PLACE, Aaron J.; Oklahoma State University: Is the current function of the rattlesnake rattle changing from an auditory to a composite auditory/visual signal?

Rattlesnakes are an ideal model system in which to study the evolution of defensive behavior. I tested the hypothesis that large body size, the presence of conspicuous tail banding, and aggressive temperament have evolved in concert. Data on maximum adult body size, the presence of tail banding and temperament were collected from the literature. When phylogeny was not considered, there was a significant association between the presence of tail banding and large body size, but not between body size and temperament, nor temperament and tail banding. When correcting for phylogeny using the concentrated changes test, I found that tail banding and temperament were significantly associated (p = 0.022), while size and temperament and size and tail banding were only marginally associated (p = 0.087 and 0.096, respectively). Tail banding and body size were significantly autocorrelated with phylogeny (p = 0.083 and 0.001, respectively), but temperament was not. These data suggest that the rattlesnake rattle may also serve as a visual warning display in the larger, more derived rattlesnakes such as Crotalus atrox. The advantages of multiple signaling modalities are discussed.