BackgroundSymbiotic relationships have contributed to major evolutionary innovations, the maintenance of fundamental ecosystem functions, and the generation and maintenance of biodiversity. However, the exact nature of host/symbiont associations, which has important consequences for their dynamics, is often poorly known due to limited understanding of symbiont taxonomy and species diversity. Among classical symbioses, figs and their pollinating wasps constitute a highly diverse keystone resource in tropical forest and savannah environments. Historically, they were considered to exemplify extreme reciprocal partner specificity (one-to-one host-symbiont species relationships), but recent work has revealed several more complex cases. However, there is a striking lack of studies with the specific aims of assessing symbiont diversity and how this varies across the geographic range of the host.ResultsHere, we use molecular methods to investigate cryptic diversity in the pollinating wasps of a widespread Australian fig species. Standard barcoding genes and methods were not conclusive, but incorporation of phylogenetic analyses and a recently developed nuclear barcoding gene (ITS2), gave strong support for five pollinator species. Each pollinator species was most common in a different geographic region, emphasising the importance of wide geographic sampling to uncover diversity, and the scope for divergence in coevolutionary trajectories across the host plant range. In addition, most regions had multiple coexisting pollinators, raising the question of how they coexist in apparently similar or identical resource niches.ConclusionOur study offers a striking example of extreme deviation from reciprocal partner specificity over the full geographical range of a fig-wasp system. It also suggests that superficially identical species may be able to co-exist in a mutualistic setting albeit at different frequencies in relation to their fig host’s range. We show that comprehensive sampling and molecular taxonomic techniques may be required to uncover the true structure of cryptic biodiversity underpinning intimate ecological interactions.Electronic supplementary materialThe online version of this article (doi:10.1186/s12862-014-0189-9) contains supplementary material, which is available to authorized users.

Mutualisms involve cooperation between species and underpin several ecosystem functions. However, there is also conflict between mutualists, because their interests are not perfectly aligned. In addition, most mutualisms are exploited by parasites. Here, we study the interplay between cooperation, conflict and parasitism in the mutualism between fig trees and their pollinator wasps. Conflict occurs because each fig ovary can nurture either one seed or one pollinator offspring and, while fig trees benefit directly from seeds and pollinator offspring (pollen vectors), pollinators only benefit directly from pollinator offspring. The mechanism(s) of conflict resolution is debated, but must explain the widespread observation that pollinators develop in inner, and seeds in outer, layers of fig flowers. We recently suggested a role for non‐pollinating figs wasps (NPFWs) that are natural enemies or competitors of the pollinators and lay their eggs through the fig wall. Most NPFW offspring develop in outer and middle layer flowers, suggesting that inner flowers provide enemy‐free space for pollinator offspring. Here, we test the hypothesis that NPFWs cannot reach inner flowers, by measuring wasp and fig morphology at the species‐specific times of NPFW attack in the field. We found that three species of Sycoscapter and Philotrypesis wasps that parasitise pollinators could reach 34–73%, 75–92% and 82–97% of fig ovaries, respectively. Meanwhile, Eukobelea and Pseudidarnes gall‐formers, despite having shorter ovipositors, can access almost all fig flowers (93–99% and 100%), because they attack smaller (younger) fig fruits. Our mechanistic results from ovipositing wasps support spatial patterns of wasp offspring segregation within figs to suggest that inner ovules provide enemy‐free‐space for pollinators. This may contribute to mutualism stability by helping select for pollinators to avoid laying eggs where they are likely to be parasitised. These outer flowers then remain free to develop as seeds, promoting mutualism persistence.

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Fig trees (Ficus spp.) are pollinated by tiny wasps that enter their enclosed inflorescences (syconia). The wasp larvae also consume some fig ovules, which negatively affects seed production. Within syconia, pollinator larvae mature mostly in the inner ovules whereas seeds develop mostly in outer ovules-a stratification pattern that enables mutualism persistence. Pollinators may prefer inner ovules because they provide enemy-free space from externally ovipositing parasitic wasps. In some Australasian Ficus, this results in spatial segregation of pollinator and parasite offspring within syconia, with parasites occurring in shorter ovules than pollinators. Australian figs lack non-pollinating fig wasps (NPFW) that enter syconia to oviposit, but these occur in Africa and Asia, and may affect mutualist reproduction via parasitism or seed predation. We studied the African fig, F. burkei, and found a similar general spatial pattern of pollinators and NPFWs within syconia as in Australasian figs. However, larvae of the NPFW Philocaenus barbarus, which enters syconia, occurred in inner ovules. Philocaenus barbarus reduced pollinator abundance but not seed production, because its larvae replaced pollinators in their favoured inner ovules. Our data support a widespread role for NPFWs in contributing to factors preventing host overexploitation in fig-pollinator mutualisms.

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