Meeting Abstract
The expression of male secondary sexual traits can be dynamic, with traits changing size, shape, or structure over the course of different seasons. However, the factors driving such changes are often poorly understood. For example, the size of a morphological secondary sexual signal, the dewlap or throat-fan, in male Anolis carolinensis lizards changes seasonally within individuals, with males exhibiting overall larger dewlap areas in the spring relative to the winter. A previous study showed that this size change is likely not due to differential resource allocation, as limiting resource availability did not affect dewlap size in young males. In this study, we tested the hypothesis that seasonal changes in male dewlap size are driven by increased use and extension of the dewlap in spring and summer, when males are breeding, relative to the winter and fall. We captured male green anole lizards in early spring prior to the onset of breeding and physically constrained the dewlap in half of them such that it could not be extended. We measured dewlap area in the spring, summer and fall, as well as the elasticity of dewlap skin relative to belly skin. We show that dewlaps in unconstrained males increase in area from spring to summer and then shrink in the fall, as seen in male green anoles in nature, whereas the dewlaps of constrained males consistently decrease in size from spring to winter. We also show that dewlap skin is significantly more elastic than belly skin. Finally, we discuss the likely importance of the mechanical properties of signalling structures for signal evolution and design.
