Chemosensory Identification of Lizard-Eating Snakes in the Desert Iguana, Dipsosaurus dorsalis (Squamata: Iguanidae)

Abstract

Many antipredator behaviors function by hindering the ability of a predator to catch or consume prey once they are encountered. However, prey may also reduce predation risks by detecting predators before an encounter occurs. We tested the ability of the desert iguana (Dipsosaurus dorsalis) to detect and identify snake predators via chemoreception. Desert iguanas were exposed to chemicals from two sympatric snake species. The California kingsnake (Lampropeltis getula californiae), a species known to feed on lizards, was used as the predator stimulus, whereas the western shovel-nosed snake (Chionactis occipitalis), which feeds only on arthropods, served as a control for a general response to snake chemicals. Lizards were placed in terraria that previously housed live snakes or had been treated with distilled water or a pungent control. Overall tongue extrusion frequency and number of tongue extrusions prior to movement increased in response to chemicals from the California kingsnake but not in response to the western shovel-nosed snake. In addition, desert iguanas exhibited unusual slowness of movement and adopted a distinctive body posture in response to the predator stimulus. These results demonstrate that desert iguanas can detect chemical deposits from snakes and can discriminate between a snake species that feeds on lizards and one that poses no threat. In addition, the resulting low posture and slow movement may facilitate crypsis as the lizards attempt to gain information regarding the predator. Desert iguanas are herbivorous lizards and may use chemical cues to detect and avoid snake predators while foraging or when entering burrows.