What’s All That Head-Bobbing About?

Anolis sagrei displaying. Photo by Valerie Simon.

Anoles are renowned for their displays in which they do pushups, bob their heads up and down, and unfurl their colorful dewlaps. Indeed, the internet is awash with videos of such behavior (here’s a good one of A. sagrei including some cool “slo-mo”; here’s a vicious fight with audience commentary; and for the pacifists out there, here’s a solitary brown anole displaying).

But what’s all the displaying about? And, more specifically, is there any significance to how much a particular male displays? Years ago, Leal showed that in A. cristatellus, the rate of display correlates with endurance–males with the right stuff display longer to predators, perhaps to suggest to them that they look elsewhere for an easy meal. Similarly, Perry et al. found in the same species that in social encounters in the lab, winners both displayed more and had higher endurance than losers. So, rate of display may be an honest signal of physiological capacity. But what happens in nature?Anoles primarily display in social encounters. Does the rate at which they display correlate with the outcome of their social interactions?

Turns out it does. Valerie Simon watched male A. sagrei at a number of sites in Florida and the Bahamas (where they occur naturally). She found that in male-male encounters, the male that did more headbobs won, whereas the one that did more head nods (a submissive behavior in intra-individual interactions) usually lost. In courtship encounters, the more a male bobbed, the more likely he was to get lucky. One can always spin adaptive stories–if high bob rates indicate a fitter male, then both winning in intra-male contests and convincing a female to mate are expected outcomes. Certainly plausible, and worth further study, though how to do so in a non-correlative fashion is not obvious.

Simon also found one–at least to me–unexpected result: males dewlapped more in courtship encounters in which they failed to mate than in those in which mating was achieved. She suggests that high rates of dewlapping may have been directed to unfamiliar females, perhaps to bring them into a receptive frame of mind later on. Maybe so, or maybe just a sign of frustration.