Individual aggressiveness in the crab Chasmagnathus Influence in fight outcome and modulation by serotonin and octopamine

In a previous work we found that size-matched Chasmagnathus crabs establish winner-loser relationships that were stable over successive encounters but no evidence of escalation was revealed through fights Here we evaluated the hypothesis that size-matched fights between these crabs would be resolved according to the contestants level of aggressiveness Moreover we aim at analysing the proximate roots of aggression addressing the influence of the biogenic amines serotonin (5HT) and octopamine (OA) in crab s agonistic behaviour To achieve these purposes the following experiments were carried out First we performed successive fight encounters between the same opponents varying the number of encounters and the Interval between them to assess the stability and progression of the winner-loser relationship Then we analysed dominance relationships in groups of three crabs evaluating the emergence of linearity Thirdly we examined the effects of 5HT and OA injections over the fight dynamics and its result. Our findings show that contest outcome is persistent even through four encounters separated by 24 h but a comparison between encounters does not reveal any saving in fight time or Increase in the opponent disparity Within a group of crabs a rank-order of dominance is revealed which is reflected in their fight dynamics Interestingly these results would not be due to winner or loser effects suggesting that fight outcome could be mainly explained as resulting from differences in the level of aggressiveness of each opponent Moreover this individual aggressiveness can be modulated in opposite directions by the biogenic amines 5HT and OA, being Increased by 5HT and decreased by OA. (C) 2010 Elsevier Inc All rights reserved