Mortal combat and competition for oviposition sites in female pollinating fig wasps

Abstract

Aggressive contests between animals are common but rarely result in death because the benefits of winning a fight rarely exceed the cost of losing. Lethal combat can evolve, however, when the contested resource translates to much of the future reproductive success of each combatant. Female agaonid fig wasps pollinate and lay their eggs in the flowers within the enclosed inflorescences (“figs”) of fig trees (Ficus spp.). Wasps rarely leave the first fig entered so the reproductive success of each “foundress” usually depends on the availability of flowers within a single fig. We report for the first time lethal combat between female agaonids, in the undescribed Pegoscapus sp. that pollinates Ficus citrifolia in southeastern Brazil. In staged dyadic contests, wasps showed no aggression outside or inside the fig until one foundress oviposited. The first wasp to oviposit then became aggressive, which usually resulted in the death of its competitor. Examination of dead foundresses in naturally occurring figs showed that injuring competitors, particularly through decapitation, was effective at reducing their oviposition rates. In a Panamanian F. citrifolia population, pollinated by another wasp species, Pegoscapus tonduzi , there was little aggression between foundresses in similar contests. We suggest that reduced aggression in P. tonduzi reflects less competition for resources essential for successful reproduction due to on average fewer foundresses per flower in Panama.