Speciation in fig wasps

Abstract

1. There are over 700 species of fig trees in the tropics and several thousand species of fig wasps are associated with their syconia (inflorescences). These wasps comprise a monophyletic family of fig pollinators and several diverse lineages of non‐pollinating wasps. The pollinator larvae gall fig flowers, while larvae of non‐pollinating species either initiate their own galls or parasitise the galls of other wasps.2. A single fig species has one to four pollinator species and also hosts up to 30 non‐pollinating wasp species. Most wasps show a high degree of host‐plant specificity and are known from only a single fig species. However, in some cases wasps may be shared across closely related fig species.3. There is impressive morphological co‐evolution between figs and fig wasps and this, combined with a high degree of partner specificity, led to the expectation that figs and pollinators have cospeciated extensively. Comparison of deep phylogenies supports long‐term codivergence of figs and pollinators, but also suggests that some host shifts have occurred.4. Phylogenies of more closely related species do not match perfectly and may even be incongruent, suggesting significant roles for processes other than strict cospeciation. Combined with recent evidence on host specificity patterns, this suggests that pollinator wasps may often speciate by host shifts between closely related figs, or by duplication (the wasp speciates but the fig doesn't). The frequencies and biological details of these different modes of speciation invite further study.5. Far less is known about speciation in non‐pollinating fig wasps. Some lineages have probably co‐evolved with figs and pollinators for most of the evolutionary history of the symbiosis, while others appear to be more recent colonisers. Many species appear to be highly host‐plant specific, but those that lay eggs through the fig wall without entering the syconium (the majority of species) may be subject to fewer constraints on host shifting than pollinators. There is evidence for substantial host shifting in at least one genus, but also evidence for ecological speciation on the same host plant by niche shifts in other cases.6. Finally, recent work has begun to address the issue of ‘community phylogeny’ and provided evidence for long‐term co‐divergence of multiple pollinating and non‐pollinating wasp lineages with their host figs.