The uropygial gland of the monk parakeet Myiopsitta monachus: Histology, morphogenesis, and evolution within Psittaciformes (Aves)

Abstract

We describe the morphology, histology, and histochemical characteristics of the uropygial gland (UG) of the monk parakeet Myiopsitta monachus. The UG has a heart-shape external appearance and adenomers extensively branched with a convoluted path, covered by a stratified epithelium formed by different cellular strata and divided into three zones (based on the epithelial height and lumen width), a cylindrical papilla with an internal structure of delicate type and two excretory pores surrounded by a feather tuft. Histochemical and lectinhistochemical techniques performed showed positivity against PAS, AB pH 2.5, AB-PAS, and some lectines, likely related to the granivorous feeding habits.Also, we describe the morphogenesis of the UG of the monk parakeet, which appears at embryological stage 34 as a pair of ectodermal invaginations.Heterochronic events in the onset development of the UG when compared with other birds could be recognized. Finally, to examine the phylogenetic occurrence of the UG within the Psittaciformes and infer its evolutionary history, we mapped its presence/absence over a molecular phylogeny. The reconstruction of the characters states at ancestral nodes revealed that the presence of the UG was the plesiomorphic feature for Psittaciformes and its loss evolved independently more than once. K E Y W O R D Sancestral state reconstruction, evo-devo, heterochrony, histochemistry

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

“…It is well known that the UG varies in shape and size among species and sometimes among closely related ones (e.g. in Psittaciformes, Carril et al, 2019). When comparing our results with the information available for other Podicipediformes, the UG of the Hooded Grebe is very similar to that of other grebe species (Jacob & Ziswiler, 1982;Johnston, 1988).…”

“…The histochemical and lectin-histochemistry analyses of the UG of the Hooded Grebe revealed the presence of a few carbohydrates as part of GCs (glycolipids and glycoproteins) identified by PAS technique and the presence of GCs with carboxyl groups and/or sulphated esters by AB 2.5 reaction. Recent studies showed similar results for other bird species (Carril et al, 2019;Chiale et al, 2015Chiale et al, , 2016Chiale et al, , 2019Shaffian & Mobini, 2014). It has been demonstrated that these GC varieties have protective functions against microorganisms in several fish species (Díaz et al, 2008;Esteban, 2012;Yashpal et al, 2014).…”

“…Another aspect of the UG of the Hooded Grebe is the presence of elastic fibres. Although some studies did not find these fibres as components of the connective tissue of this gland (Hou 1928), many others found them in terrestrial and aquatic species (Carril et al, 2019;Chiale et al, 2015;Chiale et al, 2016;Chiale et al, 2019;Jacob & Ziswiler, 1982). The function of these fibres could be related to a change of volume in this organ.…”

“…At the histological level, the UG is a holocrine organ surrounded by a capsule of dense connective tissue from which the intermedial septum and thin branches that surround the adenomers originate (Reynolds et al, 2017). Apart from collagen fibres, the capsule and the intermedial septum also have reticular and elastic fibres, while the connective tissue around the adenomers is principally formed by reticular fibres (Carril et al, 2019;Chiale et al, 2014;Chiale et al, 2015;Chiale et al, 2016;Chiale et al, 2019). The lobes have tubular or tubuloalveolar adenomers with a stratified epithelium formed of four different strata: basal or germinative intermediate, secretory and degenerative (Jacob & Ziswiler, 1982;Lucas & Stettenheim, 1972).…”

“…Birds that feed on carrion (e.g. Chimango Caracara (Milvago chimango) and Southern Caracara (Caracara plancus) displayed a positive reaction to many lectins (Chiale et al, 2015;Chiale et al, 2016, respectively) while seed-eating birds such as the Eared Dove (Zenaida auriculata) (Chiale et al, 2019) and the Monk Parakeet (Myiopsitta monachus) (Carril et al, 2019) showed a positive reaction to only a few of the lectins performed, indicating a lower variety of glycoconjugates.…”