The function and evolution of predator scent application: Olfactory camouflage in ground squirrels (Spermophilus spp.)

Animals have evolved diverse antipredator strategies. Most prey animals live in an olfactory world where predators use leaked chemical cues; however, antipredator studies are often visually focused. Here I demonstrate that ground squirrels (Spermophilus spp.) have evolved a unique behavior, predator scent application, where they apply their predators' scents to their bodies to camouflage their own odor. This olfactory camouflage presents a remarkable case of opportunistic exploitation in nature, turning the scent of danger into a protective disguise.;I directly test three proposed functional hypotheses of snake scent application---antipredator, conspecific deterrence, and ectoparasitic defense---in a series of experiments in Chapter Two. I discovered that rattlesnake foraging behavior is reduced by the addition of snake scent to squirrel odor and that neither conspecifics nor fleas are affected by snake scent. The results suggest snake scent application serves as an olfactory camouflage, masking squirrel odor from predators.;Chapter Three consists of a comparative study across multiple squirrel species of application of rattlesnake and weasel scent and examined the relationship of historical (established by fossil records) and present predator presence on the prevalence of the behavior. Species that historically and currently co-occur with rattlesnakes all applied snake scent, however, no such pattern existed for weasel scent application. Ancestral state reconstructions suggest that predator scent application is an ancient trait and imply a homologous evolution of the behavior within the squirrel group. Furthermore, populations with either recent rattlesnake loss or gain do not display the behavior, indicating that relaxed selection from rattlesnake leads to rapid loss of the behavior but that it is not readily regained. Integrating behavior with phylogenetics and paleontology provides a unique perspective to studying the evolution of behavior.;In Chapter One, I present a systematic study of snake scent application in two closely related ground squirrels. I found that both species apply snake scent in a stereotyped pattern, chewing on snake-scented substances (e.g., shed skins) and licking their bodies from flank-to-tail to apply the scent to their fur. I also show that adult female and juvenile squirrels spend more time applying scent than adult males.