Trait evolution under multiple selection pressures: Prey responses to predictable and unpredictable variation

Abstract

When a strong selection pressure, such as predation risk, varies widely in space and time, how should prey respond? When risk varies predictably, prey are hypothesized to respond in a risksensitive manner. It is less clear how prey should respond when risk varies unpredictably.Additionally, prey response may also depend on how predation risk interacts with other selection pressures. Our understanding of the complex action of multiple and variable selection pressures on prey traits is still comparatively poor. Here, we examine how predictable and unpredictable aspects of predation risk act together with another important selection pressure to influence prey behaviour in the rock pool breeding mosquito, Aedes vexans. Through the selection of sites for oviposition, female mosquitoes can influence the predation risk faced by their offspring. We tested how females select oviposition sites, when encountering pools that vary in larval predation risk and desiccation risk. We comprehensively quantified spatial and temporal variation in predation risk by measuring densities of predatory dragonfly nymphs in rock pools of different sizes, along the mosquito breeding season. We also measured hydroperiod length. We next conducted manipulative experiments in rock pools and measured female oviposition responses to variation in predation and desiccation risks. Predation risk varied widely in space and time. Desiccation risk only appeared important for the small pools. Ovipositing females appeared to respond to these multiple aspects of variation in selection pressures. Females seemed to respond to predictable variation by avoiding large pools that permanently harboured predators in natural settings. Female responses were more variable to medium-sized pools with naturally stochastic predator densities, highlighting the role of unpredictability in predation risk in shaping behaviour. Females did not clearly prefer small pools that were naturally devoid of predators but carried high desiccation risk, suggesting that they balance multiple risks -predation versus desiccation -when choosing oviposition sites. Our study suggests that wild populations may commonly experience multiple and variable selection pressures that can favour seemingly puzzling trait variation. We highlight the need to quantify variation in selection pressures and investigate how such variation, especially the unpredictable aspects, shapes 2 4 6

Social clues in risky pools: Perceived conspecific rivals strongly modify individual oviposition decisions in response to larval predation and competition

“…When background predation was low, social information promoted individuals to strongly reject pool networks; and when they do oviposit, to bet-hedge across the control and treatment pools. This is consistent with field patterns measuring oviposition behaviour of Aedes vexens with varying background predation risk broadly indicate that females consistently lay eggs in both predator present and predator-free pools across the season (Sharma and Isvaran 2019;Silberbush et al 2014). Interestingly, at a finer spatial scale, ovipositing solitary females preferentially deposited eggs in low predator pools despite the availability of a risk-free pool.…”

“…When faced with larval competition, females may avoid ovipositing in pools with conspecific broods to ensure more resources for their offspring (Munga et al 2006). In contrast, under larval predation, there is evidence of both avoidance (Blaustein et al 2004;Resetarits and Wilbur 1989) and preference for pools with predators across taxa (Sharma and Isvaran, 2019). Consequently, key life-history trade-offs may shift along these distinct selection gradients affecting fitness traits in both adults and offspring.…”