Sexual shape dimorphism in the skull of the hooded seal Cystophora cristata

Abstract

Multiple-group principal component analysis was used to investigate morphological differences between skulls of male and female hooded seals. The scores on the first principal axis (PCI), calculated from the variance-covariance matrix of log-transformed data, were highly correlated with age and the component was interpreted as a general growth axis. The other components had correlations between dimensions and component scores of different signs and magnitude and were interpreted as shape axes. The standardized component scores were subjected to analyses of variance and discriminant analyses. Sexual dimorphism was disclosed on eight of the components including PCI, and was functionally related mostly to the hood of the males.