We’ve all seen anole lizards extend their dewlaps, but the social displays of the many species of anoles also include the erection of a dorsal crest. But, what underlies the formation of these crests? Although many of us have talked about this, undergraduate John Ficklin, along with Morgan Gerace and Dr. Matthew Rand, all of Carleton College, aimed to find out and presented their work today at SICB. By injecting Anolis sagrei and A. carolinensis lizards with isoproterenol (a β-adrenergic agonist), they caused crest erection in males, but not in females. They then used histological techniques to examine the cellular morphology of the crest. What they discovered is that male anoles have a clearly-defined organ they dubbed the “crest capsule” (a structure female anoles lack), and when this capsule is filled with an edema from local blood vessels, the crest extends vertically. Collagen fibers appear to help maintain the crest’s vertical orientation during its display. After inflation, the edema then drains into the subcutaneous space surrounding the capsule, causing the crest to deflate. They found no evidence of the involvement of muscles, cartilage, or vascular sinus in crest erection.
In sum, John Ficklin and his colleagues have solved one of the big questions of anole display!