Differences in forebrain androgen receptor expression in winners and losers of male anole aggressive interactions

Abstract

Size matched male green anoles (Anolis carolinensis) were paired in a neutral setting and allowed to engage in aggressive displays. Winners and losers were apparent in each pair within 90min, resulting in stable dominant/subordinate dyads. Androgen receptor (AR) expression was assessed at three time points after the initial pairing, 2h, 3 days, and 10 days in dominants, subordinates, and two groups of control males housed alone or with a female for an equal period of time. Expression was quantified in three forebrain areas that have been implicated in aggression and reproductive social behavior in this species, the preoptic area (POA), the anterior hypothalamus (AH), septal area (SEP), and ventromedial nucleus of the posterior division of the dorsal ventricular ridge (PDVRVM ). There were significant overall group differences in AR mRNA expression in the POA and AH that appeared to result from higher POA AR expression in dominant males compared to other groups, and generally lower AR expression in subordinate males. Pairwise comparison revealed that dominants′ AR mRNA expression in the POA was significantly higher in the 2h and 3 day groups compared to that of subordinates, with a similar, but nonsignificant, difference in the 10 day group. Dominants had significantly higher AR mRNA expression in the AH compared to that of subordinates in the 2h group, but differences were not significant at later times. The results suggest that POA and AH sensitivity to androgens is increased in dominants compared to subordinates, and that the difference can be seen soon after the agonistic interaction establishing winners and losers.