David vs. Goliath: XXXX modulates opponent perception between smaller and larger rivals.

@entity3656 @entity238 @entity750 @entity146
UNASSIGNED: During agonistic encounters, the perception of a larger opponent through morphological signaling typically suppresses @entity146 in the smaller individual, preventing contest intensity escalation. However, non-morphological factors such as central @entity750 ( @entity750 ) activity can influence individual @entity146 , potentially altering contest intensity despite initial size discrepancies. When male stalk-eyed flies (Teleopsis dalmanni) fight, contest escalation is directly proportional to similarity in body size, with escalation being lower in size-mismatched contests. We have shown that both high-intensity @entity146 and the probability of winning are increased in males with pharmacologically elevated @entity750 relative to size-matched non-treated opponents. Here, we hypothesized that, in size-mismatched contests, increasing brain @entity750 in the smaller opponent could similarly increase @entity146 and counteract the low contest intensity normally driven by size discrepancy. Size-mismatched male pairs (greater than 5% difference in @entity3656 ) engaged in a forced fight paradigm, with the smaller @entity238 either untreated or with pharmacologically elevated @entity750 levels. The expression of high-intensity aggressive behaviors was significantly increased in smaller treated opponents, but the probability of winning was not altered. This suggests that while elevated serotonergic activity can increase @entity146 and intensity despite perception of a larger opponent, this is not sufficient to overcome size biases with respect to contest outcome. However, the fact that larger opponents continued to win against smaller treated flies was not simply a function of size. Instead, untreated larger males adjusted their fighting strategy to match the increased @entity146 of their smaller treated opponent, suggesting contextual flexibility in behavior based on individual opponent assessment.
