Mapping the fig wasp across three continents

 

Fig wasps hatching

Fig wasps hatching

A detailed picture of the biogeography and diversification of a key fig wasp subfamily is the result of research spanning three continents (Africa, Australasia and South America). A combination of molecular phylogenetics and ecology was used to investigate the wasp’s converging community structure.

Representatives of the large (>750 species) pan-tropical terrestrial plant genus Ficus (Moraceae) are ubiquitous in tropical forests, where they produce ‘fruit’ (actually enclosed inflorescences known as syconia) all year round. They are therefore considered to be ‘key stone’ species as they help maintain vertebrate frugivore populations whilst other fruit are scarce.

There is a conflict between mutualists as selection should favour wasps that exploit as many fig flowers as possible at the expense of seeds

This continual production is necessary to support populations of their tiny, often species specific, pollinating wasps (Chalcidoidea: Agaonidae). These two partners form an obligate pollination mutualism. Female wasps enter a single syconium (and in most cases never leave) to pollinate and lay their eggs; within the syconium single female flowers develop as either a seed or a wasp, but not both. Once developed the female pollinating fig wasps collect pollen before dispersing up to tens of kilometres to a receptive tree.

Conflict

There is a conflict between mutualists as selection should favour wasps that exploit as many fig flowers as possible at the expense of seeds. This clearly does not happen as seeds are nearly always produced.

Figs and fig wasps have thus become a model system for studying the resolution of conflict between mutualists. A diverse range of other topics has also been addressed using this system, from sex allocation to speciation and the co-existence of cryptic species.

Non-pollinating fig wasps

Ants on figs

Figs and fig wasps have become a model system for studying the resolution of conflict between mutualists

Furthermore, a host of distantly related chalcid wasps referred to as the non-pollinating fig wasps (NPFW) also utilise fig syconia. Some develop at the cost of seeds or other fig tissue, whilst others lay their eggs in flowers containing other wasps. These wasps can form complex and diverse communities of up to 30 species.

We are interested in how such biodiversity has been generated. As each continent has its own long isolated endemic radiation of Ficus lineage (section) there is potential for studying how communities are assembled over evolutionary time.

Our recent research in Indonesia and Australia has focused on elucidating the impact of different NPFW lineages on fig reproductive output. We have also been investigating mechanisms stabilising the fig/pollinator interaction (including the role of NPFWs).

Written by

  • , School of Biological Sciences, University of Reading
  • , School of Biological Sciences, University of Reading
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