The Roles of Vision and the Chemical Senses in Predatory Behavior of the Skink, Scincella lateralis

Abstract

-S-cincella lateralis responds to both visual and chemical cues of prey. A visual stimulus is associated with an increased rate of tongue flicking, orientation to the prey, and attack behavior. Chemical cues are of reduced importance when the visual cue (movement) is present. However, when the visual stimulus of prey is removed, the rate of tongue flicking increases, and is significantly greater in the presence of a prey extract than to a dead prey item or a water control. When prey are non-moving or dead, chemical cues enable the lizard to distinguish potential prey from inanimate objects. A previous study on the relative roles of vision and the chemical senses in prey detection by Scincella lateralis indicate that visual cues stimulate an increased rate of tongue flicking (RTF) and predatory behavior. Chemical cues of normal concentrations (one prey item) do not stimulate an increased RTF or predatory behavior, but if the chemical cue is sufficiently strong an increase in tongue flicking is observed (Nicoletto, 1986). Therefore it appears likely that visual cues are required to release a predatory response and in the absence of visual cues only a super normal chemical stimulus can elicit such behavior. The interaction between vision and the chemical senses in mediating predation is known in snakes (see Burghardt, 1970, 1980; Chiszar and Scudder, 1980 for reviews). There are at least two basic predatory repertoires employed by snakes. Natricene snakes use chemical cues to locate, identify, track, and attack prey (Burghardt, 1970, 1980; Chiszar et al., 1981). Visual cues elevate the rate of tongue flicking and cause orientation, but fail to elicit attack behavior (Burghardt, 1970; Chiszar et al., 1981). Crotalid snakes use visual and thermal cues to locate, identify, and attack prey (Chiszar et al., 1980, 1981; Chiszar and Scudder, 1980), and use chemical cues to track the wounded prey (Chiszar and Scudder, 1980; Golan et al., 1982; Scudder et al., 1983). Thus, both natricenes and crotalids use visual and chemical cues during predation, but the way these cues interact to mediate predatory behavior is different. The objective of this study was to investigate the interaction between visual and chemical cues in mediating the predatory behavior of S. lateralis. This experiment tests the hypothesis that visual cues initiate a sequence of predatory behavior, which will persist in the bsence of visual stimuli if appropriate chemical cues are present. MATERIALS AND METHODS One hundred freshly caught adult S. lateralis (mean snout-vent length = 42.3 mm, standard error = 0.319 mm) were purchased from Snake Farm in La Place, Louisiana in May 1983. Lizards were maintained in three 61 W by 122 L by 61 H cm terraria for two weeks prior to testing. These cages contained a sand and sawdust substrate with pieces of plywood and branches to provide shelter and basking sites. Illumination was provided by Vita-lights and a single 75 w heat lamp per cage permitted thermoregulation. To insure maximum activity during the testing period, the lizards were phase shifted from a natural This content downloaded from 157.55.39.100 on Thu, 25 Aug 2016 05:29:16 UTC All use subject to http://about.jstor.org/terms