Sex differences and prior residence effects in shelter competition in juvenile lobsters, Homarus americanus Milne-Edwards

Using a resident–intruder paradigm, a four-experiment study of competition for a single shelter between same- and mixed-sex dyads of juvenile lobsters, Homarus americanus Milne-Edwards, revealed a significantly greater advantage for male residents than female residents against intruders of either sex. However, there was no significant direct competitive advantage for residents of one sex over intruders of the other, as occurs for adult males over females in this species. There was a prior residence effect only in the male–male dyad condition. Unexpectedly, there was a reliable intruder advantage in female–female dyads. The methods employed showed that the shelter-seeking response of the juvenile lobster is a phylogenetic adaptation and that juvenile aggressive behavior differs little in form from that of adult lobsters but appears to be more intense.