Scientists have reported the first direct evidence that cooperative behavior in side-blotched male lizards arises from their genes. The findings, published in the May 9 Proceedings of the National Academy of Sciences by University of California–Santa Cruz’s Barry Sinervo and colleagues, represent some 20 years of research into the altruistic or “self-sacrificing” behavior.
Side-blotched lizards, it turns out, come in three different throat colors–blue, orange or yellow. Sinervo had previously demonstrated the three throat colors in the males correlate with strikingly different behaviors.
The blues form partnerships, while the oranges are aggressors and the yellows are sneaky.
Say a pair of blue-throated males, for example, is protecting its territory from roaming orange-throated bullies. In a true act of selflessness, one blue throat steps forward to battle an intruding orange aggressor–thereby sacrificing his own chances to successfully mate.
Meanwhile, as blue throats and orange throats battle it out, yellow throats quietly sneak into unprotected territories to find females.
In nature, altruism seems contradictory to an animal’s goals of survival and passing on its genes, so researchers have been trying to understand why one of the blue males in a partnership will put himself in harm’s way to allow the other to reproduce. Even though it may forfeit their own reproductive chances, the fighting blue throats secure the persistence of their genes in future generations by enabling their blue buddies to avoid the aggressors and go on to mate.
By studying the genomes of male lizards of each throat color, Sinervo provided direct evidence that besides throat color at least three other genetic factors underpin the self-sacrificing behavior.
Mark Courtney, whose program in the National Science Foundation’s biology directorate supports Sinervo’s research said, “On the surface, cooperation in the absence of close-relatedness can seem to be evolutionarily counterproductive–but Sinervo explored the genes that underlie cooperative behavior and discovered how they can affect the genetic composition of future generations.”
Courtney attributes Sinvervo’s long-term commitment to research in this area as key to teasing out the complexities of the system.