Visible sympathetic activity as a social signal in Anolis carolinensis: Changes in aggression and plasma catecholamines

Darkening of postorbital skin in Anolis carolinensis occurs during stressfu l situations and is stimulated by sympathetic activation of beta (2)-adrene rgic receptors via adrenal catecholamines. This eyespot forms more rapidly in dominant males during social interaction. Eyespot darkening (green to bl ack) appears to function as a social signal communicating sympathetic activ ation and limiting aggressive interaction. To assess the value of the eyesp ot as a social signal, males were painted post-orbitally with green, black, or red paint. Each male was exposed to a mirror following acclimation to t he cage. The total number of aggressive displays toward the mirror image wa s greatest when eyespots were masked by green paint. In contrast, black or red artificial eyespots, regardless of size, inhibited biting behavior towa rd the mirror image. The most aggressive males, those who saw a reflected o pponent with no eyespot (hidden with green paint), had significantly higher levels of all plasma catecholamines. These results suggest that A. carolin ensis use information from the eyespot to assess their opponent's readiness to fight and thereby determine whether to be aggressive. Darkened eyespots ape capable of inhibiting aggression, whereas aggressive displays from an opponent in the mirror without darkened eyespots do not. Darkened eyespots reflect rapid changes in plasma PIE, DA, and Epi that may signal dominant s ocial status. (C) 2000 Academic Press.