Adaptive growth reduction in response to fish kairomones allows mosquito larvae (Culex pipiens) to reduce predation risk

Abstract

Phenotypic plasticity is predicted to evolve when subsequent generations are likely to experience alternating selection pressures; e.g., piscine predation on mosquitoes (Culex pipiens) varies strongly depending on habitat type. A prey-choice experiment (exp. 1) detected a predilection of common mosquito predators (sticklebacks, Gasterosteus aculeatus) for large-bodied mosquito larvae, suggesting that larvae could benefit from suppressing growth under predation risk, and experiment 2 confirmed reduced pupa size and weight when we exposed larvae to stickleback kairomones. In experiment 3, we measured adult (imago) size instead to test if altered larval growthpatterns affect adult life-history traits. We further asked how specific life-history responses are, and thus, also used kairomones from introduced Eastern mosquitofish (Gambusia holbrooki), and from algivorous, non-native catfish (Ancistrus sp.). Adult body mass was equally reduced in all three kairomone treatments, suggesting that a non-specific anti-predator response (e.g., reduced activity) results in reduced food uptake. However, imagines were distinctly smaller only in the stickleback treatment, pointing towards a specific, adaptive life-history shift in response to the presence of a coevolved predator: mosquito larvae appear to suppress growth when exposed to their native predator, which presumably reduces predation risk, but also affects body size after pupation. Our study suggests that (1) not all antipredator responses are necessarily predator-specific, and (2) fluctuation in the cost-benefit ratio of suppressing larval growth has selected for phenotypic plasticity in C. pipiens larval life histories. This implies costs associated with suppressed growth, for example, in the form of lower lifetime reproductive success.

Context-dependent interactive effects of non-lethal predation on larvae impact adult longevity and body composition

“…As is true for most aquatic systems, these chemical cues originate either from injured prey or directly from the predator [ 57 – 60 ]. Effects of predation threat on larval growth and adult traits of mosquitoes have been infrequently examined [ 61 – 64 ]. Two-way interactions between nutrition availability, competition for resources and larval predation affect development and survival of mosquito larvae [ 61 , 65 ].…”

Elevated temperatures translate into reduced dispersal abilities in a natural population of an aquatic insect

“…On the other hand, delayed emergence is commonly explained by increased competition of insect larvae for limited resources (Agnew, Hide, Sidobre, & Michalakis, ; Gimnig et al, ; Livdahl, ). Earlier emergence often comes at a cost in terms of smaller adult body size, for example, in some species of mosquitoes (Beketov & Liess, ; Jourdan et al, ); congruently, T. maxima showed a reduced body size under higher conspecific densities. Furthermore, sex ratios affected wing length, suggesting an increased investment into dispersal abilities when males face strong mating competition.…”

Costly defense in a fluctuating environment—sensitivity of annual Nothobranchius fishes to predator kairomones

“…In many animal taxa, growth rate modulation in response to predatory cues appears to follow specific, efficient modes of predator avoidance. Small planktonic crustaceans and insects typically tend to decrease predator-encounter rate by slowing down growth (Dawidowicz & Wielanier, 2004;Gliwicz & Maszczyk, 2007;Pijanowska, Dawidowicz, Howe, & Weider, 2006), perhaps as a consequence of reduced foraging activity (Jourdan et al, 2016). In contrast, size reduction is less common in vertebrates (Barry, 2014;Smith, Burgett, Temple, & Sparks, 2016) as they can more easily escape predation by growing into a size refuge (e.g., through exceeding the predator's prey size range or through metamorphosis).…”