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

SILVIA PEDETTA; LAURA KACZER; HECTOR MALDONADO

PHYSIOLOGY AND BEHAVIOR

PERGAMON-ELSEVIER SCIENCE LTD

Año: 2010

0031-9384

In a previous work we found that size-matched Chasmagnathus crabs establish winner-loserrelationships that were stable over successive encounters but no evidence of escalation was revealedthrough fights. Here, we evaluated the hypothesis that size-matched fights between these crabs wouldbe resolved according to the contestants´ level of aggressiveness. Moreover, we aim at analysing theproximate roots of aggression, addressing the influence of the biogenic amines serotonin (5HT) andoctopamine (OA) in crab´s agonistic behaviour. To achieve these purposes, the following experimentswere 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 andprogression of the winner-loser relationship. Then, we analysed dominance relationships in groups ofthree crabs, evaluating the emergence of linearity. Thirdly, we examined the effects of 5HT and OAinjections over the fight dynamics and its result. Our findings show that contest outcome is persistenteven through four encounters separated by 24 h, but a comparison between encounters does notreveal any saving in fight time or increase in the opponents disparity. Within a group of crabs, a rankorderof dominance is revealed which is reflected in their fight dynamics. Interestingly, these resultswould not be due to winner or loser effects, suggesting that fight outcome could be mainly explained asresulting from differences in the level of aggressiveness of each opponent. Moreover, this individualaggressiveness can be modulated in opposite directions by the biogenic amines 5HT and OA, beingincreased by 5HT and decreased by OA.