraging under predation risk. Larvae that were induced to mount an immune response had shorter escape distances but lower foraging activity in the presence of predator cues. We also induced immune responses in larvae and reared them through emergence in mesocosms that differed in the presence of large predatory dragonfly larvae (Aeshnidae spp.). Immune-challenged larvae had later emergence overall and lower survival in pools with predators. Immune-challenged males were also smaller at emergence and developed less sexually selected melanin wing coloration, but these effects were independent of predator treatment. Overall, these results highlight how mounting an immune defence early in ontogeny can have substantial ecological and physiological costs that manifest both within and across life stages.

Effects of hydroperiod on growth, development, survival and immune defences in a temperate amphibian

“…Developmental stressors such as predation (e.g. in dragonflies: Moore, Lis, & Martin, 2018), high densities of conspecifics (e.g. in frogs: Echaubard, Little, Pauli, Lesbarrè Res, & Lesbarrères, 2010), a shortened hydroperiod (e.g.…”

Temperature shapes the costs, benefits and geographic diversification of sexual coloration in a dragonfly

“…For instance, defending against infection inhibits wing colour production in odonates (Siva‐Jothy ; Moore et al . ). The observed geographic pattern could then plausibly reflect variation in parasite load.…”

“…As males can also produce wing coloration in this region of the wing prior to maturation (Moore & Martin ; Moore et al . ), we positively scored males that were not mature but exhibited such coloration ( c . 2% of all observations).…”

Warm developmental temperatures induce non‐adaptive plasticity in the intrasexually selected colouration of a dragonfly

“…Briefly, in the cooler portions of the species' range (i.e. northern and eastern), male P. longipennis produce dark intrasexually selected wing melanisation (Paulson, ; Moore & Martin, ; Moore et al ., ). In addition to signalling a male's condition and fighting ability to rivals (Moore & Martin, ), recent work in a wild population showed that having more of this wing colouration improves a male's heating ability and, subsequently, its territorial success under cooler conditions (Moore et al ., ).…”

“…Because of these thermal properties, males that facultatively develop more colouration under cooler conditions should gain a fitness advantage, all else being equal. Conversely, because colouration is energetically costly to produce and maintain (Moore & Martin, , ; Moore et al ., ), developing more colouration under warmer conditions should provide smaller net benefits or may even impose costs associated with overheating (Moore et al ., ). Indeed, males have substantially reduced pigmentation in the warmest regions (Paulson, ; Moore et al ., ).…”