Variation in Assemblages of Feather Bacteria in Relation to Plumage Color in Female Great Tits

Abstract

Abstract. Microorganisms are known to play an important role in shaping the life histories of animals. Recent studies have proposed that the coloration of birds' plumage could reflect individual quality through associations with feather-degrading bacteria. however, few studies have explored such relationships. We studied breeding female great Tits (Parus major) during nest building and chick rearing to explore associations between bacteria inhabiting their yellow chest feathers and feather coloration. Specifically, we used flow cytometry and ribosomal intergenic spacer analysis (RISA), respectively, to study the densities of all free-living and attached bacteria and the phylotypic richness of feather-degrading bacterial assemblages. We used chroma (color saturation) as a measure of feather coloration. During chick rearing but not during nest building, the female's chroma was negatively related to the phylotypic richness of feather-degrading bacteria. Also, a seasonal change in the density of attached bacteria associating with individual birds was negatively associated with change in chroma over the same period. These findings suggest that conspicuous coloration of female great Tits may reflect the numbers and character of bacteria inhabiting feathers.Key words: carotenoid-based coloration, chroma, feather-degrading bacteria, female coloration, Parus major.Variación en el Ensamble de bacterias de las Plumas con Relación al Color del Plumaje de la hembra de Parus majorResumen. Se sabe que los microorganismos juegan un rol importante en modelar las historias de vida de los animales. Estudios recientes han propuesto que la coloración del plumaje de las aves podría reflejar la calidad individual indicando la asociación con bacterias que degradan las plumas. Sin embargo, pocos estudios han explorado estas relaciones. Estudiamos hembras reproductivas de Parus major durante la construcción del nido y la cría de pichones para explorar asociaciones entre bacterias que habitan sus plumas amarillas del pecho y la coloración de las plumas. Específicamente, usamos citometría de flujo y análisis ribosomal de espaciadores intergénicos (RISA por sus siglas en Inglés), respectivamente, para estudiar las densidades de todas las bacterias libres y ligadas y la riqueza filotípica de los ensambles de bacterias que degradan las plumas. Empleamos croma (saturación del color) como una medida de coloración de la pluma. Durante la cría de los pichones pero no durante la construcción del nido, la croma de la hembra estuvo negativamente relacionada a la riqueza filotípica de las bacterias que degradan las plumas. Además, el cambio estacional en la densidad de las bacterias ligadas asociadas con aves individuales estuvo negativamente asociado con los cambios en la croma a lo largo del mismo período. Estos resultados sugieren que la coloración conspicua de las hembras de P. major puede reflejar la cantidad y el carácter de las bacterias que habitan las plumas.

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

“…Earlier studies have suggested that feather microorganisms could play a role in the evolution of feather colouration (Shawkey et al 2007;Shawkey et al 2009;Gunderson et al 2009;Kilgas et al 2012a). However, experimental evidence on free-living birds is still lacking to support this hypothesis (Clayton 1999;Cristol et al 2005;Gunderson 2008).…”

“…Moreover, carotenoid pigments invested in feather colouration are no longer available for immune system functioning (Olson & Owens 1998;Aguilera & Amat 2007; but see Navara & Hill 2003). If bacteria present on feathers interact with the host immune function, an allocation trade-off between immune response and feather colouration would lead to negative correlations between feather bacterial densities and components of plumage colouration as found in previous studies (Shawkey et al 2009;Gunderson et al 2009;Kilgas et al 2012a).…”

“…For the yellow breast and green back, we calculated yellow chroma as the proportion of reflectance between 515 and 700 nm compared to total reflectance between 420 and 700 nm, indicative of the influence of light absorbance by feather carotenoids. Yellow chroma is involved in sexual selection in great tits by revealing body condition (Senar et al 2008) and has been found correlated to feather bacteria (Kilgas et al 2012a), and both brightness and UV chroma are modified during in vitro degradation of feathers by keratinolytic bacteria (Shawkey et al 2007). …”

“…In contrast, carotenoid-based plumage colouration in house finches (Carpodacus mexicanus) and plumage brightness in female bluebirds were found to be negatively correlated to the densities of feather-degrading bacteria (Shawkey et al 2009;Gunderson et al 2009). Feather colour saturation was also found to be negatively correlated to the number of bacterial species on female great tit feathers (Kilgas et al 2012a). These correlational studies suggest that feather microorganisms can degrade feather keratin in vivo and consequently alter feather colouration, as found with in vitro experiments (Shawkey et al 2007;Gunderson 2008).…”

“…An alternative hypothesis to explain the negative correlations found between colouration and feather microorganisms (Shawkey et al 2007;Shawkey et al 2009;Kilgas et al 2012a) is that birds could modify their investment in feather colouration during moult depending on their exposure to microorganisms. During moult, birds face trade-offs between producing new feathers and maintaining thermoregulation, flight and immune functions (Vézina et al 2009;MorenoRueda 2010).…”