Effects of chemical and visual exposure to adults on growth, hormones, and behavior of juvenile green iguanas.

For 1 year, groups of juvenile male green iguanas (Iguana iguana) were housed such that one group was visually exposed to an adult female, a second group was both visually and chemically exposed to an adult female, a third group was visually exposed to an adult male, and a fourth group was both visually and chemically exposed to an adult male. Juvenile males exposed to signals from adult males showed signs of chronic stress, including reduced growth rates, lower testosterone levels, higher corticosterone levels, and decreased frequencies of headbob display. Although visual exposure alone was sufficient to suppress growth, testosterone levels, and rates of display, the addition of chemical exposure strengthened some of these effects. Both chemical and visual exposure to an adult male were necessary to produce elevated corticosterone levels. In contrast, juvenile males exposed to visual and chemical signals from an adult female exhibited growth rates, hormone levels, and behavior patterns typical of juvenile males housed in the absence of adults of either sex. These results suggest that visual and chemical signals from dominants may serve to reinforce social relationships among males through their influence on the physiology and behavior of receivers.