Intersexual sibling interactions and male benevolence in a fig wasp

We studied interactions between males and females of the Australian pollina ting fig wasp, Pleistodontes imperialis (Chalcidoidea, Agaonidae), in Ficus platypoda (Moraceae). As for many other fig wasps, all mating occurs withi n the confines of a syconium before females depart. We show that initially there is scramble competition between males for access to virgin females. D uring this time males excavated a small hole into a female's gall to mate t hrough. These holes were just large enough for insemination, but not large enough for females to exit their galls. Males ignored mated females, and as virgin females became scarce males switched strategies and began to enlarg e insemination holes until they were large enough for females to escape, sh owing that males enhance female fitness by means other than just mating. Sy conia with experimentally reduced numbers of males had fewer liberated fema les, suggesting that female fitness is strongly affected by the number of m ales present. Females may be unable to escape their galls unassisted becaus e of morphological adaptations to syconium founding. We argue that sex allo cation should be affected not only by competition among males but also by i ntersexual interactions between siblings. This could potentially offset the strong female bias predicted by local mate competition. (C) 2000 The Assoc iation for the Study of Animal Behaviour.