A multivariate study of variation in two species of rock crab of the genus Leptograpsus

Abstract

A multivariate approach has been used to study morphological variation in the blue and orange-form species of rock crab of the genus Leptograpsus. Objective criteria for the identification of the two species are established, based on the following characters: width of the frontal region of the carapace; width of the posterior region of the carapace (rear width); length of the carapace along the midline; maximum width of the carapace; and the depth of the body. The first canonical variate, which differentiates between the two species, represents a contrast between the carapace width relative to the width of the front lip and the depth of the body; the blue-form species has a greater relative carapace width than has the orange form. The second canonical variate, which presents a contrast between the rear width and the carapace length, identifies males and females within each species; males have a greater relative carapace length than have females. All individuals, including 20 not used in the study, were correctly identified for colour form. The clear separation of the blue and orange forms achieved by canonical analysis supports the previously determined specific status of the two forms.