Larval body condition regulates predator‐induced life‐history variation in a dragonfly

Abstract

Abstract. Organisms with complex life cycles commonly exhibit adaptive plasticity in the timing of transitions between life stages. While the threat of predation is predicted to induce earlier transitions, empirical support has been equivocal. When predation risk affects both the propensity to transition to the next life stage and the ability to reach the energetic thresholds necessary to complete the transition, only those individuals in the best physiological condition may be able to accelerate development and emerge earlier. To test this hypothesis, we followed uniquely marked dragonfly larvae (Pachydiplax longipennis) through emergence in pools where we factorially manipulated the presence of a large heterospecific predator (Anax junius) and cannibalism risk via conspecific size variation. Consistent with our hypothesis, high-condition larvae were more likely to emerge in the presence of the heterospecific predator than in its absence, and low-condition larvae were more likely to emerge in its absence than in its presence. Moreover, high-condition larvae emerged earlier when cannibalism risk was high than when it was low. Predation risk therefore has condition-dependent effects on emergence. As predation risk frequently affects resource accumulation, similar mechanisms across taxa could commonly underlie the incongruence between empirical results and theoretical expectations for predator-induced life-history variation.

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

“…Contrary to our predictions, nonlethal effects of predation risk did not intensify the costs of immune deployment to adult traits. Despite strong theoretical predictions, predation risk frequently has equivocal effects on life‐history traits in organisms with complex life cycles (reviewed in Benard, ; Relyea, ), perhaps because behavioural modifications offset any effects (McPeek et al ., ; Touchon et al ., ; Moore et al ., ), or because trade‐offs occur with traits experiencing more diffuse selective pressures than life‐history traits (e.g. oxidative stress, Slos et al ., ; digestive physiology, Stoks et al ., ).…”

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

“…In late spring, individuals move towards the margins of their natal pond to complete the larval stage (Wissinger, ; McCauley et al ., ). Individuals emerge between mid‐June and early July (Moore et al ., ), reaching full reproductive maturity less than 2 weeks later (Corbet, ). Males typically begin defending territories between late June and mid July, and then live for another 2 weeks or more (Moore & Martin, ).…”

On the evolution of carry‐over effects

“…Many carry‐over effects occur when the environment influences the expression of traits in an earlier life stage, and those trait values are directly carried over into subsequent life stages. We term these ‘direct carry‐over effects’; and examples include size at metamorphosis in marine invertebrates, aquatic insects and amphibians (Allen & Marshall, ; Boes & Benard, ; Moore, Lis, & Martin, ). Another type of carry‐over effect arises when the environment of an earlier life stage affects a trait's expression in the later life stage, but does not affect the expression of that same trait in the earlier life stage.…”