Mechanism analysis of Cephalopod beak pigmentation

Cephalopod beaks, a main feeding structure, is characterized by special formation of pigment. In this study, we analyzed the main chemical composition and carbon-nitrogen stable isotope ratio of whole beaks of three species and different beak parts of Dosidicus gigas with different pigment formation. The results showed that the protein and catechol content in different parts of the beaks were observably different with rostrum>lateral wall>wing, and the C/N ratio is wing>lateral wall>rostrum. The protein and catechol content of three cephalopods were observably different with Sepiella maindroni>D. gigas>Uroteuthis edulis, and the C/N ratio is U. edulis>D. gigas>S. maindroni. There was a significantly positive correlation between chitosan content and the C/N ratio value in different parts of D. gigas’s beak. There was a significantly negative correlation between protein content and C/N value. The C/N of three cephalopods increased with the increasing of chitosan content and the C/N decreased with the increasing of protein content. When the C/N increased, the chitin content was high, the protein content was low and the corresponding pigment became light, while when the C/N decreased, the chitin content was low, the protein content was high and the pigment is dark. Consequently, the degree of pigmentation results from the proportion of protein and chitin, which provides an important basis for investigating specific foraging strategy and individual ontogenetic feeding variation.