title: Uropygial gland size and composition varies according to experimentally modified microbiome in Great tits.
abstract: BACKGROUND
  Parasites 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.
  
  
  RESULTS
  We 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.
  
  
  CONCLUSIONS
  Birds 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.
authors.affiliation: Laboratoire Évolution et Diversité Biologique (EDB), UMR 5174 Centre National de la Recherche Scientifique (CNRS), Ecole Nationale de Formation Agronomique (ENFA) - Université Paul Sabatier, 118 Route de Narbonne, 31062 Toulouse, France. jacobstaffan@gmail.com.
authors.forename: Staffan
authors.initials: S
authors.lastname: Jacob
authors.forename: Anika
authors.initials: A
authors.lastname: Immer
authors.forename: Sarah
authors.initials: S
authors.lastname: Leclaire
authors.forename: Nathalie
authors.initials: N
authors.lastname: Parthuisot
authors.forename: Christine
authors.initials: C
authors.lastname: Ducamp
authors.forename: Gilles
authors.initials: G
authors.lastname: Espinasse
authors.forename: Philipp
authors.initials: P
authors.lastname: Heeb
mesh_terms: D000818:Animals; D000835:Animals, Wild; D005241:Feathers / Q000382:microbiology*; D005260:Female; D008297:Male; D064307:Microbiota; D009425:Nesting Behavior; D009929:Organ Size; D046109:Passeriformes / Q000033:anatomy & histology / Q000382:microbiology* / Q000502:physiology; D012627:Sebaceous Glands / Q000033:anatomy & histology* / Q000502:physiology*