Sex-specific responses of pollinating and non-pollinating wasps to host resource availability in a fig tree–fig wasp mutualism

In some mutualisms, system stability is facilitated by hosts preferentially allocating resources to tissue supporting beneficial symbionts, which can increase costs to ‘cheater’ symbionts and parasites that fail to benefit hosts. However, sex-specific responses by symbionts and parasite species, especially those exhibiting pronounced sexual dimorphism, remain unexamined. We used Ficus racemosa to test how pollen presence and foundress numbers affect offspring production and body sizes in the pollinator symbiont Ceratosolen fusciceps and a non-pollinating parasite Sycophaga fusca. In both wasp species, pollen absence and increased foundress numbers led to declines in offspring production that were most pronounced in females but this was only apparent at high foundress density in S. fusca. Pollen absence and increased foundress numbers also resulted in body size reductions, especially in females. We suggest these patterns reflect greater resource demands of the larger females and also interspecific differences that may partially reside in male S. fusca possessing large mandibles used in intra-sexual combat. Furthermore, interspecific differences in reproductive biology may result in S. fusca foundresses assessing host fig quality for offspring sex allocation. Future investigations should consider a complex interplay between factors affecting sex allocation strategies and offspring mortality where both species coexist.