| Cephalopods belong to Mollusca and are widely distributed in the oceans and coastal waters of various countries in the world.More than 800 extant species have been identified.As a short-lived species,the role of cephalopods in the ecosystem is complex.As the main feeding organ of cephalopods,beak is a hard tissue structure,which has stable structure and is resistant to corrosion.Therefore,it is widely used in morphology research.At present,there are multiple landmark schemes for the geometric analysis of beaks,and it is unknown how many samples and landmarks are enough to describe the changes in the shape and size of beaks.The current cephalopod species are widely distributed in different habitats of the world’s oceans,and the differences in habitat and feeding habits of cephalopods may lead to the morphological evolution of beaks,so the cephalopod beaks show morphological diversity.Although the effectiveness of beak morphology in species classification and population identification has been confirmed,there is a lack of studies on individual growth changes,phylogenetic correlation,ecomorphology and functional morphology of beak geometry morphology in different cephalopod species.For this purpose,a total of 45 cephalopod species in 30 genera of 14 families,4suborders were sampled,and two-dimensional images of 1344 upper beak and 1395 lower beak lateral profiles were obtained.Firstly,different sample and landmarks schemes were designed based on previous research,and the optimal sample size and landmarks scheme for the study of beak morphology in four suborders were determined.Then,the ontogenetic stages of four suborder cephalopod species were divided,and the geometric morphometrics method was used to explore the growth and development changes of beak morphology.Then,combined with molecular biology data,the phylogenetic signal and evolution rate of beak morphology were analyzed,and a hierarchical clustering analysis,(HCA)tree based on morphological data was constructed to explore the classification effect and evolution process of beak morphology.Finally,combined with the ecological data and functional data of cephalopod species,the ecological significance of the morphological difference of beak was explored.This study helps us to understand the variations in the morphological structure of the beak,and explore the relationship between the function and morphology of the beak of different phylogenetic and ecological groups.It provides scientific basis for the sustainable development and utilization of offshore and oceanic cephalopod resources in China,a more comprehensive understanding of the life cycle characteristics of cephalopods,and a reference for related research on other biological groups.The results are as follows:(1)Standard for landmarks selection of beak morphological among four suborder cephalopods.Beak samples and lateral profiles images of representative species Sepia esculenta,Uroteuthis edulis,Sthenoteuthis oualaniensis,and Octopus minor of four suborders were obtained for landmark sampling evaluation curve analysis.The results showed that the difference in the number of landmarks may lead to errors in the centroid size of the beak.In order to best show the degree of morphological variation of the beak(F = 0.99),comprehensively considering different cephalopod species,27 landmarks were used in the upper and lower beak when the beak sample were about 50-80 pairs.When the sample was 80 ～ 300 pairs in the group,28 landmarks were used,and finally the best landmarks scheme for the morphological variation of beak was definitely represented by the vector map of beak morphology.(2)Individual growth variation in the morphology of beaks among four suborder cephalopods.Geometric morphometric analysis of beaks at different developmental stages representative species of four suborders Sepia esculenta,Uroteuthis edulis,Sthenoteuthis oualaniensis,Octopus minor.The results showed that there were significant differences in the morphology of the beaks of Sepia esculenta,Uroteuthis edulis,Sthenoteuthis oualaniensis,Octopus minor(P < 0.01),and the hood,wings and rostral of the upper and lower beaks underwent variation.There are sexual dimorphisms and allometry in the growth process of beaks,and there are certain differences in the growth and development process of beak morphology of different species,which may be different in the function and development mechanism of beaks of the cephalopod species.Multivariate regression tree analysis found that there was a certain correlation between feeding preference and the growth variation of beak shape,and the growth variation of beak of various species was a manifestation of its adaptation to complex marine environment,reflecting the adaptability of cephalopod species to feeding resources,which is also one of the manifestations of the phenotypic plasticity of cephalopod.(3)Taxonomic and phylogenetic in the morphology of beaks of beaks among four suborder cephalopods.The morphological differences of 1344 upper beaks and 1395 lower beaks of 45 cephalopod species in 30 genera of 14 families,4 suborders 4 suborders were analyzed under the phylogenetic context,the classification effect of beak morphology,the characteristics and differentiation characteristics of morphological differences between species were evaluated,and the phylogenetic signal and evolution rate of beak morphology were quantitatively tested.The results showed that there were significant differences in the size and shape of beaks of different suborders and species(P < 0.01),and the overall shape of the upper and lower beaks had better effect on the classification of suborders and species.A Kmult test for the upper and lower beaks shows that beak shape has a moderate but significant phylogenetic signal(K = 0.399,P < 0.01;K = 0.386,P < 0.01),there was a significant difference in the rate of morphological evolution of different species of beaks(P < 0.01).Beaks are reliable material for the classification of cephalopods at the suborder and species level,and differences in habitat,predation mechanisms,and food resources may have contributed to the evolution of the shape of the beak,which is the result of a combination of genetic and environmental differences.(4)Ecomorphology and functional morphology of beaks among four suborder cephalopods.By collecting and calculating the ecological and functional data of 45 cephalopod species,the morphological differences of different feeding ecology,habitat and function were analyzed on the basis of the phylogenetic factors for removal of the morphological changes of the beak,and the ecological and functional signals of the beak were evaluated.The results show that there is a certain correlation between beak morphology and feeding ecology,habitat environment and beak function,and beak morphology shows certain ecological and functional signals.Therefore,it is speculated that the evolution of beak morphology is compatible with feeding,habitat and functional types,and different habitats may be the reason for promoting the convergent evolution of beak shape,and at the same time evolve different feeding,ecological and functional types. |
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