Wilgers, D.J. & E.A. Horne. 2009. Discrimination of chemical stimuli in

conspecific fecal pellets by a visually adept iguanid lizard, Crotaphytus

collaris . Journal of Ethology. 27:157–163.

This study tested whether the fecal pellets from Collard lizards, Crotaphytus

collaris , carry a chemical signal used in communication among conspecifics. The authors examined whether lizards could detect chemical stimuli and whether there was a differential response to fecal pellets of different individuals. Forty-nine individuals were captured and maintained in separate containers. Each lizard was then randomly exposed to five trials during which they were presented a cotton swab with either 1) water (H20) 2) cologne (COL) 3) a fecal pellet from a conspecific male (MFP) 4) a fecal pellet from a conspecific female (FFP) or 5) the lizard’s own fecal pellet (OFP). To prevent habituation, individuals were tested only once a day every 1-2 days until every lizard had experienced each treatment. During the trials, rate of gular pumps and tongue-flicks was measured along with time until first gular pump or tongue-flick (these behaviors are thought to be associated with olfactory and vomeronasal reception respectively).

The authors found that males responded with tongue-flicks significantly more to female fecal pellets than other samples. This implies that males may use the chemical signals in fecal pellets to infer the presence of potential mates suggesting that there may be some sex-specific chemical deposited in the fecal pellet. In general, there was no effect of treatment on female tongue flicking, while male tongue flicking depended significantly on the specific chemical stimuli presented. Furthermore, weak evidence was found that males respond more with tongue-flicks to conspecific male fecal pellets than to there own suggesting that the fecal pellets may relay information about identity or social status in addition to gender.

The use of chemical signals in these fecal pellets is plausible seeing that we discussed in lecture that secretions from precloacal and femoral glands easily allow for coupling of chemical signals with feces or urine. Because tongue flicks (a method of bringing chemicals in contact with the vomeronasal organ) not gular pumps were affected by treatment, the results of this study imply that although the vomeronasal organ of these lizards is not as developed as in other reptiles, it may still be an important aspect of Collard lizard communication. With the information we learned in class about the kinds of chemicals detected by the vomeronasal organ, we can infer that the chemicals present in the fecal pellets have a large molecular weight so are likely to be lipids, proteins or other non-volatile molecules. Even though this species relies heavily on visual signals for foraging and mate attraction, the chemical signals conveyed in the fecal pellets could still be important in conspecific communication because they provide specific and persistent information which can be deposited at strategic locations.