Comparative morphology and histochemistry of the uropygial gland of the endangered and endemic Hooded Grebe (Podiceps gallardoi, Podicipediformes)

Abstract

The Hooded Grebe is an endangered and endemic species of Podicipediformes of Argentina. Many aspects of this bird's biology are still unknown including the uropygial gland. This is the first morphological and histochemical description of the uropygial gland for this species in a comparative context. The uropygial gland of these birds had parallel arranged lobes with a kidney-like shape, a conical papilla and a feather tuft in a sub-terminal position. The lobes were composed of tubular adenomers with a straight course that lead to secondary chambers. The capsule and connective tissue around the adenomers had elastic fibres. It showed a positive reaction to AlcianBlue/Periodic Acid Schiff and several lectins indicating the presence of glycoconjugates. The uropygial gland of the Hooded Grebe shares morphological characteristics with other aquatic species (e.g. secondary chambers) and the presence of glycoconjugates might suggest protective functions against microbes as previously proposed. The sub-terminal position of the feather tuft is a unique characteristic of this species indicating that this position leaves the tuft in a dorsal location and could be involved in parent-chick recognition mediated by odour transmission.Further studies are needed to increase our knowledge on some behavioural aspects of this species related to the biochemical composition of the uropygial secretion.

The uropygial gland of the Great Cormorant (Phalacrocorax carbo): I. Morphology

“…These zones differ in the thickness and shape of their subdivisions, i.e., the stratum germinativum, the intermediate, the degenerative, and the secretory layers. The main histological differences between species seem to be related to the presence or absence of central storage chambers which are mostly present in purely terrestrial birds as eared doves (Chiale et al 2019), rock pigeon (this study, Hassanin et al 2021, (Chiale et al 2016(Chiale et al , 2017, kiwi (Reynolds et al 2017), and monk parakeet (Carril et al 2020) but absent in most aquatic birds as the hooded grebe (Chiale et al 2022), duck (Hassanin et al 2021, penguins (Chiale et al 2014) and cormorant (this study). Thus, aquatic birds continuously in need of uropygial secretions for feather maintenance seem to release the secretions constantly whereas terrestrial birds secrete only periodically and therefore have to store the secretions until need.…”

“…More recently, the uropygial glands of a number of species some of which had already been examined by Jakob and Ziswiler (1982) have been described in some detail, e.g., moorhen (Sawad 2006), white stork (Kozlu et al 2011), goose (Shafiian andMobini 2014), duck (Hassanin et al 2021), hooded grebe (Chiale et al 2022), caracara (Chiale et al 2016(Chiale et al , 2017, kiwi (Reynolds et al 2017), eared dove (Chiale et al 2019), rock pigeon (Hassanin et al 2021; this study), and monk parakeet (Carril et al 2020). The general histological structure of the gland is similar in all birds investigated so far, including the Great Cormorant examined in the present study.…”