Geographical variation in the morphology of the Wedge-tailed Shearwater (Puffinus pacificus)

Abstract

Geographical variation in the morphology of the Wedge-tailed Shearwater (Puffinus pacificus) was assessed using multivariate analyses, including MANOVA and canonical discriminant analysis. This study tested the roles of climatic (sea surface temperature) and geographical (latitude, longitude and inter-population distance) factors as potential agents of natural selection on the body dimensions of this geographically variable species. Patterns of morphological variation, represented by phenotypic distances, were found to be unrelated to the geographical proximity of colonies. The Wedge-tailed Shearwater exhibited the trend in body size predicted by Bergmann's Rule, increasing significantly with increasing latitude and decreasing temperature. Allen's Rule proposes that an animal's extremities should be relatively shorter in colder climates, but the data did not support this hypothesis with regards to variation in bill-shape of the Wedge-tailed Shearwater. Owing to the interrelated nature of ecological parameters, such as food, climate, distribution, life history and breeding biology, it is unlikely that a single factor is responsible for the observed morphological variation. However, food, through its influence on competition, dispersal, growth, fecundity and survival, may play an important role in the patterns of morphological variation found in this study. Therefore, the heterogeneity of the foraging habitat over the range of the species may be responsible for the observed variation, owing to differences in the distance required to travel to the feeding grounds and the availability and quality of food.