The Evolution of Cooperation

Mungermulticell_HL Dave Munger in Seed:

Suppose you were imprisoned in a room with no food supply except for a huge trough of maple syrup. How long do you think you could survive? Sure, the syrup would provide plenty of energy for basic bodily functions, but it would perhaps be only a few months until scurvy or other nasty diseases of malnutrition ravaged your body. Without the ability to somehow produce vitamins and amino acids necessary for survival, consuming a food composed of just sugar and a few minerals likely wouldn’t sustain you for even a year.

Yet many animals do survive on very limited diets, and they have no more ability than you do to produce the basic building blocks of life. Last week, microbiology researcher Ryan Kitko pointed out that the candy-stripe leafhopper thrives while consuming only the xylem and phloem of plants—sap. So how do sap-sucking insects like leafhoppers and aphids survive? Kitko points to two studies on a type of leafhopper commonly known as sharpshooters. Researchers found cells in sharpshooters that were jam-packed with bacteria, which converted the raw materials from sap into the vitamins and amino acids the insects need to survive.

The glassy-winged sharpshooter has two different resident bacteria, each of which creates different nutrients for the host insect from its base diet of plant sap. The bacteria are transmitted directly from the mother to her eggs, so young insects hatch with all the apparatus they need to live on plant sap alone. The bacteria, in turn, have very limited genomes. They wouldn’t be able to survive without the host insects to provide protection and a ready supply of food. In fact, the two bacteria that provide nutrients for the sharpshooter themselves have complementary genomes, each having lost formerly essential sections of their genome now found in the other. The bacteria not only produce nutrients for the host, but also depend on each other’s presence to get the nutrients they themselves need.