Science - November 20, 2009

Termites thrive on monocultures

The fungus-growing termites of Africa know what they like. They only grow one kind of fungus in their gardens. A Wageningen scientist tell why in this week's Science.

Termites are the superfarmers of the animal kingdom. Termite hills conceal extensive gardens in which fungi are cultivated. Within each colony it is always the same fungus. So termites favour monocultures. The question is what this preference is based on. Wageningen evolution biologist Duur Aanen (Genetics) and his Danish colleague Koos Boomsma have found an answer to this question.
A termite royal couple start a new colony without any fungus. The fungus has to come from outside. Worker termites bring home the fungus by carrying in spores when they've been out foraging. These are spores of various genotypes. And yet it is always just one genotype that survives in the colony. Aanen and Boomsma shown that the species of which there happens to be the most defeats the scarcer fungi.
Same neighbours
volution theory predicts that a symbiosis between multiple fungi species will be unstable. The fungi will compete with each other instead of cooperating with the termites. The new study shows that there is a special mechanism to prevent this. The crux is that genetically identical mycelia fuse if they grow alongside each other.  And the chances of fusion occurring are greater if there are lots of the same fungus side by side.
The fusion makes spore formation more efficient. And those spores provide not just food for the termites but also grafting material for their farms. The researchers believe that it is this selection that eventually leads to a lifelong relationship between a colony and one particular fungus.