Bacteria as an Agent for Change in Structural Plumage Color: Correlational and Experimental Evidence (original) (raw)
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Journal of Avian Biology, 2009
Parasites influence the expression of secondary sexual traits and the health of infected individuals. We set out to test the influence of reputed exogenous parasites, plumage bacteria, including feather-degrading bacteria (FDB), on secondary sexual characteristics and body condition of wild adult eastern bluebirds Sialia sialis. Previous work has shown that FDB alter the coloration of structurally-colored bluebird feathers in vitro ). In a correlational study of how bacteria affect birds in the wild, we found that female plumage got duller with increasing FDB intensity. Males tended to get brighter with increasing FDB intensity, but the relationship was not significant. We also found significant associations between plumage bacteria intensity and body condition, but, again, with gender-based differences. Female body condition was negatively associated with plumage bacteria intensity, while male body condition was positively associated with plumage bacteria intensity. Interestingly, plumage bacteria intensity of males and females in nesting pairs was significantly positively correlated. We also report the highest prevalence of FDB measured in a wild bird population, with FDB detected on 67/68 (99%) of individuals. Further work is needed to fully understand the relationships between plumage bacteria and birds, but our data indicate that plumage bacteria may have sex-dependent effects on multiple phenotypic traits.
Naturwissenschaften, 2014
Parasites are known to exert selective pressures on host life history traits since the energy and nutrients needed to mount an immune response are no longer available to invest in other functions. Bird feathers harbour numerous microorganisms, some of which are able to degrade feather keratin (keratinolytic microorganisms) and affect feather integrity and colouration in vitro. Although named "feather-degrading" microorganisms, experimental evidence for their effects on feathers of free-living birds is still lacking. Here, we tested whether (i) keratinolytic microorganisms can degrade feathers in vivo and thus modify the colour of feathers during the nesting period and (ii) whether feather microorganisms have a long-term effect on the investment in colouration of newly moulted feathers. We designed treatments to either favour or inhibit bacterial growth, thus experimentally modifying plumage bacterial communities, in a wild breeding population of great tits (Parus major). Our analyses revealed no significant effects of the treatments on feather colours. Moreover, we found that differences in bacterial exposure during nesting did not significantly affect the colouration of newly moulted feathers. Our results suggest that significant feather degradation obtained during in vitro studies could have led to an overestimation of the potential of keratinolytic microorganisms to shape feather colouration in free-living birds.
Do feather-degrading bacteria affect sexually selected plumage color?
Naturwissenschaften, 2009
Models of parasite-mediated sexual selection propose that males with more elaborate sexual traits will have fewer parasites. These models have generally been tested using metazoan or protozoan parasites of the blood, gut, or integument. Fewer studies have examined sexual ornaments in relation to bacterial infections. While most surface bacteria are harmless or beneficial, feather-degrading bacteria may have detrimental effects. In this study, we examined the relationships between overall bacterial load, feather-degrading bacterial load, and sexually selected carotenoid-based plumage color in a wild population of house finches (Carpodacus mexicanus). We found that males with the redder plumage preferred by females had similar overall bacterial loads, but lower feather-degrading bacterial loads, than males with less red plumage. These data suggest that plumage color can signal abundance of feather-degrading bacteria to potential mates. It remains unclear whether feather-degrading bacteria directly or indirectly affect plumage color, but the observed correlations suggest that feather-degrading bacteria may play some role in sexual selection.
Microbial Ecology, 2011
Microorganisms have been shown to play an important role in shaping the life histories of animals, and it has recently been suggested that feather-degrading bacteria influence the trade-off between parental effort and self-preening behavior in birds. We studied a wild breeding population of great tits (Parus major) to explore habitat-, seasonal-, and sex-related variation in feather-degrading and free-living bacteria inhabiting the birds' yellow ventral feathers and to investigate associations with body condition. The density and species richness of bacterial assemblages was studied using flow cytometry and ribosomal intergenic spacer analysis. The density of studied bacteria declined between the nest-building period and the first brood. The number of bacterial phylotypes per bird was higher in coniferous habitat, while bacterial densities were higher in deciduous habitat. Free-living bacterial density was positively correlated with female mass; conversely, there was a negative correlation between attached bacterial density and female mass during the period of peak reproductive effort. Bacterial species richness was sex dependent, with more diverse bacterial assemblages present on males than females. Thus, this study revealed that bacterial assemblages on the feathers of breeding birds are affected both by life history and ecological factors and are related to body condition.
Resistance of melanized feathers to bacterial degradation: is it really so black and white?
Journal of Avian Biology, 2008
Melanins are common feather pigments that contribute to signaling and crypsis. Melanins may also help feathers resist feather-degrading bacteria (FDB). Two recent studies ) tested the resistance of melanized versus unmelanized feathers to FDB using in vitro experiments, but draw opposite conclusions. concluded that melanized feathers resist FDB more than unmelanized feathers, while concluded that unmelanized feathers resist FDB more than melanized feathers. To resolve this conflict in the literature, we replicated previous studies but included additional tests not previously used. We inoculated melanized and unmelanized feathers of domestic geese Anser anser domesticus, with the FDB Bacillus licheniformis and measured bacterial activity every two days over two weeks. Three metrics of bacterial activity on feathers were measured: soluble protein content around feathers in solution, bacterial growth on feathers, and loss of feather mass. The latter two metrics were not considered in the aforementioned studies, which indirectly measured bacterial activity. We conducted two trials, one in which feathers were sterilized by autoclaving before inoculation , and a second in which feathers were sterilized by ethylene oxide gas. This allowed us to test whether autoclaving, done in previous studies, influences bacterial activity on feathers and could confound results. In both trials, unmelanized feathers degraded earlier, supported greater bacterial growth, and lost more mass than melanized feathers. These results support the findings of ; melanized feathers are more resistant to FDB than unmelanized feathers. Thus, using direct metrics of bacterial activity, we resolve a current conflict in the literature. We also found that autoclaving feathers influences FDB activity on them, and thus autoclaving should be avoided in future studies.
Ibis, 2010
The Shiny Cowbird Molothrus bonariensis is a sexually dichromatic species, in which males have blackish-blue iridescence and females are dull brown. However, in some subtropical parts of its distribution, females show a plumage polymorphism that ranges from dull brown to dark brown and even black. Plumage melanization has been shown to protect feathers from bacterial degradation, decreasing the effects of harmful bacterial activity and thus plumage damage. In this study, we assessed whether bacterial featherdegrading activity is acting as the selective force to increase darkness in the plumage of the female Shiny Cowbirds in Argentina. We compared the degradation of female Shiny Cowbird feathers belonging to different colour morphs when exposed to bacterial strains isolated from subtropical and temperate zones of its distribution, as well as to Bacillus licheniformis. We did not find differences in susceptibility to bacterial degradation between brown feathers and darker feathers. These results suggest that female plumage polymorphism in Shiny Cowbirds has not arisen as a defence against bacterial featherdegrading activity.
Prevalence of feather-degrading Bacillus spp. on the plumage of birds in Australia
Emu - Austral Ornithology, 2019
Bird plumage hosts a diverse microbial community, including microbes capable of degrading the β-keratin in feathers (i.e. feather-degrading bacteria). The prevalence and effects of featherdegrading bacteria have primarily been studied in the Northern Hemisphere, and knowledge of the occurrence of these bacteria on Southern Hemisphere bird species is lacking. We explored the prevalence of feather-degrading bacteria on wild birds in Australia by sampling feathers from 254 individuals representing 25 species. First, to determine the total plumage bacterial load, we sampled bacteria from three body regions and identified and enumerated three presumed featherdegrading Bacillus spp. (B. licheniformis, B. cereus, and B. subtilis) based on morphology. Second, we collected a feather from each bird and in laboratory tests confirmed the presence of featherdegrading bacteria. Third, we tested for a relationship between the number of presumed featherdegrading Bacillus spp. counted and the presence of feather-degrading bacteria on the following variables: habitat type, foraging behaviour, flocking status, and feather wear. We found 85% of birds sampled harboured presumed Bacillus spp. Of the feather samples that tested positive for Bacillus in lab experiments, 62% were confirmed as feather-degrading Bacillus spp. The total plumage bacterial load varied with habitat type, with birds in heath habitats harbouring fewer bacteria. This study is the first report of feather-degrading bacteria on the plumage of wild Australian birds in vivo.