Feather micro-organisms and uropygial antimicrobial defences in a colonial passerine bird

1.  The relationship between the composition of communities of micro-organisms and their hosts remains poorly understood. We conducted extensive field studies of feather-degrading bacteria, other cultivable bacteria, and fungi on the plumage of a migratory bird, the barn swallow Hirundo rustica Linnaeus, to understand the association between micro-organisms, host sociality and host antimicrobial defences, as reflected by the size of the uropygial gland.
2.  The abundance of feather-degrading bacteria, but not other cultivable bacteria or fungi, decreased with increasing size of the uropygial gland.
3.  Females had more feather-degrading bacteria than males.
4.  Barn swallows living in larger colonies had more feather-degrading bacteria than less social conspecifics.
5.  These findings suggest that the uropygial gland plays a specific role in regulating the abundance of feather-degrading bacteria that furthermore depends on the social environment of the host.     

Species richness and abundance of forest birds in relation to radiation at Chernobyl

The effects of low-level radiation on the abundance of animals are poorly known, as are the effects on ecosystems and their functioning. Recent conclusions from the UN Chernobyl forum and reports in the popular media concerning the effects of radiation from Chernobyl on animals have left the impression that the Chernobyl exclusion zone is a thriving ecosystem, filled with an increasing number of rare species. Surprisingly, there are no standardized censuses of common animals in relation to radiation, leaving the question about the ecological effects of radiation unresolved. We conducted standardized point counts of breeding birds at forest sites around Chernobyl differing in level of background radiation by over three orders of magnitude. Species richness, abundance and population density of breeding birds decreased with increasing level of radiation, even after controlling statistically for the effects of potentially confounding factors such as soil type, habitat and height of the vegetation. This effect was differential for birds eating soil invertebrates living in the most contaminated top soil layer. These results imply that the ecological effects of Chernobyl on animals are considerably greater than previously assumed.     

Arrival date and microorganisms in barn swallows

Migration between breeding sites and winter quarters constitute a major life history strategy in birds. The benefits of such migrations must at least equal the costs for such behavior to evolve and be maintained. We tested whether there was a relationship between abundance and diversity of microorganisms on nest lining feathers and timing of arrival by barn swallows Hirundo rustica. Nest lining feathers are chosen and transported by adult barn swallows to their nests just before and during egg laying, at a time when barn swallows have arrived weeks earlier, implying that any heterogeneity in abundance and diversity of microorganisms on feathers in nests must arise from feather preferences. There was a negative relationship between arrival date and the total number of fledglings showing that early arrival is advantageous. The arrival date of adult barn swallows was significantly positively correlated with the abundance of specific bacteria (Bacillus licheniformis) and positively correlated with the abundance of the fungus Trichoderma reesei and negatively correlated with the abundance of the fungus Mucor circinelloides. Moreover, we found a significant positive relationship between arrival date and mean total number of bacterial colonies in TSA medium. There was a significant negative relationship between arrival date and mean total number of bacterial colonies in FMA medium, and Simpson's diversity index of the abundance of bacteria in FMA medium. Such heterogeneity may arise from some microorganisms being beneficial, others detrimental and yet others benign and of no significant importance. In contrast, there was no significant relationship between arrival date and age of individuals. These findings are consistent with the hypothesis that early arriving barn swallows differ in abundance and diversity of microorganisms from late arriving conspecifics, and that they choose feathers for their nests that differ in terms of microorganisms from those chosen by late arrival individuals.     

DNA damage in barn swallows (Hirundo rustica) from the Chernobyl region detected by use of the comet assay

We investigated levels of DNA damage in blood cells of barn swallows (Hirundo rustica) inhabiting the Chernobyl region to evaluate whether chronic exposure to low-level radioactive contamination continues to induce genetic damage in free-living populations of animals. Blood samples were obtained from barn swallows collected at sites with different background levels of radiation, including a relatively uncontaminated area. The extent of DNA damage was evaluated using the alkaline (pH = 12.1) comet assay, a robust and sensitive electrophoresis-based technique widely employed in research ranging from biomonitoring to clinical studies. We found that levels of DNA damage, as indexed by the extent of DNA migration, were increased in barn swallows living in areas surrounding Chernobyl when compared to swallows sampled at low-level sites. The results we obtained are consistent with previous findings on this same species, which showed that swallows breeding in areas heavily contaminated with radionuclides have increased mutation rates, higher oxidative stress and incidence of morphological aberrations and tumors. Overall, these results indicate that chronic exposure to radioactive contaminants, even 20 years after the accident at the Chernobyl nuclear power plant, continues to induce DNA damage in cells of free-living animals.     

Impact of white-rot fungi on numbers and community composition of bacteria colonizing beech wood from forest soil

White-rot fungi are important wood-decomposing organisms in forest ecosystems. Their ability to colonize and decompose woody resources may be strongly influenced by wood-inhabiting bacteria that grow on easily utilizable compounds e.g. oligomers of wood-polymers released by fungal enzymes. However, so far, it is not known how white-rot fungi deal with the presence of potential competing bacteria. Here, the effects of two white-rot fungi, Hypholoma fasciculare and Resinicium bicolor, on the numbers and composition of bacteria colonizing sterile beech wood blocks from forest soil are reported. Both total numbers (microscopic counts) and the numbers of cultivable wood-inhabiting bacteria were considerably lower in wood blocks that became colonized by the white-rot fungi than in control blocks. This points to the fungi out-competing the opportunistic bacteria. The presence of white-rot fungi resulted in a change in the relative abundance of families of cultivable bacteria in wood and also in a change of denaturing gradient gel electrophoresis patterns of directly amplified 16S rRNA gene fragments. Analysis of the bacterial community structure in soil adhering to exploratory mycelium (cords) indicated that fungal species-specific effects on bacterial community composition were also apparent in this fungal growth phase.     

Eggshell Bacterial Load Is Related to Antimicrobial Properties of Feathers Lining Barn Swallow Nests

The use of feathers to line bird’s nests has traditionally been interpreted as having a thermoregulatory function. Feather-degrading bacteria growing on feathers lining nests may have antimicrobial properties, which may provide an additional benefit to lining nests with feathers. We test the hypothesis that the production of antimicrobial substances by feather bacteria affects the microbiological environment of the nest, and therefore the bacterial density on eggshells and, indirectly, hatching success. These effects would be expected to differ between nests lined with pigmented and white feathers, because bacteria grow differently on feathers of different colors. We experimentally manipulated the composition of pigmented and unpigmented feathers in nests of the barn swallow (Hirundo rustica) and studied the antimicrobial properties against the keratin-degrading bacterium Bacillus licheniformis of bacteria isolated from feathers of each color. Analyzed feathers were collected at the end of the incubation period, and antimicrobial activity was defined as the proportion of bacteria from the feathers that produce antibacterial substances effective against B. licheniformis. Our experimental manipulation affected antimicrobial activity, which was higher in nests with only white feathers at the beginning of incubation. Moreover, white feathers showed higher antimicrobial activity than black ones. Interestingly, antimicrobial activity in feathers of one of the colors correlated negatively with bacterial density on feather of the opposite color. Finally, antimicrobial activity of white feathers was negatively related to eggshell bacterial load. These results suggest that antimicrobial properties of feathers in general and of white feathers in particular affect the bacterial environment in nests. This environment in turn affects the bacterial load on eggshells, which may affect hatching success.     

Plumage Bacterial Assemblages in a Breeding Wild Passerine: Relationships with Ecological Factors and Body Condition

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.     

Reduced abundance of insects and spiders linked to radiation at Chernobyl 20 years after the accident

Effects of low-level radiation on abundance of animals are poorly known. We conducted standardized point counts and line transects of bumble-bees, butterflies, grasshoppers, dragonflies and spider webs at forest sites around Chernobyl differing in background radiation by over four orders of magnitude. Abundance of invertebrates decreased with increasing radiation, even after controlling for factors such as soil type, habitat and height of vegetation. These effects were stronger when comparing plots differing in radiation within rather than among sites, implying that the ecological effects of radiation from Chernobyl on animals are greater than previously assumed.     

Reduced abundance of raptors in radioactively contaminated areas near Chernobyl

The negative ecological effects of radioactive contamination around Chernobyl have recently been suggested to be moderate and declining because of an increasing number of anecdotal observations of several species of rare animals including predators. However, these claims were not based on empirical evidence. Radionuclides show bio-accumulation with trophic level, and the abundance of birds is depressed in radioactively contaminated areas around Chernobyl. Therefore, we predicted that birds of prey should be less abundant with increasing levels of radiation. Here, we use our long-term field data from 1991 to 2007 in three different analyses based on observations of raptors using standardized point counts, censuses during capture of barn swallows Hirundo rustica that habitually give alarm calls when a raptor is present, and line transects while driving on roads. Analyses suggest that the abundance of birds of prey is reduced in contaminated areas, and that there is evidence of a recent increase in abundance of raptors in less contaminated areas, but not in the most contaminated ones. Our findings suggest that birds of prey that are top level consumers in ecosystems suffer from reduced abundance in radioactively contaminated areas.     

Historical mutation rates predict susceptibility to radiation in Chernobyl birds

Extreme environmental perturbations are rare, but may have important evolutionary consequences. Responses to current perturbations may provide important information about the ability of living organisms to cope with similar conditions in the evolutionary past. Radioactive contamination from Chernobyl constitutes one such extreme perturbation, with significant but highly variable impact on local population density and mutation rates of different species of animals and plants. We explicitly tested the hypothesis that species with strong impacts of radiation on abundance were those with high rates of historical mutation accumulation as reflected by cytochrome b mitochondrial DNA base‐pair substitution rates during past environmental perturbations. Using a dataset of 32 species of birds, we show higher historical mitochondrial substitution rates in species with the strongest negative impact of local levels of radiation on local population density. These effects were robust to different estimates of impact of radiation on abundance, weighting of estimates of abundance by sample size, statistical control for similarity in the response among species because of common phylogenetic descent, and effects of population size and longevity. Therefore, species that respond strongly to the impact of radiation from Chernobyl are also the species that in the past have been most susceptible to factors that have caused high substitution rates in mitochondrial DNA.     

Selection and characterization of feather-degrading bacteria from canola meal compost

Canola meal that contains a high level of protein (40% crude protein) was used as compost material for the isolation of feather-degrading bacteria. After 7 and 14 days, bacteria were isolated from compost amended and unamended with soil. Eighty bacterial isolates from canola meal compost were then grown on milk-agar and isolates that produced proteolytic enzymes were identified by the formation of clear haloes around the colonies. A feather medium was chosen for a secondary selection of feather-degrading isolates. Of the eight isolates that hydrolyzed milk protein, five isolates hydrolyzed feathers. Their keratinolytic activities were subsequently confirmed by an assay using azo-keratin as substrate. Seven of the eight bacteria that hydrolyzed milk protein were Bacillus spp, and all five isolates that hydrolyzed feathers were strains of Bacillus licheniformis. Protease inhibition studies indicated that serine proteases are the predominant proteolytic enzymes produced by these feather-degrading isolates. Received 02 April 1999/ Accepted in revised form 17 June 1999     

Inter‐annual and body topographic consistency in the plumage bacterial load of Great Tits

ABSTRACT Plumage bacteria may play an important role in shaping the life histories of birds. However, to design suitable experiments to examine causal relationships between plumage bacteria and the fitness of host birds, natural variation in plumage bacterial communities needs to be better understood. We examined within‐individual consistency of plumage bacterial contamination in Great Tits (Parus major), comparing different body regions (ventral vs. dorsal) and comparing contamination between years. Numbers of free‐living and attached bacteria and the species richness of feather‐degrading bacterial assemblages were studied using flow cytometry and ribosomal intergenic spacer analysis (RISA). Numbers of both types of bacteria were higher on dorsal than on ventral feathers. Numbers of free‐living, but not attached, bacteria on the two body regions were highly positively correlated. There was also a strong within‐individual correlation between numbers of attached bacteria during the same breeding stages in different years. These results suggest that, despite variation in absolute levels of feather bacterial loads between years and different body regions, sampling individual birds can provide reliable estimates of relative levels of bacterial contamination, as long as sampling time and body region are carefully standardized.     

ALBINISM AND PHENOTYPE OF BARN SWALLOWS (HIRUNDO RUSTICA) FROM CHERNOBYL

Abstract The effects of mutation on phenotypic expression are supposed to be mainly deleterious because mutations disrupt the expression of genes that function relatively well under current environmental conditions. Thus, mutations are assumed to give rise to deviant phenotypes that are generally selected against. Radioactive contamination in the Chernobyl region of Ukraine is associated with a significant increase by a factor two to 10 in mutation rate in microsatellite markers of the barn swallow, Hirundo rustica. Barn swallows from Chernobyl had a temporally constant, elevated frequency of partial albinism compared to the situation before radioactive contamination and compared to birds from a control area. Albinism disproportionately affected the carotenoid‐based plumage of the head, suggesting that carotenoid metabolism is particularly susceptible to the effects of radiation. Individuals with partially albinistic plumage had, on average, lower mean phenotypic values than other birds, and this was particularly the case for males. Furthermore, differences in phenotypic variation, as determined using Levene's test, were significantly larger in partial albinos compared to nonalbinos in males, but not in females, even though the null expectation would be the opposite due to the lower mean phenotypic values of partial albinos. Although small phenotypes were commonly associated with germline mutations, there was no general decrease in overall body size during the period 1991–2000, implying that small individuals were selected against. Because partial albinism is disfavored by natural selection, the effects of mutations are deleterious, giving rise to a balance between mutation and selection.     

Brood size modifications affect plumage bacterial assemblages of European starlings

During reproduction, birds face trade-offs between time and energy devoted to parental effort and traits associated with self-maintenance. We manipulated brood sizes to investigate the effects of such trade-offs on feather bacterial densities and the structure of bacterial assemblages on feathers in adult European starlings, Sturnus vulgaris, and in vitro feather degradation. As predicted by a trade-off between parental effort and self-maintenance, we found that birds with enlarged broods had more free-living bacteria on their feathers than birds with reduced broods. Furthermore, we found a significant interaction between brood manipulation and original brood size on free-living bacterial densities suggesting that the trade-off is mediated by the adults' initial reproductive investment. In contrast, brood size manipulations had no significant effect on densities of attached bacteria. Using ribosomal intergenic spacer analysis (RISA), we demonstrated that brood manipulations significantly modified the structure (band pattern) of feather-degrading bacterial assemblages, but had no significant effect on their richness (number of bands) or the in vitro feather degradation. In vitro feather degradation varied in relation to the premanipulation brood size and positively with the richness of the feather degrading bacterial community. Besides brood manipulation effect, we found that ecological factors and individual traits, such as the age, the nest location or the capture date, shaped bacterial assemblages and feather degradation capacities.     

Carotenoids, sexual signals and immune function in barn swallows from Chernobyl.

Carotenoids have been hypothesized to facilitate immune function and act as free-radical scavengers, thereby minimizing the frequency of mutations. Populations of animals exposed to higher levels of free radicals are thus expected to demonstrate reduced sexual coloration if use of carotenoids for free-radical scavenging is traded against use for sexual signals. The intensity of carotenoid-based sexual coloration was compared among three populations of barn swallows Hirundo rustica differing in exposure to radioactive contamination. Lymphocyte and immunoglobulin concentrations were depressed, whereas the heterophil:lymphocyte ratio, an index of stress, was enhanced in Chernobyl swallows compared to controls. Spleen size was reduced in Chernobyl compared to that of two control populations. Sexual coloration varied significantly among populations, with the size of a secondary sexual character (the length of the outermost tail feathers) being positively related to coloration in the two control populations, but not in the Chernobyl population. Thus the positive covariation between coloration and sexual signalling disappeared in the population subject to intense radioactive contamination. These findings suggest that the reliable signalling function of secondary sexual characters breaks down under extreme environmental conditions, no longer providing reliable information about the health status of males.     

Antioxidants, radiation and mutation as revealed by sperm abnormality in barn swallows from Chernobyl

Reduced levels of antioxidants such as carotenoids and vitamins A and E can increase DNA damage caused by free radicals. Exposure to radiation has been proposed to reduce levels of antioxidants that are used for DNA repair and this reduction may be responsible for increased levels of mutation in radioactively contaminated areas. We test this hypothesis using field measures of antioxidants in blood, liver and eggs of the barn swallow Hirundo rustica while relating these to levels of mutation as reflected by the frequency of abnormal sperm. Antioxidant levels in blood, liver and eggs were reduced in Chernobyl, Ukraine, compared with an uncontaminated control area, and levels of antioxidants correlated negatively with levels of background radiation. The frequency of abnormal sperm was almost an order of magnitude higher in Chernobyl than in the control area and was negatively related to antioxidant levels in blood and liver. This is consistent with the hypothesis of a direct link between radiation and individual levels of antioxidants, suggesting that levels of mutation differ among individuals owing to individual differences in the abundance of antioxidants.     

Cohabitation with farm animals rather than breeding effort increases the infection with feather‐associated bacteria in the barn swallow Hirundo rustica

Feather‐associated bacteria are widespread inhabitants of avian plumage. However, the determinants of the between‐individual variation in plumage bacterial loads are less well understood. Infection intensities can be determined by ecological factors, such as breeding habitat, and can be actively regulated by hosts via preening. Preening, yet, is a resource intensive activity, and thus might be traded‐off against reproductive investment in breeding birds. Here, we studied barn swallows Hirundo rustica to assess the bacterial cost of reproduction in relation to nesting site micro‐habitats. Barn swallows prefer to breed in the company of large‐sized farm animals, although the presence of mammalian livestock in barns assures a warm and humid micro‐climate that favours bacterial proliferation. Thus, we experimentally manipulated brood sizes of birds breeding in barns with, or without, farm animals and measured total cultivable bacteria (TCB) and feather‐degrading bacteria (FDB) from the plumage. We found that the abundance of feather‐associated bacteria (i.e. both TCB and FDB) in females, but not males, breeding in barns with livestock were significantly higher than in conspecifics breeding in empty barns. Plumage bacterial loads, however, were not affected by brood size manipulations in either sex. In addition, we report a negative relationship between both TCB and FDB and hatching date in females, and several sex and seasonal differences in plumage bacterial abundances. Our study is the first to show that breeding micro‐habitat (i.e. livestock co‐tenancy) has consequences for the abundance of feather‐associated bacteria.     

Increased oxidative stress in barn swallows from the Chernobyl region

The Chernobyl nuclear accident produced the largest unintended release of radionuclides in history, with dramatic consequences for humans and other organisms. Exposure to ionizing radiation is known to reduce circulating and stored levels of specific antioxidants in birds and humans, thus potentially increasing oxidative stress. However, overall effects of radioactive exposure on oxidative status have never been investigated in any free ranging vertebrate. We measured plasma antioxidant capacity and concentration of reactive oxygen metabolites in adult barn swallows (Hirundo rustica) from colonies with variable background radiation levels in the Chernobyl region in Ukraine and Belarus. We predicted that antioxidants would decrease while reactive oxygen metabolites would increase with exposure to increasing levels of radiation at the breeding sites. Consistent with this expectation, radiation level positively predicted plasma concentration of reactive oxygen metabolites, whereas no significant covariation was found with non-enzymatic plasma antioxidant capacity. An index of oxidative stress was also larger in barn swallows exposed to high contamination levels. Thus, radioactive contamination appeared to be responsible for the increased generation of reactive oxygen metabolites and the imbalance between reactive oxygen metabolites and non-enzymatic plasma antioxidant capacity.     

Symbiotic feather mites synchronize dispersal and population growth with host sociality and migratory disposition

Some symbiotic taxa may have evolved to track changes in the level and quality of food resources provided by the host to increase reproduction and dispersal. As a consequence, some ectosymbionts synchronize their reproduction and activity with particular stages of their host's living cycle. In this article we examined temporal patterns of variation in prevalence and abundance of feather mites living on pre‐migratory barn swallows Hirundo rustica. Feather mites in the lineages Pterolichoidea and Analgoidea are the most common arthropod ectosymbionts living at the expenses of feather oil. We investigated whether the seasonal variations in levels of several measures of physiological condition associated with host migration were related to changes in prevalence and abundance of mites. The results suggest that the variation in prevalence of feather mites, and thus probably the mode of acquisition and dispersal of these symbionts, is linked to an increase in host sociality before migration. Physiological dynamics of hosts after the breeding season point at two clearly identifiable periods: a post‐breeding period when physiological condition remains stationary or decreases, and a pre‐migratory period characterized by a rapid increase in several measures of physiological condition. Mite population dynamics were synchronized with migratory disposition during the period of highest host gregariousness. These synchronized processes occurred in both study years, although dynamics of migratory disposition and mite prevalence and abundance differ somewhat between years for adult and juvenile hosts. Mite population increase before host migration may be a response to a higher quantity of food provided by the host, namely oil from the urpoygial gland which is stimulated by hormones. Therefore, mites might have evolved to adjust their reproduction to the time when they have more chance of dispersal through horizontal transmission. In addition, body mass of juvenile and adult hosts were positively related with mite abundance in both years after allowing for several influencing factors. Body mass variation may reflect adequately fitness of host or their current physiological state, for instance, differences in the secretion of lipids on feathers or a more adequate microclimate to these symbionts.