Looking for ‘identity signatures’ in the American lobster (Homarus americanus): inter-individual variation in body colour and in facial and chelar morphology.

Previous studies have shown that the American lobster, Homarus americanus, is able to recognise the identity of conspecifics. To be recognised, a lobster should bear unique phenotypic traits that are unlikely to be confused in the population. Our aim here was to investigate, in H. americanus, some variable phenotypes that could be good candidates for ‘identity signatures’. Five colour parameters of 44 spots distributed on the body of 12 adult males were measured. We also measured 10 features of the face in 13 adult male lobsters, and 7 and 5 features of the crusher and the cutter chelae, respectively, in 8 of these individuals. Principal Component Analyses showed a clear inter-individual difference in colour patterns and a large variation of facial and chelar morphology. The most variable features were: the shape of the face plus the size and distance between the eyes and the orbital spines; the number, size and shape of the molar-like teeth of the crusher chelae plus the number of its spines; and the size of the dactyl of the cutter chelae plus the number of its incisor-like teeth and spines. Obviously, before concluding that colour and morphological features are identity signatures in H. americanus, behavioural studies and an increased knowledge of visual acuity and colour sensitivity in this species are needed. Nevertheless, the similarity of our results with findings on the crayfish Cherax destructor is intriguing and stimulates further research.