Uropygial gland size and composition varies according to experimentally modified microbiome in Great tits

Abstract

BackgroundParasites exert important selective pressures on host life history traits. In birds, feathers are inhabited by numerous microorganisms, some of them being able to degrade feathers or lead to infections. Preening feathers with secretions of the uropygial gland has been found to act as an antimicrobial defence mechanism, expected to regulate feather microbial communities and thus limit feather abrasion and infections. Here, we used an experimental approach to test whether Great tits (Parus major) modify their investment in the uropygial gland in response to differences in environmental microorganisms.ResultsWe found that males, but not females, modified the size of their gland when exposed to higher bacterial densities on feathers. We also identified 16 wax esters in the uropygial gland secretions. The relative abundance of some of these esters changed in males and females, while the relative abundance of others changed only in females when exposed to greater bacterial loads on feathers.ConclusionBirds live in a bacterial world composed of commensal and pathogenic microorganisms. This study provides the first experimental evidence for modifications of investment in the defensive trait that is the uropygial gland in response to environmental microorganisms in a wild bird.

Is oxidative status influenced by dietary carotenoid and physical activity after moult in the great tit (Parus major)?

“…For example, when preen oil was removed from feathers of Bohemian waxwings (Bombycilla garrulus), UV chroma increased, suggesting a direct effect of preen oil on structural colour (Pérez-Rodríguez et al, 2011). Feather plucking may thus have modified uropygial gland function and/or induced an infection, as feather mite and microbiome abundance have been shown to influence uropygial gland size and function (Galván and Sanz, 2006;Jacob et al, 2014), and handicapped males showed higher blood sedimentation rate. However, the effect of the handicap treatment on UV chroma was similar in females and males, though the former showed no parallel effect on blood sedimentation.…”

“…Mechanisms underlying seasonal variation in coloration are not yet well understood, but some hypotheses have been advanced, such as UV bleaching, and bacterial or mechanical degradation (Delhey et al, 2010). In great tits, the brightness of the yellow coloration has been shown to increase with the size of the uropygial gland (Galván and Sanz, 2006), which produces an oil that birds deposit on their feathers, its size and oil composition varying with microbiome composition (Jacob et al, 2014). Moreover, activation of the immune system may induce changes in antioxidant status.…”

Do feather-degrading bacteria actually degrade feather colour? No significant effects of plumage microbiome modifications on feather colouration in wild great tits

“…We randomly assigned the nests to three treatments as presented in Jacob et al (2014). First, to favour the bacterial growth in the nests, we used TSB (tryptic soy broth, 40 mg/ L in sterilized distilled water, Sigma), a liquid general growth medium for heterotrophic microorganisms that is commonly used in microbiology.…”

“…By spraying different solutions into randomly allocated nests, we either favoured or inhibited bacterial growth in active nests during the breeding season (Jacob et al 2014). These treatments led to modifications of both total and keratinolytic cultivable bacterial densities in the nests and, by contamination through contact between birds and their nests, also modified adult feather bacterial loads (Jacob et al 2014). We first tested the hypothesis that bacterial keratinolytic activity on feathers alters colouration in free-living great tits.…”

“…Finally, males and females have often been found to differ in their exposure to nest microorganisms and reproductive strategies (Gosler 1993;Saag et al 2011;Kilgas et al 2012b). Females are expected to be more exposed to nest microorganisms and to harbour higher bacterial loads on feathers (Saag et al 2011;Jacob et al 2014), and consequently might experience more pronounced effects of the treatments. We thus investigated whether treatment effects differed between sexes by testing for the treatment by sex interaction on feather colouration.…”