Getting beaten up by the neighborhood bully so your buddy can spend time with the ladies may seem like a rough life, but that strategy not only works for some lizards, it also gives a fascinating peek into hard-wired altruism in evolutionary biology.
Side-blotched lizards spend their year on earth looking to reproduce, and their strategies have lessons about evolution. An article in the May 9 edition of the Proceedings of the National Academy of Sciences provides the first genetic evidence of a trait that the animals recognize and use – even if that trait seems on the surface to be counterproductive.
“Cooperation is a tricky thing in terms of evolutionary theory,” said Andrew McAdam, an assistant professor of fisheries and wildlife and zoology at Michigan State University and one of the paper’s authors. “The question then is why do some organisms cooperate when it seems like being selfish should be the best strategy?”
Turns out, it’s all in the genes.
For two decades, Barry Sinervo from the Department of Ecology and Evolutionary Biology at University of California – Santa Cruz (the study’s lead author) has been studying side-blotched lizards of the Central Valley of California, funded by the National Science Foundation. Males break down into three throat colors, flagging different behaviors, which Sinervo has discovered follow “rock-paper-scissors” cycles of lizard lust.
Orange-throated lizards are the big bullies, roaming far from home to raid female territories and mate. They generally beat blue-throated lizards, the stay-at-home dad types. The blues stick close to home to protect females and have a buddy system. One blue-throat will do battle with the orange-throat, enabling his buddy stay fit and mate. McAdam explains that the altruistic blue-throat does this, even though as a result he will sire few, if any, offspring.
The yellow-throated lizards are sneakers – they casually sneak into female havens and mate without calling a lot of attention to themselves. Blues “beat” yellows because they’re close to home keeping watch. Yellows “beat” orange because the bullies aren’t sticking close enough to home to keep an eye on things.
Research has focused on why the blue throats are willing to cast aside their own opportunities to procreate for the benefit of a friend.
“Why not abandon them and become loners – why not go it alone?” McAdam said. “The blue throats can set up new territories and be successful. That’s the evolutionary puzzle that we needed to solve.”
Gene mapping revealed that the male blue-throats who buddied up are not even remotely related – yet still share many genes. Somehow, McAdam said, the altruistic lizards know they’re working to pass on their genes, even though their partners aren’t family. The tag-team approach does effectively thwart the orange-throat bullies, albeit at a personal cost.
The term “greenbeard” refers to an evolutionary term of a trait so obvious that others can recognize The greenbeard in this case, McAdam said, is more than just a blue throat. The mechanism of self identification could be smell, or possibly body language. The lizards have a head-bobbing action that might be signaling genetic simpatico.