Competition strategies and correlated selection on responses to polyandry in the seed beetle Callosobruchus maculatus

Polyandry reflected in multiple mating with different mates is regarded as favoured by natural selection in males but not necessarily in females, where conflicting effects on fitness components can occur. The present study aims to provide empirical evidence to predict which fitness components may be affected in this sexual conflict using a species that demonstrates potential between-population variation in their resolution: the cowpea weevil Callosobruchus maculatus. Two strains showing contrasting competition outcomes (scramble × contest) and contrasting life-history strategies based on trade-offs between longevity and fecundity are crossed for subsequent selection based on larval-competition strategy, expecting the production of a correlated response to multiple (polyandrous) mating. Such a response is expected because the scramble strain shows high fecundity (and lower longevity) and would benefit from multiple mating, in contrast with the contest strain, which shows high juvenile mortality. The scramble-selected lines would evolve a response of increased fecundity and reduced longevity under multiple and potentially polyandrous mating but the contest-selected lines would not respond to multiple (polyandrous) mating. Instead, both scramble- and contest-selected lines show increased fecundity and reduced longevity with multiple (polyandrous) matings, which did not affect egg weight. Indirect benefits of multiple (polyandrous) mating appear to be relevant for lines showing contest competition among juveniles.