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The Nonpollinating Wasp Fauna of Ficus pertusa: Exploitation of a Mutualism?
Judith L. Bronstein
Vol. 61, No. 2 (Jun., 1991), pp. 175-186
Stable URL: http://www.jstor.org/stable/3545335
Page Count: 12
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Figs (Ficus spp.) are well known for their species-specific interactions with pollinating wasps (Hymenoptera: Chalcidoidea: Agaonidae). Many other highly specific but nonpollinating species develop within fig inflorescences (syconia) as well. Like the majority of species that exploit coevolved mutualisms, most aspects of their biology are virtually unknown. Here, I report on the three undescribed wasp species (Chalcidoidea: Torymidae: Sycophaginae) commonly associated with a neotropical fig (Ficus pertusa), focusing on their dependence on the mutualism between F. pertusa and its pollinator Pegoscapus silvestrii, and their impact upon it. Depending on the feeding habits of larval nonpollinators, their presence within syconia may or may not be costly to figs and pollinators. Indirect evidence suggests that the species exploiting F. pertusa feed on nourishing tissue that they induce within fig ovaries that are unexploited by the pollinators, rather than on developing pollinators or seeds. Thus, in this case any costs to the mutualists should be indirect and probably small. In this study, they were so small as to be unmeasurable. The ubiquity of nonpollinators in figs and the lack of effective defenses against them may be due in part to this weak impact on their hosts. F. pertusa's three torymid species are highly dependent on the fig/pollinator interaction at two stages. First, they can only reproduce if females have oviposited within pollinated syconia, since trees abscise nearly all unpollinated ones early in development. Torymid oviposition was in fact delayed relative to pollination, and in the one species investigated, females discriminated among syconia and chose to oviposit in the pollinated ones. Second, the torymids' offspring depend on the pollinators' male offspring to create an escape passage out of the mature syconium. Possibly for this reason, maturation times of all wasp species within the syconium are highly synchronized. Many traits involved in this dependence on the fig/pollinator mutualism are similar among torymids inhabiting the same fig species. These traits appear to represent convergent evolution among diverse, unrelated torymid species rather than similarity by descent. Nonpollinator species that depend on the fig/pollinator interaction at these stages are those most likely to be associated with a single fig/pollinator pair, since synchronization with the obligate pollinator's life cycle is most critical for them.
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