The uropygial gland of the Eared Dove and its evolutionary history within the Columbiformes (Aves)

Abstract

The uropygial (preen) gland is a holocrine organ unique of Aves. Although several studies have been performed on the uropygial gland of different bird species, knowledge about this gland in Columbiformes is scarce. In order to fill this gap, we analysed in detail the external morphology and the histological and histochemical features of the uropygial gland of the Eared Dove (Zenaida auriculata) in a comparative context. The uropygial gland of the Eared Dove is characterized by its pear-like shape composed of two lobes, conical and naked papilla, tubule-alveolar adenomers, a large primary storage chamber (a feature also present in other terrestrial avian species), and reticular and elastic fibres in the capsule and connective tissue surrounding the adenomers. The histochemistry showed a positive reaction to periodic acid-Schiff, Alcian Blue 2.5 and several lectins, evidencing the presence of diverse glycoconjugates in this organ. Since the uropygial gland may be independently present or absent within Columbiformes, we also used character mapping on a molecular phylogeny to infer the character states of this gland at ancestral nodes to understand its evolutionary history. The analysis shows that the presence of the uropygial gland is the ancestral state for Columbiformes and that its loss occurred more than once independently.