Morphology of the brown tree snake, Boiga irregularis, with a comparison of native and extralimital populations

Abstract

We conducted an analysis of the morphology of specimens of the brown tree snake, Boiga irregularis, from the native range of eastern and northern Australia, Papua New Guinea and the Solomon Islands. First, a cluster analysis was conducted to determine natural groupings in the data; however, no groupings based on morphological characters were found. Then the importance of additional factors such as geographical groupings and coloration was analysed in a nonparametric analysis of variance. Significant differences were found in the mean rankings of key characters such as dorsal mid-body, ventral and subcaudal scale counts. However, the amount of variation and the degree of overlap among populations and groupings precluded separating animals on the basis of these features. Our data support the recognition of a single species with two subspecies based on colour variation. We also compared the morphology of a sample of brown tree snakes from an extralimital population on Guam to that of this species in the areas of the native range. Our data supported suggestions of alliances of the Guam population with northern Papuan populations. However, the Guam population of the brown tree snake was found to be less variable than were localised natural populations. Morphologically, the Guam population is distinctive, suggesting that it has undergone significant morphological change since its introduction.