Figs and Fig Wasps
- Written by Marcia Malory
- Category: Rainforests
The common fig, Ficus carica, is the most familiar type of over 800 species of figs, most of them confined to the tropics.
Most figs are trees, but they may also be shrubs, climbers or epiphytes.
The banyan, Ficus benghalensis is one of the biggest fig trees.
Roots growing groundward from its branches thicken into props, allowing the crown to expand indefinitely.
Many figs start life as epiphytes but also send roots down to the ground. These roots grow quickly. The supporting tree is often killed by shade from the fig's crown, by competition from its roots and by the tight binding of interlaced fig roots round the trunk.
The Indian rubber bush tree,or rubber plant, Ficus elastica, whose seedlings are ubiquitous houseplants, can be tapped as a low-yield source of impure rubber, and the softened bark of several African fig trees is used to make cloth,
Fig and Fig Wasp Reproduction
All figs share a similar flower structure.
A mass of tiny flowers is borne inside a more-or-less spherical organ, the fig, which has a stalk at one end attaching it to the tree, and a small opening almost covered in scales at the other.
There are three kinds of fig flowers: male, short-styled female or gall flowers, and long-styled female flowers.
A style is a stalk that extends from the flower's reproductive organ, which supports the pollen-receiving stigma.
Some figs contain all three types of flowers. Other species have figs with long-styled female flowers on one tree and those with male and gall flowers on another.
As the fig develops, the female flowers mature first.
Female fig wasps are attracted by the scent. They fly to the fig and enter through the top opening, forcing their way between the scales.
Once inside, the female fig wasp uses her long ovipositor to bore down through the styles of female flowers into the ovary and deposit eggs. As she does this, she injects a substance that stimulates gall formation. At the same time, she places pollen on the stigma of female flowers.
The wasp's ovipositor is only long enough to reach the ovules of the short-styled flowers. She does not lay eggs in the long-styled flowers; she only probes them and fertilizes them.
Thus, the short-styled fig flowers give rise to fig wasp larvae, while long-styled flowers produce a seed.
As the larval wasps develop and pupate, they produce a substance that stops the fig from maturing.
When the pupae finally mature, male wasps emerge first. They seek out female pupae and fertilize them.
They then make tunnel holes through the fig wall that, up to this time, has been virtually sealed because the scales covering the entrance cling together even more tightly once the female wasps are inside.
The atmosphere inside the fig contains a great deal of carbon dioxide (up to 10 percent compared with 0.03 percent in air).
Once the males have tunneled to the surface the carbon dioxide concentration inside the fig falls quickly and this seems to stimulate both the emergence of female wasps and the opening of male flowers.
In some figs, including the edible fig, female wasps are coated with pollen from many male flowers.
Other species have fewer male flowers, from which the female wasp collects pollen and packs it into special pockets on her body and legs.
The female carries enough stored sperm from her single copulation as a pupa to fertilize all her eggs.
Male and female wasps then join forces to bite away the scales at the fig opening, and the females fly off to find another fig at the female stage. The wingless males, their work completed, die without leaving the fig.
Finally, the fig ripens. Its flesh and many seeds are eaten by birds, bats and monkeys. These animals spread the seeds, which later develop into new plants, when they either drop or excrete them.