Side-blotched lizards (Uta stansburiana) are a small lizard species found in many states in the American West and Mexico. Males come in three varieties, each with a different throat color: orange, yellow or blue. Those throat colors announce to the lizard world what mating strategy a male will use. Orange-throated males are bigger and more aggressive, and they have large territories with several females. Blue-throated males have smaller territories with only one female, and they cooperate with other blues for defense. Yellow-throated males, whose markings and behaviors mimic those of females, are known as “sneakers”; they don’t keep a territory but instead cluster around and sneak into the territories of other males to mate with their females.
And like a big game of rock-paper-scissors, each variety has its pluses and minuses in the mating game. The result is that once every few years, the original study in Nature found, the dominant variety changes.
If we start with the orange males, they have the advantage over blues in terms of territory size and numbers of females they control. But with more territory controlled by orange males, the more opportunities for sneaky yellow males to mate, and then the yellow population begins to grow. But the yellows are vulnerable to the blues, who can easily defend their females because they cooperate with other blues, so then they take over. But then oranges mate with more females and grow in numbers again. Orange is most successful when blues are greater in number; yellows are most successful when oranges are greater in number; blues are most successful when yellows are greater in number. The result is a cycle that has persisted for millions of years.
But not everywhere. Further research into this species, published in PNAS, has found that there are many populations of this species that have lost one or two of the color varieties. The yellows were always the first to go; something (not yet known) had changed the game’s rules so that they no longer had any advantages over orange or blue. Some places had also lost their oranges and others had also lost their blues. And that loss of a color variety or two had further consequences: It was accompanied by rapid changes in traits like body size in the remaining lizard types, changes that could lead to the evolution of new species.
These lizards came up in a conversation among some of my friends earlier this year (a mathematician in the group told me about the lizards, which, along with the rock-paper-scissor game, have been studied in game theory). One of them was wearing a rock-paper-scissors-lizard-Spock T-shirt, illustrating that lesser-known variant of the game. I am disappointed to report, however, that I was unable to find any link between it and the discovery of the lizards’ mating strategy.