Most examples of cooperative behavior in animals involve cooperation between genetically related individuals, which is explained by the theory of "kin selection." Now, researchers have described an example of cooperation between genetically similar but unrelated members of a lizard species common in the western United States. Their findings, published in the June 20 issue of the journal Science, shed new light on the evolution of cooperation and social behavior.
Barry Sinervo, a professor of ecology and evolutionary biology at the University of California, Santa Cruz, has been studying the side-blotched lizard (Uta stansburiana) since 1989. He recently teamed up with French ecologist Jean Clobert to analyze ten years worth of data from Sinervo's ongoing field studies. The two scientists are coauthors of the new paper in Science.
"At first, I thought we were seeing kin selection, so it was astounding to find that the lizards that were cooperating were not related," Sinervo said. "There are many examples of kin selection, but we've found some really nonstandard things happening in this species."
The side-blotched lizard has three different color morphs (a "morph" is a morphologically distinct subset of a species). The orange, yellow, and blue color morphs differ not only in their throat color, but also in their behavior. Orange males are very aggressive and mate with lots of females by taking over the territories of other males--Sinervo calls them "usurpers." Yellow males are "sneakers" who don't defend territories but mimic females and sneak behind the backs of territorial males to cuckold them. And blue males are mate guarders, keeping a close eye on their mates; they recognize and chase off yellow sneakers, but lose out in confrontations with orange usurpers.