Females use multiple cues to assess competition for egg-laying decisions

Abstract

Animals deploy a wide suite of behavioural responses to reduce fitness costs related to competition. One common strategy is spatial avoidance of resource patches associated with high competition and this involves a need to accurately assess the level of competition associated with patches. Although well-studied in the context of predation risk (alarm cues vs kairomones), we lack in our understanding of how inputs from multiple types of cues are used for assessing the level of conspecific competition. We tested how Aedes aegypti females select sites for oviposition when they encounter multiple types of cues from varying densities of conspecifics. We hypothesised that females perceive conspecific young within these sites as potential competition for their offspring, and tailor their response to the type and level of competition. Through binary choice trials, we assessed female oviposition behaviour in response to a gradient in two types of conspecific cues - egg and larvae. Our results indicate that female response was sensitive to the type of cue. Females showed attraction towards pools with low densities of both egg and larval conspecifics indicating conspecific cueing and the strength of response was stronger towards egg cues. However, this attraction response disappeared at high densities of conspecifics (both egg and larvae) suggesting that the resulting trade-off between benefits from conspecific cueing and costs of competition likely shapes oviposition site selection responses. The broad nature of the oviposition response was similar toward both egg and larval cues, but there were fine level differences in responses towards egg and larvae that depended on the conspecific density level. Our study shows that animals are under selection to use multiple cues to assess conspecific competition to minimise the costs of competition.