Effects of ontogenesis on the morphology of beaks of Sepia esculenta from southern Yellow Sea

Sepia esculenta belongs to Cephalopoda, Sepioidea, Sepiidae, and Sepia, which has become an essential economic seafood species along the northern coast of China. The beak is the main feeding organ of cephalopods, its morphology and internal structure can record biological information on cephalopods at different stages of growth. In addition, there are differences in the feeding objects of cuttlefish at different stages of individual development, which may affect the morphology of beaks. In order to investigate the effects of ontogeny and feeding habits on the beaks of cuttlefish, 138 pairs of beaks of cuttlefish were collected from the southern Yellow Sea from November 2018 to March 2019. Using the landmark point method of geometric morphometry, the upper and lower beaks images were defined and analyzed by 27 marks. The results showed that ① The upper beaks are slightly larger than the lower beaks. And the transition from immature to maturing may be a transgressive period in the growth of the beaks. ② There were significant differences in the size, morphology, and allometric growth pattern of upper and lower beaks in different developmental stages (P<0.05), and there were significant differences in the morphology of upper beaks in different genders (P<0.05), but lower beaks were not the case (P>0.05). ③ The female upper beaks have a high morphological diversity in the mature stage, while the male upper beaks show this in the immature stage. And the maturing stage has a greater influence on the lower beaks. ④ In the immature stage, the beak of cuttlefish was curved and sharp, which facilitated a quick bite on small amphipods. While in maturing stage, the beak’s hood and wing became wider and the beak’s rostrum was sharp, which helped cuttlefish to capture prey precisely of the fast-swimming and agile fish. However, in the mature stage, the beak’s rostrum was short and blunt, the lateral wall was longer and the beak’s wing was wide, which provided a large bite force to crush the hard shell of crustaceans. The development mechanism of beaks at different developmental stages may be a response to better adapt to the changes of feeding objects and satisfy feeding needs. In addition, environmental factors in the southern Yellow Sea may also lead to morphological changes in the beaks of the cuttlefish. Future studies should focus on the internal mechanism of beak deformation in response to the transformation of feeding objects and environmental change. These are associated with individual growth and feeding habit of phenotypic plasticity reflecting the cuttlefish beak growth regularity and the adaptive use of food resources of cuttlefish. This study, through the analysis of the growth of cuttlefish’s beak shape change, improved the basic biology of cuttlefish information, and may provide a certain scientific basis for reasonable use of resources.