Fig-Wasp Mutualism

The deeper biologists delve into the workings of nature, the more they come to appreciate and understand the complexity and entanglement that exists between species. No living entity is in isolation. Every plant and creature has a relationship with and depends upon countless other life forms around it. The web of life connects us all, with varying degrees of interdependency.

Remove one species and there will be manifold types of impact on all species connected to it—even those remotely connected. The web of life has evolved to be so interdependent that if one link is severed, the whole thing might not collapse but it will surely change. We humans are causing the ongoing extinction of numerous species every day, with little comprehension of how we are upsetting the exquisite balance of nature.

Mutualism is the strongest kind of tie between two species, wherein both of them benefit from and depend on each other. Pollination is a common type of mutualism. For example, most flowering plants depend on bees, birds, and bats to spread pollen to other plants of the same species—completing the process of sexual reproduction. In return, the plant may offer the pollinator sweet nectar or some of its pollen for food. If the critter is pleased with the meal, it will fly off—carrying some pollen with it—to seek another plant of the same species, and thus fulfilling the sex act.

Modern agriculture relies heavily on bees for pollination of fruits and vegetables. Many bee colonies are being decimated in the last few years, however, and agricultural folks are in a panic. Is the bee-plant balance being degraded?

Some plant-pollinator mutual relationships evolve to become so specialized that only one kind of insect is able to pollinate one kind of plant. They become completely dependent on each other. If one goes extinct, the other must follow. There are numerous species of tree for which there are no further offspring possible, because their pollinator has died off. On the island of Mauritius, for example, there have been no tambalacoque saplings for some 300 years, because the dodo bird—which once spread the tree’s seeds—went extinct in the late 1600s, having been hunted down by people who arrived on the island. Only ancient tambalacoque trees are left. Soon they may also be gone (unless a new pollinator can step in).

One of the more spectacular examples of complete mutualism exists between fig trees and the wasps that pollinate them. There are some 750 species of fig tree around the world (mostly in tropical climates) and 750 species of wasp—one for each kind of fig. The fruit of the fig is hollow, with one end open and with a tiny array of flowers inside the fruit. The wasp climbs inside, lays her eggs on a flower and promptly dies. Later, her eggs hatch, larva eat some of the flower’s seeds, and pupate. Yet later the adult wasps emerge, mate, and the males then promptly die. The impregnated females—now coated with pollen, as they’ve mucked around inside the flower for some time—fly off to find another fig tree of the same species, crawl inside the fruit, and pollinate its flowers.

I don’t believe that such an exclusive example of mutualism exists around me. Most local plant and animal species are generalists. But I can’t help watching a bee or butterfly, loaded with pollen, and wish that it fly on and visit many kinds of flowers and help to bring about more of them. And I can’t help but wonder what delicate examples of mutualism do exist around here, that are in danger of being interrupted. Every critter is precious!