Analysis of the morphological variation of Doryteuthis sanpaulensis (Cephalopoda: Loliginidae) in Argentinian and Brazilian coastal waters using geometric morphometrics techniques

Abstract

Shape variation of individuals from three locations, two from Argentina and one from Brazil, was analysed by geometric morphometrics techniques. Individuals were weighed, measured, sexed, assigned to a maturity stage and photographed. For the analysis, two landmark configurations were used: one of nine landmarks (9L) and another of 25 landmarks (25L). To visualise shape variation, a principal component analysis (PCA) on Procrustes coordinates was conducted. The percentage of total shape variation explained by the 9L configuration was 80.5% (PC1: 61% and PC2: 19.5%), while the percentage for the 25L configuration was 76.4% (PC1: 54.8% and PC2: 21.6%). Based on this, shape analyses were performed using only the 9L configuration. The PCA results indicated that specimens show a large overlap between the categories based on sex and maturity stage. When location is considered, squid shape from São Sebastião and Rawson Port were very similar, while in Nuevo Gulf, the presence of two different morphological groups were observed: one similar to São Sebastião and Rawson Port, and the other with a morphology typical of Nuevo Gulf. Thus, two different morphotypes were defined: (i) morphotype of the continental shelf and (ii) morphotype typical of the gulf. The continental shelf morphotype is characterised by larger fins and wider mantle than the gulf morphotype. These results suggest that the morphotypes of Doryteuthis sanpaulensis are adaptations to oceanographic regimens.