Forget about love, flowers, chocolates, teddy bears, etc. etc. Common side-blotched lizards decide on their Valentines by playing rock-paper-scissors. True story.
Here are three specimens of this species, Uta stansburiana, from our collection, HERR 7589, 7594, and 7595, collected in Texas in 1971:
So the way this crazy love (or not... love...) game works is like this. Male common side-blotched lizards come in three different forms. There are orange-throated males, yellow-throated males, and blue-throated males. Here's a pic, taken from the website of Barry Sinervo, one of the biologists who first figured out the rules of this lizard's game.
Orange-throated males are largest and the most aggressive of them all and as such they're able to defend large territories with lots of females in them. They can easily overpower the blue-throated males, which are of a medium build.
Orange-throated males cannot defend against yellow-throated males, however. Yellow-throated males are the smallest of them all and look like females! Given this, they're able to sneak into the territories of orange-throated males unnoticed and mate with any of the females there who might be tired of bloated orange-throated machismo.
The stealth strategy of the yellow throats is powerless, however, against the medium-size blue-throats. The blue-throated males keep small territories and work together to guard their females. As a result, the yellow-throated males can't fool the watchful blue-throats like they can with the orange-throats.
So to sum up, orange beats blue, blue beats yellow, and yellow beats orange. Pretty cool if you ask me.
The success of these different mating strategies depends on the the rarity of each form in a given population. For example, if there are too many yellow-throated males, their "sneaker" strategy becomes ineffective, because well, it's not very sneaky anymore if everyone is doing it, too. So the prevalence of any given form will cycle every few years in a given population of common side-blotched lizards. In some years, there will be more blue-throated males, other years more orange-throated males, and in other years, more yellow throated males. When one form becomes too common, the others start to be more successful.
Sinervo, B. and Lively, C.M. 1996. The rock-scissors-paper game and the evolution of alternative male strategies. Nature 340:240-246
Corl, A., Davis, A. R., Kuchta, S. R., Comendant, T. and Sinervo, B. 2010. Alternative mating strategies and the evolution of sexual size dimorphism in the side-blotched lizard, Uta stansburiana: a population-level comparative analysis. Evolution 64: 79–96.