Comparing interspecific and intraspecific allometry in the Anatidae

Interspecific scaling relationships (e. g. of limb size with body mass) in vertebrates are usually assumed to be functional (e. g. biomechanical) attr ibutes. 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 hav e biomechanical significance. At an interspecific level, both wing length a nd tarsus are positively allometric, a finding consistent with results from previous comparative avian studies. These trends remained significant in r egressions controlling for the effects of phylogeny, but interspecific slop es were less steep within tribes than in the whole family (a taxon-level ef fect). We are not aware of any biomechanical resaons that explain these pat terns satisfactorily. Intraspecific (static) allometries in Green-winged Te al (Anas crecca) and Marbled Teal (Marmaronetta angustirostris) are differe nt: wing length is negatively allometric and tarsus is isometric. These ano malies suggest that interspecific and intraspecific scaling relationships d o not share common causes. Our results bring into question the significance of interspecific allometries in vertebrate morphology, which may to some e xtent be non-functional by-products of morphological optimisation processes within species and ecological differences between them.