Overview

Brief Summary

The chalcidoid wasp family Agaonidae includes nearly four hundred described species, all of which have intimate mutualistic relationships with Ficus figs (of which there are around 800 described species). As now commonly defined (i.e., excluding the non-pollinating fig wasps; Rasplus et al. 1998; Munro et al. 2011), the family Agaonidae is monophyletic (i.e., the group is descended from a single common ancestor and includes all lineages descended from that ancestor). Both figs and fig-pollinating wasps occur mainly in tropical and subtropical areas of the southern hemisphere. Fig wasp diversity varies geographically, with the Asian and Australasian regions harboring the highest species richness. Figs and their wasp pollinators provide extraordinary opportunities to investigate fundamental questions in evolution and ecology relating to coevolution, speciation, and the evolution and maintenance of mutualisms. Both the figs and their pollinating wasps are completely dependent on each other for survival and reproduction: figs can only be pollinated by fig wasps and fig wasps can only reproduce within figs. (Most commercial figs are parthenocarpic, requiring no fertilization, and hence no pollination at all, to produce fruit, and this phenomenon is sometimes seen in some wild fig species as well. See Kislev et al. 2006 a,b;  Lev-Yadun et al. 2006.)

These tiny wasps are closely associated with the unusual fig inflorescence, an enclosed receptacle known as a syconium, which is a hollow sphere lined with hundreds of tiny flowers. One or more female pollinator wasps enter the fig through a small pore (the ostiole) and pollinate the flowers, laying eggs in some of them, and then (typically) die inside the fig. Pollinator wasp larvae develop in galls within the flowers, each consuming the contents of one would-be seed. After becoming adults, pollinator offspring then mate within the syconium and the females fly to another fig to oviposit and pollinate. Emerging males chew holes in galls containing the females and their telescopic abdominal segments are curled beneath the body so that the genitalia may be inserted into the galls. Unlike the females (which must travel to find a new host on which to lay eggs), male pollinator wasps are wingless (typically with vestigial eyes, antennae, and tarsi) and have highly specialized mouth parts for chewing females out of their galls, fighting with other males, and, most importantly, for chewing an exit tunnel for the inseminated female wasps to leave the syconium. 

Although it was once believed that there was a strict one-to-one relationship between each Ficus fig species and a corresponding agaonid pollinator, it is now apparent that fig wasps have frequently colonized new species of figs to the point that many (possibly most) fig species are pollinated by more than one wasp species. In other cases, pollinator lineages have apparently diverged into two species on a single host species.The most common (although by no means the only) deviation from one-to-one specificity is the situation in which two pollinator taxa are geographically isolated across the host range. Given that interspecific hybridization and introgression appear to be widespread among figs, Machado et al. (2005) suggested that the best model for understanding the evolutionary dynamics of the fig-fig wasp mutualism is one in which groups of genetically well defined species of wasps coevolve with groups of genetically less well defined (frequently hybridizing) groups of figs.

Two major modes of fig pollination may be distinguished by differences in wasp behavior and morphology. Actively pollinating species remove pollen they have collected in special thoracic pollen pockets with their forelegs, depositing it on the stigmatic surface of the flower when laying eggs in a fraction of fig flowers. In contrast, passively pollinating species do not have functional pollen pockets or active pollination behavior and pollen is transported on the abdomen instead.

In monoecious fig species (i.e., those in which each individual tree functions as both a female and a male), all syconia are essentially the same and produce both seeds and pollen-dispersing wasps. In the case of functionally dioecious fig species (i.e., those in which different individual trees function as either males or females), female pollinator wasps are attracted to both gall and seed figs and pollinate both types, but their offspring only develop in gall figs (the seed figs produce only seeds, no wasps). Gall figs are functionally “male” because they yield the wasp larvae that disperse fig pollen as adults.  Ovules that would otherwise produce seed instead serve to nourish wasp offspring. On the other hand, seed figs (which contain no male flowers) are functionally “female” because the styles are too long for the wasp ovipositors to reach the ovules, so viable seeds result from pollination. Conservative estimates suggest that fig wasps routinely disperse pollen over distances of over 10 km and that breeding populations of figs constitute hundreds of individuals spread over areas more than 100 square km.

Nonpollinators are also important components of fig wasp communities, having negative impacts on the mutualism. Three distinct guilds of nonpollinators have been identified: gall makers that attack figs from the exterior, gall makers that enter figs as do the pollinators, and parasitoids that attack other fig wasp larvae. Parasitoids have extraordinarily long ovipositors that are capable of piercing the fig receptacle.

(Weiblen 2002; Cook and Rasplus 2003; Machado et al. 2005; Marussich and Machado 2007 and references therein; Zavodna et al. 2007 and references therein; Lopez-Vaamonde et al. 2009; Moe et al. 2011)

  • Cook, J.M. and J.-Y. Rasplus. 2003. Mutualists with attitude: coevolving fig wasps and figs. Trends in Ecology and Evolution 18(5): 241-248.
  • Kislev, M.E., A. Hartmann, and O. Bar-Yosef. 2006a. Early domesticated fig in the Jordan Valley, Science 312(5778): 1372-1374.
  • Kislev, M.E., A. Hartmann, and O. Bar-Yosef. 2006b. Response to comment on "Early domesticated fig in the Jordan valley". Science 314(5806): 1683b.
  • Lev-Yadun, S., G. Ne'eman, S. Abbo, and M.A. Flaishman. 2006. Comment on "Early domesticated fig in the Jordan valley". Science 314(5806): 1683a.
  • Lopez-Vaamonde, C., N. Wikström, K.M. Kjer, G.D. Weiblen, J.-Y. Rasplus, C.A. Machado, and J.M. Cook. 2009. Molecular dating and biogeography of fig-pollinating wasps. Molecular Phylogenetics and Evolution 52: 715-726.
  • Machado, C.A., N. Robbins, M.T.P. Gilbert, and E.A. Herre. 2005. Critical review of host specificity and its coevolutionary implications in the fig/fig-wasp mutualism. Proceedings of the National Academy of Sciences (U.S.A.) 102 (suppl. 1): 6558-6565
  • Marussich, W.A. and C.A. Machado. 2007. Host-specificity and coevolution among pollinating and nonpollinating New World fig wasps. Molecular Ecology 16: 1925-1946.
  • Moe, A.M., D.R. Rossi, and G.D. Weiblen. 2011. Pollinator sharing in dioecious figs (Ficus: Moraceae). Biological Journal of the Linnean Society 103: 546–558.
  • Munro JB, Heraty, J.M., R.A. Burks, D. Hawks, J. Mottern, et al. 2011. A Molecular Phylogeny of the Chalcidoidea (Hymenoptera). PLoS ONE 6(11): e27023. doi:10.1371/journal.pone.0027023.
  • Suleman, N., S. Raja, and S.G. Compton. 2012. Only pollinator fig wasps have males that collaborate to release their females from figs of an Asian fig tree. Biology Letters 8: 344-346.
  • Weiblen, G.D. 2002. How to be a fig wasp. Annual review of Entomology 47: 299-330.
  • Yang, P., Z. Li, Y. Peng, and D. Yang. 2012. Exchange of hosts: can agaonid fig wasps reproduce successfully in the figs of non-host Ficus? Naturwissenschaften. 99: 199-205.
  • Zavodna, M., S.M. Knapp, S.G. Compton, et al. 2007. Reconstruction of fig wasp mating structure: how many mothers share a fig? Ecological Entomology 32: 485-491.
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Life History and Behavior

Life Cycle

A female wasp flies to a fig synconium and enters a hole at one end, causing her wings to break off. The female wasp lays eggs inside the synconium and eventually dies. Larvae take three to 20 weeks to develop. The adult male then chews its way out of the flower in which it hatched and creates a hole in another flower, allowing a female to exit. They mate and the female then moves toward the opening of the synconium. The male wasp enlarges the opening for her, allowing her to escape and fly to another synconium. The male remains inside where he dies. Adults live for only a few days.

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Evolution and Systematics

Functional Adaptations

Functional adaptation

Mutualistic relationship is maintained: fig tree and fig wasp
 

The mutually beneficial relationship between figs and fig wasps is maintained via sanctions for deviating behavior.

     
  "Theory predicts that mutualisms should be vulnerable to invasion by  cheaters, yet mutualistic interactions are both ancient  and diverse. What prevents one partner from reaping  the benefits of the interaction without paying the costs? Using field  experiments and observations, we examined factors  affecting mutualism stability in six fig tree–fig wasp species pairs. We  experimentally compared the fitness of wasps that  did or did not perform their most basic mutualistic service,  pollination.  We found host sanctions that reduced the fitness of  non-pollinating wasps in all derived, actively pollinated fig species  (where wasps expend time and energy pollinating),  but not in the basal, passively pollinated fig species (where wasps do  not).  We further screened natural populations of  pollinators for wasp individuals that did not carry pollen ('cheaters').  Pollen-free  wasps occurred only in actively pollinating wasp  species, and their prevalence was negatively correlated with the  sanction  strength of their host species. Combined with  previous studies, our findings suggest that (i) mutualisms can show  coevolutionary  dynamics analogous to those of 'arms races' in  overtly antagonistic interactions; (ii) sanctions are critical for  long-term  mutualism stability when providing benefits to a  host is costly, and (iii) there are general principles that help  maintain  cooperation both within and among species." (Jandér & Herre 2010:1481)
  Learn more about this functional adaptation.
  • Jandér KC; Herre EA. 2010. Host sanctions and pollinator cheating in the fig tree–fig wasp mutualism. Proc. R. Soc. B. 277(1687): 1481-1488.
  • 2010. Punishment important in plant-pollinator relationship. Science Daily [Internet],
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Molecular Biology and Genetics

Molecular Biology

Statistics of barcoding coverage

Barcode of Life Data Systems (BOLD) Stats
                                        
Specimen Records:1,540Public Records:922
Specimens with Sequences:1,492Public Species:228
Specimens with Barcodes:998Public BINs:184
Species:273         
Species With Barcodes:197         
          
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Barcode data

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Locations of barcode samples

Collection Sites: world map showing specimen collection locations for Agaonidae

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Relevance to Humans and Ecosystems

Benefits

Pollinator

The relationship between fig trees and their wasp pollinators is an obligate pollination mutualism, because the plant and its pollinator are totally dependent upon one another to complete reproduction. The fig fruit is actually a specially adapted inflorescence called a synconium, which conceals many tiny flowers.

Pollination begins when a female wasp, already covered with pollen from the fig in which she hatched and developed, flies to a new fig synconium and enters a tiny hole at one end. In the process, the wasp's fragile wings often break off. Inside the synconium, the female wasp crawls among the female flowers, of which there are two types - one with a short style into which her ovipositor fits, and one with longer styles, in which she cannot lay eggs. The wasp deposits an egg inside the ovary of each of several short-styled flowers; the long-styled flowers are fertilized by the wasp's pollen load as she climbs over them in her search for oviposition sites. Once she has laid her eggs, the wasp remains inside the synconium, where she eventually dies.

The wasp eggs develop within the flowers. As an adult, the male wasp will chew its way out of its own flower and will then create a hole in a female's flower from which she can escape. They mate and the female then moves toward the tiny opening at the end of the synconium. To reach the hole, she crawls over male flowers and becomes covered with pollen. The male wasp enlarges the opening, allowing the female to escape the synconium and to fly to another, ripening inflorescence to begin the process again. The male remains inside where he dies.

  • Quick Guide: Figs and Fig Wasps, J. M. Cook and S. A. West, Current Biology, vol. 15, no. 24, December 2005
  • Figs and fig wasps, S. van Noort and J. Y. Rasplus, Iziko Museums of Cape Town
  • Book of Insect Records: Chapter 25 Greatest Host Specificity, G. H. Schneider, University of Florida, April 15, 1997
  • Fig Fruit Facts, California Rare Fruit Growers, Inc.
  • Fig Wasp (Hymenoptera: Chalcidoidea: Agaonidae, Pteromalidae, Eurytomidae and Ormyridae) and Ficus (Moraceae) Species Richness and Biogeography of Monts Doudou in Southwestern Gabon, Simon van Noort, California Academy of Sciences Memoir, vol. 28, 2004, pp. 217-233
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Wikipedia

Fig wasp

Fig wasps are wasps of the superfamily Chalcidoidea which spend their larval stage inside figs. They can be the pollinating fig wasps or parasitic wasps. The parasitic wasps belong to several groups of the superfamily Chalcidoidea. While the pollinating fig wasps are galler, the parasitic fig wasps display a great range of feeding regime from carnivory (parasitoid wasps) or herbivory (making galls as the pollinating wasps). .

Taxonomy[edit source | edit]

The fig wasps are a polyphyletic group, including several unrelated lineages whose similarities are based upon their shared association with figs; efforts are underway to resolve the matter, and remove a number of constituent groups to other families, particularly the Pteromalidae and Torymidae. Thus, the number of genera in the family is in flux. The family Agaonidae has been recently updated to include all the pollinating fig wasps[1] and the subfamily Sycophaginae.[2] The remaining families such as Epichrysomallinae, Sycoecinae, Otitesellinae, and Sycoryctinae should be included in the Pteromalidae.[2]

The female (left) and male Blastophaga psenes

Morphological adaptations[edit source | edit]

Among the Agaonidae, the female is a normal insect, while the males are mostly wingless. The males' only tasks are to mate with the females while still within the fig syconium and to chew a hole for the females to escape from the fig interior. This is the reverse of Strepsiptera and the bagworm, where the male is a normal insect and the female never leaves the host. The non-pollinating wasps have develop impressive morphological adaptations in order to oviposit eggs inside the fig but from the outside: an extremely long ovipositor.

Most fig inflorescences contain three kinds of flowers: male, short female, and long female. Female fig wasps can reach the ovaries of short female flowers with their ovipositors, but not long female flowers. Thus, the short flowers grow wasps, whereas the long flowers become seeds. In figs of this sort, the crunchy bits in the fruit contain both seeds and wasps. However, several commercial and ornamental varieties of fig are parthenocarpic and do not require pollination; these varieties are not visited by fig wasps.

Pollinating fig wasp (Ceratosolen sp.) collected on Ficus septica from South of Taiwan
Ovipositing non-pollinating fig Apocrypta on Ficus sur, Jan Celliers Park, Pretoria

Life cycle[edit source | edit]

The life cycle of the fig wasp is closely intertwined with that of the fig tree it inhabits. The wasps that inhabit a particular tree can be divided into two groups; pollinating and nonpollinating. The pollinating wasps are part of an obligate nursery pollination mutualism with the fig tree. Both life cycles of the two groups, however, are very similar.

Though the lives of individual species differ, a pollinating fig wasp life cycle is as follows. In the beginning of the cycle, a mature female pollinator wasp enters the immature "fruit" (actually a stem-like structure known as a syconium) through a small natural opening, the ostiole and deposits her eggs in the cavity. Forcing her way through the ostiole, she often loses her wings and most of her antennae. To facilitate her passage through the ostiole, the underside of the female's head is covered with short spines that provide purchase on the walls of the ostiole. In depositing her eggs, the female also deposits pollen she picked up from her original host fig. This pollinates some of the female flowers on the inside surface of the fig and allows them to mature. After the female wasp lays her eggs and follows through with pollination, she dies. After pollination, there are several species of non-pollinating wasps which deposit their eggs before the figs harden. These wasps act as parasites to either the fig or the pollinating wasps. As the fig develops, the wasp eggs hatch and develop into larvae. After going through the pupal stage, the mature male’s first act is to mate with a female. The males of many species lack wings and are unable to survive outside the fig for a sustained period of time. After mating, a male wasp begins to dig out of the fig, creating a tunnel through which the females escape.

Once out of the fig, the male wasps quickly die. The females find their way out, picking up pollen as they do. They then fly to another tree of the same species, where they deposit their eggs and allow the cycle to begin again.

Coevolution[edit source | edit]

The fig-wasp mutualism originated between 70 and 90 million years ago as the product of a unique evolutionary event.[3][4][5] Since then, cocladogenesis and coadaptation on a coarse scale between wasp genera and fig sections has been supported by both morphological and molecular studies.[5][6] This illustrates the tendency towards coradiation of figs and wasps.[5] Such strict cospeciation should result in identical phylogenetic trees for the two lineages [4] and recent work mapping fig sections onto molecular phylogenies of wasp genera and performing statistical comparisons has provided strong evidence for cospeciation at that scale.[4]

Groups of genetically well-defined pollinator wasp species coevolve in association with groups of genetically poorly defined figs.[7] The constant hybridization of the figs promotes the constant evolution of new pollinator wasp species. Host switching and pollinator host sharing may contribute to the incredible diversity of figs.[7]

Genera[edit source | edit]

Fig wasps genera and classification according to the figweb website and recent publications:[1][2][8]

Notes[edit source | edit]

References[edit source | edit]

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