Anoles have served as great model organisms in studies of adaptive radiation and how form and function are molded by selection, but they have also been the center-piece for some of the most interesting (and classic) research on how the brain modulates aggression to determine dominance. For example, work by Cliff Summers and his laboratory (among others) over the years has provided great detail concerning how adrenal catecholamines and glucocorticoids, produced during “stressful” aggressive interactions, interact with serotonergic activity in the hippocampus to determine social rank. These neuroendocrine processes are outwardly expressed, in a sense, by the familiar eyespot seen prominently during male green anole (Anolis carolinensis) interactions. The formation of the eyespot is stimulated by catecholamines, and the latency of eyespot formation is dependent on serotonergic activity, which is influenced by glucocorticoid secretion. Males that develop the eyespot sooner tend to be dominant, and once eyespots have appeared in one combatant, aggression in the rival tends to be inhibited. At least that’s the way it seems to work in A. carolinensis.
Technical details aside, the relevant point here is that eyespots form during bouts of stress, which can include participating in intense agonistic interactions with rivals or being noosed and processed by a biologist. The latter scenario is how my colleague Matt Lovern and I noticed on South Bimini (The Bahamas) that A. smaragdinus males develop a shoulder patch, but not an eyespot during stress. We did not see eyespots during male-male interactions, but we could have missed them. Since A. smaragdinus and A. carolinensis are relative closely related, we began to wonder about the evolutionary significance (and distribution) of this type of signal. The sympatric A. distichus, A. sagrei, and A. angusticeps were not observed to have either eyespots or shoulder patches. Adding to our curiosity, a recent post on Anole Annals showed the closely related species A. porcatus/carolinensis (Strange Perch Mate) with both an eyespot AND a shoulder patch!
What species of anoles have eyespots and/or shoulder patches? Do they have similar functions as in the green anole? We know from Jonathan Losos’s very first paper that the distantly related A. marcanoi has eyespots, but what about the rest? We would love to hear from other anole biologists about their observations of eyespots (or lack thereof) and/or shoulder patches in other anole species. Such a comparison may have interesting insights into the evolution of neuroendocrine regulation of social behavior, which we know varies widely among anole species.