The evolution of size of the uropygial gland: mutualistic feather mites and uropygial secretion reduce bacterial loads of eggshells and hatching failures of European birds

Abstract

Potentially, pathogenic bacteria are one of the main infective agents against which a battery of chemical and physical barriers has evolved in animals. Among these are the secretions by the exocrine uropygial gland in birds. The antimicrobial properties of uropygial secretions may prevent colonization and growth of microorganisms on feathers, skin and eggshells. However, uropygial gland secretions also favour the proliferation of feather mites that feed on secretions and microorganisms living on feathers that would otherwise reach eggshells during incubation if not consumed by feather mites. Therefore, at the interspecific level, uropygial gland size (as an index of volume of uropygial secretion) should be positively related to eggshell bacterial load (i.e. the risk of egg infection), whereas eggshell bacterial loads may be negatively related to abundance of feather mites eating bacteria. Here, we explore these previously untested predictions in a comparative framework using information on eggshell bacterial loads, uropygial gland size, diversity and abundance of feather mites and hatching success of 22 species of birds. The size of the uropygial gland was positively related to eggshell bacterial loads (mesophilic bacteria and Enterobacteriaceae), and bird species with higher diversity and abundance of feather mites harboured lower bacterial density on their eggshells (Enterococcus and Staphylococcus), in accordance with the hypothesis. Importantly, eggshell bacterial loads of mesophilic bacteria, Enterococcus and Enterobacteriaceae were negatively associated with hatching success, allowing us to interpret these interspecific relationships in a functional scenario, where both uropygial glands and mutualistic feather mites independently reduce the negative effects of pathogenic bacteria on avian fitness.

Morphology and histology of the uropygial gland in Antarctic birds: relationship with their contact with the aquatic environment?

“…This could explain the fact that both lipids and glycoproteins are secreted along the adenomer. Some of these glycoproteins may have functions related to protection from pathogenic agents (Soler et al 2012). In marine mammals, it has been demonstrated that some cutaneous glands produce glycoproteins with microbicidal action (Meyer et al 2003).…”

“…Its secretion confers water-repellent properties to the feather coat and also maintains the suppleness of the feathers. Other physiological roles of the secretion of the uropygial gland may be associated with pheromone production, control of plumage hygiene, thermal insulation and defence against bacteria and predators Bhattacharyya 1996, 1999;Montalti et al 2006;Salibián and Montalti 2009;Møller et al 2010;Soler et al 2012;Vincze et al 2013).…”

Why do brood parasitic birds lay strong-shelled eggs?

“…Thus there should be strong selection on parasites to develop antimicrobial defences against the bacteria of hosts, while the reverse would not be the case. A thick eggshell is a mechanical defence against microorganisms (Board et al, 1994), and embryo mortality due to microorganisms is common in chicken (Baggott and GraemeCook, 2002) and in many species of wild birds (Soler et al, 2012b). Extensive studies of eggshell strength in chickens have provided evidence for an optimal egg shape with an optimal size and density of eggshell pores (Solomon et al, 1994).…”

Anatomical Changes of Akar Putra Chicken Digestive System after Partial Ablation of Uropygial Gland

“…There are many accepted functions of gland secretions like conferring waterrepellent properties on the feather coat and maintaining the suppleness of it. Furthermore, it's proposed to be associated to pheromone production, control of plumage hygiene, thermal insulation and defense against predators (Jacob, 1992;Montalti et al, 2006;1998;Soler et al, 2012;Vincze et al, 2013). Uropygial gland is completely absent in Struthionidae, Rheidae, Casuaridae, Dromaidae and in a few species of Columbidae and Psittacidae (Johnston, 1988).…”