Flight-fecundity tradeoffs in wing-monomorphic insects

Winged insects often spend considerable amounts of energy in flight, searching for food, escaping predators, and dispersing. In females, flight is hypothesized to reduce resources available for egg production, thus leading to a tradeoff between flight and fecundity. Yet, the generality of a flight-fecundity tradeoff in insects may have been overestimated, given that empirical validation of such a tradeoff has largely relied on studies in wing-polymorphic insects. In this review, we evaluate evidence of a flight-fecundity tradeoff in wing-monomorphic insects by conducting a systematic literature search. We compiled information from studies on migratory and non-migratory insects, testing for an association between flight and fecundity and using a number of different methods—phenotypic and genotypic correlations, manipulation of resource availability, and manipulation of either flight or fecundity. Although most studies indicated a negative association between flight and fecundity in wing-monomorphic insects, evidence for a tradeoff between the two traits was less prevalent. In several contexts, there were species that showed none or a positive association between both traits. Importantly, flight and fecundity in wing-monomorphic insects was related in a number of ways: via physiological constraints—resource-based tradeoffs—as well as via biomechanical constraints—when egg loads affected take-off performance—, due to adaptive negative correlations—when switching from flight to egg production if appropriate conditions to reproduce were encountered—and, due to adaptive positive correlations—when optimal flight and high fecundity were favoured for colonizing new habitats.