Biogenic amines influence aggressiveness in crayfish but not their force or hierarchical rank

Abstract

This study aimed at understanding the influence of biogenic amines on the agonistic behaviour of the crayfish Procambarus clarkii, a model organism for crustacean decapods. Specifically, we investigated whether the hierarchical rank of fighting individuals might be altered by injecting solutions of either serotonin or octopamine into their haemolymph. First, we assessed the effect and duration of the bioamines on the behaviour, posture, and chelar force of 60 adult males paired for size. Then, we examined their potential to modify dominance hierarchies by observing, for 2 h after the treatment, the behaviour of three categories of familiar size-matched pairs: (1) 20 'control pairs' (both individuals injected with a physiological solution), (2) 20 'reinforced pairs' (the dominant individual, alpha, injected with serotonin, and the subordinate individual, beta, with octopamine), and (3) 20 'inverted pairs' (alpha injected with octopamine and beta with serotonin). The results clearly show that the two bioamines were able to alter the posture and aggressiveness of the treated individuals in opposite directions without affecting their chelar force. However, the large majority of the 'inverted pairs' retained their former position in the hierarchy. The role that intrinsic characteristics and prior social experience play in maintaining dominance hierarchies in crayfish is discussed.

Serotonin has opposite effects on the aggressiveness of crayfish, facing either a smaller or a larger rival: alteration of size perception

“…Consequently, the percentage of lost bouts was not significantly increased after 5-HT injection. Conversely, the percentage of wins was not increased in smaller injected crayfish, as previously observed in another study (Tricarico and Gherardi, 2007). In all cases, 5-HT was able to postpone decision making without significantly inverting the outcome of the bouts.…”

“…By contrast, the inverse interpretation generally prevails in crustaceans, as it has been demonstrated that 5-HT increases aggressive motivation and delays the decision to stop fighting (Huber et al, 1997;Huber and Delago, 1998;Herberholz, 2014). However, conflicting observations have also been described in these animals (Peeke et al, 2000;Panksepp et al, 2003;Tricarico and Gherardi, 2007). Moreover, in insects, the effects of 5-HT appear to vary in different species: in crickets, 5-HT is able to decrease aggression and favor escape behavior (Stevenson and Rillich, 2012;Stevenson and Schildberger, 2013), but in ants, aggressiveness is weakly affected by exogenous 5-HT (Szczuka et al, 2013).…”

Aminergic Control of Social Status in Crayfish Agonistic Encounters

“…Despite the effects known of amines on aggressive motivation, the mechanisms underlying winner and loser effects are still poorly understood. In crayfish and crabs, the injection of serotonin or octopamine into dominant and subordinate animals modifies aggressiveness during the following encounters but fails to reverse previous hierarchical rank in [25], [26], [27], [28].…”

Acute fluoxetine exposure alters crab anxiety-like behaviour, but not aggressiveness

“…In the crab Neohelice granulatus (formerly Chasmagnathus ), the level of aggressiveness is a major factor in the outcome of a fight and can be increased with release of serotonin 3 . Serotonin has also been shown to increase aggressive behaviour in lobsters 4 and crayfish 5 , although this does not shift their dominance rank. However, other research has shown a decrease in aggressiveness after serotonin injection in crayfish 6 .…”