Fighting behaviour and the role of urinary signals in dominance assessment of Norway lobsters, Nephrops norvegicus

Norway lobsters, Nephrops norvegicus, live on the bottom of the continental shelf where they construct and defend burrows. Little is known about their agonistic behaviour and potential mechanisms of dominance. This paper investigates fighting behaviour of size-matched male Norway lobsters with a particular emphasis on the role of urinary chemical signals in the assessment of dominance. Norway lobsters were paired in dyadic encounters on two consecutive days. A decrease in fight duration from first to second encounters indicates that N. norvegicus are able to maintain dominance in sequential contests. The main difference between the two encounters is in the behaviour of the loser. Losers strongly reduce their aggression level from first to second encounters. Olfactory sampling behaviour (antennule flicking) of eventual losers is higher than that of the winner indicating that the loser assesses chemical signals of the dominant male. When urine release is blocked for the second encounter, there is no difference in fight duration between first and second encounter. The results suggest that Norway lobsters develop lasting dominance relationships. The study also provides preliminary evidence that urine-borne chemical signals play an important role in mediating dominance.