Figs and their pollen carriers, fig-wasps have become very popular at least among biologists. Their relationship, in which we can see another extremely complicated relationship in nature, contains one of the hidden keys needed for solving the mysteries of co-evolution and the ecosystem.
This mutual relationship is believed to have begun about 90 million years ago, and approximately 750 varieties of figs (Ficus) now thrive. Amazingly, as a new kind of fig evolves,
a fig-wasp corresponding to that new kind of fig appears. But a complicated co-evolution like this can be explained by Darwin’s theory of evolution, just as other happenings in nature can. His theory suggests that every creature evolves to leave the largest number of descendants in the next generation.
Plants, which have animals carry their pollen, offer the carriers a reward such as honey, or provide a carrier’s larva with a place to grow. Cabbage leaves rich in nutrition didn’t evolve to be a salad, but to be host food for larva of butterflies that carry cabbage pollen. Unfortunately, such larva become a horticulturist’s enemies.
The relationship between fig and fig-wasps in which an insect carries pollen and its larva eats the fruit is also seen in the cycad group and the yucca plant, a plant growing in arid areas in America. In this relationship, a contradictory relationship exists; that is, more pollen carriers are active more eggs are laid, and therefore more seeds are eaten even though the carriers help the plant bear fruit.
Fig flowers, which have the egg of a fig-wasp become a gall (an insect’s knot), food for larva, and fig flowers which don’t have an egg become seeds if they are pollinated. The number of female fig-wasps that develop into adults and fly out of the fig plant carrying pollen represents the number of carried pollen; that is, the adaptation rate of the male fig (the rate used to measure the size of the population of a certain genetic model in the next generation).
The number of seeds indicates the adaptation rate of a female fig. On the other hand, to become a host plant for male fig-wasps is fruitless for figs because male fig-wasps don’t have wings and can’t carry pollen. Therefore, figs don’t want to have too many male fig-wasps. Ideally, figs want to produce about the same number of female fig-wasps and seeds to create a balance between the number of female fig-wasps and fruit for themselves. On the other hand, fig-wasps want to lay as many eggs as possible to obtain the greatest possible benefit. Both the figs and fig-wasps co-exist by maintaining this subtly balanced relationship.
If the figs have a pollen carrier in all their flowers, no seeds will be left for the next generation. On the contrary, if figs reject pollen carriers too often, there won’t be enough pollen carried out for pollination. They both need to maintain this relationship. Some figs are heterosexual 
so male figs raise fig-wasps to carry pollen and female figs fruit seeds. Fig-wasps can’t mate in the female fig syconium, but the wasps can’t distinguish a male syconium from a female syconium. And the wasps that unfortunately come into a female syconium only help the fig pollinate.
Throughout the world, figs grow most abundantly in the forest of Ranbil on Borneo Island in Malaysia, and about 80 varieties of figs can be observed there. While we were studying there in 1998, there was a drought, and no fig flowers bloomed during that time. On that occasion, we made an interesting observation that fig-wasps came back right away as the flowers of the homosexual figs revived, but the wasps took two to three years to come back to the flowers of the heterosexual figs. Who knows when a change of weather in the tropical rainforest will create a new condition and give us clues to solve this mystery? I can’t take my eyes off the Ranbil forest.
