Kairomone-induced changes in mosquito life history: effects across a food gradient

The aquatic immature stages of species with complex life histories exhibit a range of defense mechanisms in response to predator released kairomones (PRK). Employing these costly mechanisms often results in delayed metamorphosis. Larvae of the house mosquito Culex pipiens (Linnaeus) show a rare exception of accelerated metamorphosis in response to kairomones originated from the mosquitofish Gambusia affinis (Baird and Girard). In a series of lab experiments we examined whether this response is context-dependent with respect to food availability (i.e. applied only when food is abundant and cost is low). We examined life history variables of C. pipiens larvae, reared at different levels of food availability, either with or without PRK. We further examined the effect of PRK on the foraging behavior of the larvae at different instars. We also examined the effect of PRK-induced behavior on larvae survival under actual predation. We showed that the response of C. pipiens larvae to PRK was independent of food availability. Larvae exposed to PRK were less active and survived longer when exposed to direct predation. Exposure to both PRK and small food amounts also resulted in reduced adult size and survival period. The effects of food and PRK were independent of one another. We argue that for organisms with short development time, such as mosquitoes, decreasing time to metamorphosis may be the main feasible refuge from increased predation risk. Hence, Culex larvae exploit their capability for rapid development rate as a main anti-predator mechanism, minimizing the time spent in high-risk environments by accelerating metamorphosis, regardless of available resources, at the expense of other life history traits.