Predation behaviour of the European squid Loligo vulgaris

Geometric morphometrics casts light on phylogenetic relevance of cephalopod beak morphological

The feeding organ of cephalopod species, the beak, can be used to reveal important ecological information. In this study, geometric morphometric approaches were employed to investigate the phylogenetic relevance and classification effect of beak lateral profile shape. The two-dimensional beak morphologies of 1164 pairs of 24 species from 13 genera and five families were constructed, and their evolutionary relationships and taxonomic status were confirmed using geometric morphometrics and molecular biology approaches. We also assessed the phylogenetic signals of beak shape. The analysis results show shape variation in the beak mainly in the rostrum, hood, and lateral wall. The overall shape parameters (all PCs) of the upper and lower beak are more useful for species identification. The shapes of the upper and lower beak show a strong phylogenetic signal, and the phenogram based on the beak shape basically reflected the families' taxonomic positions. We also hypothesized that the shape variation in the beaks of cephalopods may be ascribed to genetic and environmental differences. In summary, beaks are a reliable material for the classification of cephalopod species. Geometric morphometric approaches are a powerful tool to reveal the identification, phylogenetic relevance and phenotypic diversity of beak shape in cephalopods.

Ontogenetic Variation and Sexual Dimorphism of Beaks among Four Cephalopod Species Based on Geometric Morphometrics

Investigating the ontogenetic variation of biological individuals helps us to fully understand the characteristics of evolution. In order to explore the ontogenetic variation and sexual dimorphism of the beak shape in Octopus minor, Uroteuthis edulis, Sepia esculenta and Sthenoteuthis oualaniensis of the China's coastal waters, the differences between immature and mature stages and the sex-linked differences in the beak shape and size were analyzed with geometric morphometrics methods in this study. The results of Procrustes analysis of variance, principal component analysis and multivariate regression showed that the shapes of the upper beaks of O. minor, U. edulis and S. esculenta differed significantly among various ontogenetic stages (p < 0.05). The shapes of the lower beaks of U. edulis, S. esculenta and Sthenoteuthis oualaniensis were also significantly different among various ontogenetic stages (p < 0.05). The results of thin-plate spline deformation grids showed that the beaks of the four cephalopod species presented different variation patterns. This study gives us basic beak geometry morphology information for Octopus minor, Uroteuthis edulis, Sepia esculenta and Sthenoteuthis oualaniensis present in China's coastal waters. The ontogenetic differences in beak shape might be related to extrinsic factors (diet difference and intra and interspecific competition) in habitat.

Impact of squid predation on juvenile fish survival

Predation is a major source of mortality during the early life stages of marine fishes; however, few studies have demonstrated its impact—especially that of squid predation—on survival processes. Here, we examined the feeding habits and predation impacts of swordtip squid on a major prey fish, juveniles of jack mackerel, in the East China Sea. Otoliths of the juveniles extracted from the squid stomach were used to reconstruct the age–length relationship and the growth trajectory of the consumed juveniles, and they were compared to those of juveniles collected with a net using a newly developed statistical framework. The juveniles consumed by squid had significantly shorter body lengths and smaller body sizes during the late larval and early juvenile stages than the netted juveniles, suggesting that smaller juveniles with slower growth rates have a higher probability to be selected. The body mass ratio of the predator squid to prey juveniles (predator–prey mass ratio, PPMR) ranged from 7 to 700, which was remarkably lower than the PPMR reported in various marine ecosystems based on analyses of fishes. Our findings demonstrate that squid predation can significantly impact the early life survival of fish and the trophodynamics in marine ecosystems.