Behavioral adaptations to pathogens and parasites: five strategies.

The ever present threat of viral, bacterial, protozoan and metazoan parasites in the environment of wild animals is viewed as responsible for the natural selection of a variety of behavioral patterns that enable animals to survive and reproduce in this type of environment. Several lines of research, some quite recent, point to five behavioral strategies that vertebrates utilize to increase their personal or inclusive fitness in the face of parasites (broadly defined to include pathogens). These are: 1) avoidance of parasites; 2) controlled exposure to parasites to potentiate the immune system; 3) behavior of sick animals including anorexia and depression to overcome systemic febrile infections; 4) helping sick animals; 5) sexual selection for mating partners with the genetic endowment for resistance to parasites. The point is made that to consider a behavioral pattern as having evolved to serve a parasite control function the parasite or causative agent should be shown to adversely impact the animal's fitness and the behavior in question must be shown to help animals, or their offspring or group mates, in combating their exposure, or reducing their vulnerability, to the parasite.