Comparing interspecific and intraspecific allometry in the Anatidae

Abstract

Interspecific scaling relationships (e.g. of limb size with body mass) in vertebrates are usually assumed to be functional (e.g. biomechanical) attributes. In this paper on the Anatidae, we study the scaling of wing length and tarsus length with body mass, relationships that can be expected to have biomechanical significance. At an interspecific level, both wing length and tarsus are positively allometric, a finding consistent with results from previous comparative avian studies. These trends remained significant in regressions controlling for the effects of phylogeny, but interspecific slopes were less steep within tribes than in the whole family (a taxon-level effect). We are not aware of any biomechanical resasons that explain these patterns satisfactorily. Intraspecific (static) allometries in Green-winged Teal (Anas crecca) and Marbled Teal (Marmaronetta angustirostris) are different: wing length is negatively allometric and tarsus is isometric. These anomalies suggest that interspecific and intraspecific scaling relationships do not share common causes. Our results bring into question the significance of interspecific allometries in vertebrate morphology, which may to some extent be non-functional by-products of morphological optimisation processes within species and ecological differences between them.