Title

Perception of the steroid hormone 20-hydroxyecdysone modulates agonistic interactions in Homarus americanus

Document Type

Article

Date of Original Version

6-1-2008

Abstract

The American lobster, Homarus americanus, becomes more aggressive just before moulting. This increased aggression is accompanied by an increase in the blood and urine titres of the moulting hormone, 20-hydroxyecdysone (20-HE). During combats with conspecifics, lobsters urinate upon each other to signal their aggressive and/or sexual status. We videotaped staged combats between large intermoult nongravid female lobsters exposed to 20-HE, α-ecdysone or artificial sea water (ASW) and small nongravid female lobsters that could not smell. The nephropores of both combatants were plugged to prevent urine-release. Aggressive, defensive and avoidance behaviours were ranked according to aggressiveness in a rank of aggression hierarchy, which included opponent-directed and (nonopponent) redirected behaviours. Exposure to 20-HE increased the state of arousal of large lobsters: they performed more highly aggressive behaviours, more defensive and more avoidance behaviours than either α-ecdysone-exposed or ASW-exposed lobsters. The small opponents of large 20-HE-exposed lobsters performed more aggressive behaviours. The summed aggressive intensity of all behaviours of both lobsters in a fight was greater in 20-HE fights than in ASW or α-ecdysone fights. The difference in aggressive intensity of all behaviours between the 20-HE-exposed lobsters and their opponents was significantly smaller in 20-HE fights than in α-ecdysone or ASW fights. Our results indicate that 20-HE exposure alters the agonistic behaviour of a lobster, which then evokes an increase in the aggressive behaviour of an opponent lobster. The findings suggest that 20-HE acts as a pheromone modulating aggressive interactions in lobsters. © 2008 The Association for the Study of Animal Behaviour.

Publication Title

Animal Behaviour

Volume

75

Issue

6

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