Social significance of ventrolateral coloration in the fence lizard, Sceloporus undulatus

The blue ventral colour patches of the fence lizard, Sceloporus undulatus, long believed to be involved in intraspecific communication, allow males to recognize the sex of conspecifics. This was demonstrated experimentally by a field study in which tethered lizards were introduced singly to free-ranging adult males. Males identified those conspecifics having blue belly and throat patches as male, and those that had white belly and throat patches as female. Six experimental groups of tethered lizards consisted of unpainted lizards of each sex, lizards of both sexes painted to match their normal ventral colour patterns, and lizards of each sex painted to match the ventral coloration of the opposite sex. Males responded to unpainted lizards by directing agonistic behaviour to males and courtship to females. Their responses to lizards painted to match the ventral patterns of their own sex were virtually identical to their responses to unpainted lizards, indicating that painting alone did not alter their reactions. Males painted to resemble females in ventral coloration were courted in all but one trial; females painted with the ventral pattern of males were all subjected to aggressive behaviour. Responses to both groups bearing colours of the opposite sex were significantly different from those to unpainted members of their own sex, but were nearly identical to those normally elicited by the opposite sex.