Microbes, Herbivory and the Evolution of Social Behavior
Department of Zoology, University of California, Davis, Califorrnia 95616, U.S.A.
Herbivorous animals that digest plant structural tissues almost invariably depend on the fermentative activity of symbiotic populations of microbes, housed in the digestive tract, to degrade plant fiber. The evolution of microbial fermentation systems entails an intricate coevolution among microbe species, as well as between microbes and herbivores. Beyond some level of biochemical specialization, fermentative microflora cannot survive outside of the host’s body, and can only be transferred among herbivores by close contact. Yet in order actually to coevolve with the herbivore species, the microbe populations must be transmitted from one generation of herbivore to the next. In order to evolve the most effective system for utilizing plant materials for food, i.e. dependence on a microbial fermentation system, herbivores must concurrently evolve behavioral adaptations that ensure contact between generations. The evolution of social systems in a variety of animals, from termites to dinosaurs, may be originally associated with their herbivorous habits.