Blue-throated cooperative lizards

By mikelove, published at 10 May 2007 - 8:12pm, last updated 10 years 40 weeks ago.

A very odd article on the evolution of cooperation in a population of color-coded lizards!

The paper describes unrelated male lizards that form cooperative partnerships to protect their territories. These partnerships are often mutually beneficial, enabling both partners to father more offspring than they would on their own. Under some circumstances, however, one male in the pair may have few or no offspring as a result of protecting its partner from the aggressive intrusions of other lizards.

In side-blotched lizards, the greenbeards have blue throats. This species comes in three different throat colors--orange, yellow, and blue--and throat color corresponds to different territorial behaviors in the males. Blue-throated males form partnerships in which two males cooperate to protect their territories; orange-throated males are highly aggressive and usurp territory from other lizards; and yellow-throated males sneak into the territory of other males to mate with females.

Previous research by Sinervo and his collaborators has demonstrated that these strategies result in a kind of "rock-paper-scissors" game in which orange defeats blue, blue defeats yellow, and yellow defeats orange. The lizard populations go through cycles in which one color after another increases its numbers at the expense of the others, but none are able to maintain dominance.

"One of the big problems in the evolution of altruism is explaining how it gets off the ground in the first place," said Alexis Chaine, a graduate student in ecology and evolutionary biology at UCSC and a coauthor of the paper. "This is a situation that oscillates between mutualism and altruism, depending on the circumstances. Periods of mutualism give a much-needed boost at early stages in the evolution of altruistic genes and also provide long-term stability to the cooperative relationship."