Abstract
Cannibalism, the consumption of one's own species, is observed in many crustacean species, with understanding of the interactions between physiological and behavioural drivers ever evolving. Spiny lobsters opportunistically cannibalise deceased conspecifics and attack and cannibalise live individuals in culture. High incidence of cannibalism is observed in juvenile communal culture of the tropical rock lobster Panulirus ornatus. Understanding the behavioural and chemosensory context of cannibalism has revealed an opportunity to identify the chemical cues released by moulting lobsters, as their vulnerable physical condition makes them ideal victims. Behavioural choice assays revealed that juvenile lobsters are not attracted to inter-moult conditioned water, or haemolymph from inter-moult or pre-moult juvenile lobsters. However, lobsters were consistently attracted to water conditioned by moulting conspecifics, demonstrating attraction to chemical cues released into the aquatic environment during moulting. Juvenile lobsters were attracted to N-acetylglucosamine-6-phosphate (GlcNAc-6-P, 0.5 mg l-1), a metabolite in the chitin biosynthesis pathway. Lobsters spent an average 90% of their exposure time within moult-conditioned water and GlcNAc-6-P currents in a two-current choice flume behavioural assay. Using ion chromatography coupled with mass spectrometry, GlcNAc-6-P was detected in the moult fluid of pre-moult juvenile lobsters. These findings indicate that cannibals may identify pre-moult victims through chemical cues present in the moult fluid, such as GlcNAc-6-P. This is a novel investigation for P. ornatus, broadening our understanding of the physiological and ecological mechanisms mediating cannibalism. Highlighting this important chemical and behavioural link in juvenile cannibalism may provide a chemical option for mitigating cannibalism in crustacean culture.