KROCHMAL, A.R.*; BAKKEN, G.S.; Indiana State University; Indiana State University: The ecology and phylogenetic distribution of facial-pit mediated thermoregulatory behavior among rattlesnakes (Crotalus and Sistrurus

Pitvipers (Viperidae: Crotalinae) possess unique organs, called facial pits, which allow them to detect subtle temperature fluctuations within their environments. It was previously thought that these organs were used solely to aid in prey detection and strike direction. However, recent work in our laboratory has demonstrated that Western Diamond-backed Rattlesnakes ( Crotalus atrox ) use their facial pits to mediate behavioral thermoregulation under conditions of varying spatial complexity and ecological relevance. To investigate the ecology and phylogenetic distribution of this behavioral phenomenon, we tested the thermoregulaotry performance of six rattlesnake species from an array of habitat types, representing all major rattlesnake evolutionary lineages. We also tested a single non-rattlesnake pitviper as a functional outgroup. All seven species, regardless of habitat type or evolutionary lineage, made successful thermoregulatory decisions when their facial pits were functional, but were unable to do so when their facial pits were temporarily disabled. These findings suggest that facial pit-mediated thermoregulatory behavior represents an ancestral trait among rattlesnakes and does not vary with habitat type. Our results shed light onto the evolutionary origins of the crotaline facial pit.