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Canopy Science |
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Fig Wasp Communities
Scientist: Simon Segar
Contact Email: s.t.segar@reading.ac.uk
Institution: University of Reading, Operation Wallacea, CAL
Project Description:
As keystone species fig trees (Moraceae: Ficus) are ubiquitous in tropical biomes, indeed they are the only plant genus to be consistently diverse in lowland rainforest on every tropical continent (Harrison, 2005). With over 750 species recorded (Berg and Corner, 2005) the genus is considered to be one of the largest and most morphologically diverse land plant genera on the planet. Even so, the importance of the genus is inordinate to its size with Ficus density often being the main factor in vertebrate distribution (e.g. Kinnaird et al., 1996). Fig fruit (technically enclosed inflorescences, referred to as syconia) are pollinated by short-lived species-specific wasps (Aagonidae), which can fly tens of kilometres across the canopy to home in on volatiles emitted by receptive figs (Nason et al., 1998). On arrival they crawl into figs through a bract lined passage (often losing wings and antennae on the way) in order to pollinate or lay eggs in the ovules within the syconia before dying. Pollinating wasps and fig trees form an obligate mutualism (Weiblen, 2002) and the wasps are the only organisms capable of delivering pollen to the figs, in turn the wasps cannot develop in anything other than the appropriate fig host. In reality fig trees can be pollinated by more than one species of pollinator and in some cases pollinators can pollinate multiple fig species (Machado et al., 2005). The manner in which pollinators and fig trees have co-evolved is an active field of research, but the detailed studies carried out in South America (Marusich and Machado, 2007) have yet to be replicated in SE Asia.
In addition to pollinating wasps syconia are utilised by several sub-families of non-pollinating fig-wasps (NPFWs) which have a diversity of life histories: some have evolved convergently with the pollinators to enter the fig, others use long ovipositors to inject eggs through the fig wall into ovules (gallers) or into the eggs of other fig wasps (parasitoids) others even lay eggs into the developing parasitoids (hyper-parasitoids)! In all five independently colonising sub-families of NPFW attack Ficus and local radiations of these sub-families have invaded local radiations of Ficus to form comparative communities. Fig wasp communities can contain up to 30 species (Compton and Hawkins, 1992) and provide an excellent opportunity to study how communities have evolve; do these communities share a common end-point despite differing in starting taxa and global location?
An important prerequisite of this type of question is to know how the different sub-families have radiated across their Ficus hosts in terms of biogeography and phylogenetics. It is also a great opportunity to study the strength of co-evolution between different guilds of organisms associated with the same host plant genus (Silveus et al., 2008). As such I am interested in the molecular phylogenetics of the Sycorictinae, a sub-family (thought to be mostly parasitoids or inquilines) of NPFW ubiquitous in SE Asian fig wasp communities. At one end of the taxonomic scale I am creating a molecular phylogeny of the Australasian representatives of this sub-family (including some of it’s putative sister lineages in the family Pteromalidae) in order to compare this to the Ficus phylogeny: how has this group radiated across Ficus? At a more detailed level I am investigating the host specificity of individual Sycoryctinae species and how speciation proceeds in this group, how often are new species the result of strict sense co-speciation, host switches or ecological speciation on the same host (Cook and Segar, in press)?
I have been lucky enough to work on figs and fig wasps in Northern Australia (with Imperial College London and the University of Reading) and Southern Sulawesi (with Operation Wallacea).
References
Berg, C.C. & Corner, E.J.H. (2005) Moraceae - Ficus. Flora Malesiana, Ser. I, 17/2, Leiden., 289-301.
Compton, S.G. & Hawkins, B.A. (1992) Determinants of Species Richness in Southern African Fig Wasp Assemblages. Oecologia, 91, 68-74.
Harrison, R.D. (2005) Figs and the diversity of tropical rainforests. Bioscience, 55, 1053-1064.
Kinnaird, M. F., O’Brien, T. G., Suryadi, S. (1996). Population Fluctuation in Sulawesi Red Knobbed Hornbills: Tracking Figs in Space and Time. The Auk, 133, 431-440.
Machado, C.A., Robbins, N., Gilbert, M.T.P., & Herre, E.A. (2005) Critical review of host specificity and its coevolutionary implications in the fig/fig-wasp mutualism. Proceedings of the National Academy of Sciences of the United States of America, 102, 6558-6565.
Marussich, W.A. & Machado, C.A. (2007) Host-specificity and coevolution among pollinating and nonpollinating New World fig wasps. Molecular Ecology, 16, 1925-1946.
Nason, J. D., Herre, E. A. & Hamrick, J. L. 1998 The breeding structure
of a tropical keystone plant resource. Nature 391, 685–687.
Silvieus, S.I., Clement, W.L., & Weiblen., G.D., eds. (2008) Cophylogeny of fig pollinators and parasitoids, pp 14. University of California Press, Berkeley, California.
Weiblen, G.D. (2002) How to be a fig wasp. Annual Review of Entomology, 47, 299-330.
Publications
Cook, J.M. and Segar, S.T. Speciation in fig wasps. Ecological Entomology. In Press.
Dunn, D.W., Segar, S.T., Ridley, J., Chan, R., Crozier, R.H., Yu, D.W. & Cook, J.M. (2008) A Role for Parasites in Stabilising the Fig-Pollinator Mutualism. PLoS Biology, 6, 490-496.
Participants:
Simon Segar, Professor James Cook, Vicki Tough, Operation Wallacea
Project Location: UK, Northern Australia, Southern Sulawesi
Added Date: 21-Oct-2009
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