Blind Date - The Secret Sex Lives of Figs
Fig trees are sparsely distributed but conspicuous in most African environments where some species may reach gigantic proportions and their substantial crop of figs provides sustenance to a huge array of birds, bats and other creatures.
Fig trees are also noteworthy for their remarkable symbiotic relationship with a family of minute wasps which perform the essential pollination service while undergoing their own reproduction. Southern and East Africa support about 50 species of fig and there many more in central and west Africa. In some countries, a variety of exotic fig species from other parts of the world are grown as ornamental plants, and the Edible Fig is cultivated in some areas.
Figs have evolved a unique relationship with a family of tiny agaonid wasps, which serve to pollinate the equally tiny flowers 'hidden' within the fig capsule . Each species of fig has its own specific wasp partner and cannot be fertilised by any other means.
The process of pollination begins with a winged female wasp (bearing pollen from another fig) squeezing into a tiny hole at the tip of the fig, and entering the dark chamber. Inside, there are numerous female flowers of two kinds, one kind with a shorter stigma than the other. The female wasp searches for a short-styled flower and while clambering around in the dark, she offloads her pollen load onto female flowers with long stigmas which are then fertilised to produce a seed. Once the wasp has selected a short-styled flower she inserts her thin egg-laying device known as an ovipositor , and deposits an egg into the ovary of the flower. Her wings broken from the tight squeeze into the fig, and her reproductive job complete, the female wasp weakens and dies.
In the meantime, the little egg inside the flower develops into a larvae and then a wasp, either male or female. The male wasps are armed with strong jaws and are able to bite their way out of the flower, but have no wings and can never escape the darkness of the chamber into which they have emerged. Their role in life is short but sweet - a 'blind date' in which they are genetically programmed to gnaw into a flower containing an imprisoned young female wasp, impregnate her, and in so doing, liberating her through the hole that he creates. The female may lack strong jaws, but she has wings, and now laden with eggs she moves in a determined fashion towards the pin hole of an opening at the tip of the capsule. At this time in the development of the fig, the cluster of male flowers ripen and their pollen-laden anthers face upward in such a way that female wasp accumulates the pollen on herself. A row of bracts delay her escape but once again, the male wasp comes to her aid as he chomps through the wall of the fig to enlarge the opening. This one last act signals the end of his desperately short life life, and he dies inside the chamber alongside the previous generation of females. The young egg- and pollen-bearing female now sees the light of day and stretches her fragile wings to fly off to another fig. Astonishingly, this whole process takes just a few weeks and the adult female wasps may not live for more than a few hours.
Once the female agaonid wasps have found their way out of the receptacle, the inflow of air causes the fig to swell and ripen.
Feeding the Multitudes
In order to propagate itself, the fig tree, like any plant, must disperse its seed. The seeds are set within the fleshy 'fruit' that is rich in carbohydrates and high in moisture. The abundant crop of figs - as many as 100 000 on large trees - attract all manner of frugivorous animals which digest the flesh and then distribute the seeds in their droppings.
Among birds, the colourful African Green Pigeon is the greatest fig addict, but the turacos, larger hornbills, barbets, mousebirds, bulbuls and starlings all relish the crop and are highly enthusiastic feeders. Even insectivorous birds such as flycatchers and warblers are attracted to fig trees, snapping up the agaonid wasps and other insects attracted to the bounty. Epauletted fruit bats and monkeys are the mammals most excited about figs, but duiker, bushbuck and bushpig are all attracted to the ripe figs that fall from the branches.
A closer inspection of the animals attracted to fig trees reveals an intricate food chain, with the lives of creatures as diverse as dragonflies, geckos and civets being wound up in the complex web of life. Next time you come across a fig tree bearing ripe figs, stick around a while, and watch the action.
Fig Fact File
All figs belong to the genus Ficus, with about 750 species world-wide.
Ficus is part of the family Moraceae which contains 75 genera and are to be found mostly in the tropical and sub-tropical parts of the world.
Figs vary in form from enormous free-standing trees and epiphytic stranglers to low shrubs and stunted rock-splitters.
All figs are characterised by having a milky sap or 'latex' in their stems and leaves, and a distinctive sheath (known as a stipule) covering the growth tip of new leaves.
Fig trees have a unique flower and fruit structure, with the tiny inflorescence being housed within a fleshy receptacle known as a syconium. The syconium is not, then, a fruit (in the true sense of the word) although it certainly serves the same function from an ecological perspective.
Posted: Plants by CC Africa, Date: 21 November 2006