Brood size modifications affect plumage bacterial assemblages of European starlings

The microbiome of African penguins (Spheniscus demersus) under managed care resembles that of wild marine mammals and birds

Animals under managed care in zoos and aquariums are ideal surrogate study subjects for endangered species that are difficult to obtain in the wild. We compared the fecal and oral microbiomes of healthy, managed African penguins (Spheniscus demersus) to those of other domestic and wild vertebrate hosts to determine how host identity, diet, and environment shape the penguin microbiome. The African penguin oral microbiome was more similar to that of piscivorous marine mammals, suggesting that diet and a marine environment together play a strong role in shaping the oral microbiome. Conversely, the penguin cloaca/fecal microbiome was more similar to that of other birds, suggesting that host phylogeny plays a significant role in shaping the gut microbiome. Although the penguins were born under managed care, they had a gut microbiome more similar to that of wild bird species compared to domesticated (factory-farmed) birds, suggesting that the managed care environment and diet resemble those experienced by wild birds. Finally, the microbiome composition at external body sites was broadly similar to that of the habitat, suggesting sharing of microbes between animals and their environment. Future studies should link these results to microbial functional capacity and host health, which will help inform conservation efforts.

Ecological Processes and Human Behavior Provide a Framework for Studying the Skin Microbial Metacommunity

Metacommunity theory dictates that a microbial community is supported both by local ecological processes and the dispersal of microbes between neighboring communities. Studies that apply this perspective to human-associated microbial communities are thus far limited to the gut microbiome. Yet, the skin serves as the primary barrier between the body and the external environment, suggesting frequent opportunities for microbial dispersal to the variable microbial communities that are housed across skin sites. This paper applies metacommunity theory to understand the dispersal of microbes to the skin from the physical and social environment, as well as between different skin sites on an individual's body. This includes highlighting the role of human behavior in driving microbial dispersal, as well as shaping physiological properties of skin that underscore local microbial community dynamics. By leveraging data from research on the skin microbiomes of amphibians and other animals, this paper provides recommendations for future research on the skin microbial metacommunity, including generating testable predictions about the ecological underpinnings of the skin microbiome.

Increased allocation to reproduction reduces future competitive ability in a burying beetle

The existence of a trade-off between current and future reproduction is a fundamental prediction of life history theory. Support for this prediction comes from brood size manipulations, showing that caring for enlarged broods often reduces the parent's future survival or fecundity. However, in many species, individuals must invest in competing for the resources required for future reproduction. Thus, a neglected aspect of this trade-off is that increased allocation to current reproduction may reduce an individual's future competitive ability. We tested this prediction in the burying beetle, Nicrophorus vespilloides, a species where parents care for their offspring and where there is fierce competition for resources used for breeding. We manipulated reproductive effort by providing females with either a small brood of 10 larvae or a large brood of 40 larvae and compared the ability of these females, and virgin females that had no prior access to a carcass, to compete for a second carcass against a virgin competitor. We found that increased allocation to current reproduction reduced future competitive ability, as females that had cared for a small brood were more successful when competing for a second carcass against a virgin competitor than females that had cared for a large brood. In addition, the costs of reproduction were offset by the benefits of feeding from the carcass during an initial breeding attempt, as females that had cared for a small brood were better competitors than virgin females that had no prior access to a carcass, whilst females that had cared for a large brood were similar in competitive ability to virgin females. Our results add to our understanding of the trade-off between current and future reproduction by showing that this trade-off can manifest through differences in future competitive ability and that direct benefits of reproduction can offset some of these costs.

The skin microbiome of vertebrates

The skin constitutes the primary physical barrier between vertebrates and their external environment. Characterization of skin microorganisms is essential for understanding how a host evolves in association with its microbial symbionts, modeling immune system development, diagnosing illnesses, and exploring the origins of potential zoonoses that affect humans. Although many studies have characterized the human microbiome with culture-independent techniques, far less is known about the skin microbiome of other mammals, amphibians, birds, fish, and reptiles. The aim of this review is to summarize studies that have leveraged high-throughput sequencing to better understand the skin microorganisms that associate with members of classes within the subphylum Vertebrata. Specifically, links will be explored between the skin microbiome and vertebrate characteristics, including geographic location, biological sex, animal interactions, diet, captivity, maternal transfer, and disease. Recent literature on parallel patterns between host evolutionary history and their skin microbial communities, or phylosymbiosis, will also be analyzed. These factors must be considered when designing future microbiome studies to ensure that the conclusions drawn from basic research translate into useful applications, such as probiotics and successful conservation strategies for endangered and threatened animals.

Manipulation of parental effort affects plumage bacterial load in a wild passerine

It has been suggested that plumage microorganisms play an important role in shaping the life histories of wild birds. Some bacteria may act as pathogens or cause damage to feathers, and thereby reduce individual fitness. Intense parental care in birds can result in a reduction of self-maintenance and preening behavior in parents and therefore might affect the dynamics of microbiota living on their feathers. However, experimental evidence of this relationship is virtually absent. We manipulated the parental effort of wild breeding pied flycatcher (Ficedula hypoleuca) females by modifying their brood size or temporarily removing male partners. We expected that experimentally decreasing or increasing parental effort would affect feather sanitation in females and therefore also bacterial density on their plumage. In accordance with this hypothesis, manipulation affected the density of free-living bacteria: females with reduced broods had the lowest number of free-living bacteria on their feathers, while females left without male partners had the highest. However, manipulation did not have a significant effect on the densities of attached bacteria. Our results provide experimental evidence that a trade-off between self-maintenance and parental effort affects plumage bacterial densities in birds.

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

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.

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

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.

Conclusion

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.

Effect of preen oil on plumage bacteria: an experimental test with the mallard

Feathers are essential for avian thermoregulation, communication or flight and a reduction of plumage condition may alter these functions and reduce individual fitness. Recently, descriptive studies provided evidence that birds carry feather-degrading bacteria on their plumage that have the ability to degrade feathers rapidly under laboratory conditions. If such bacteria reduce avian fitness, natural selection should favour the evolution of anti-bacterial defences to limit the effects of these detrimental microorganisms. Preening behaviour and associated preen gland secretions have been proposed as the main factor used by birds to limit feather-degrading bacterial growth and some recent in vitro studies provided evidence that uropygial oil inhibited the growth of some keratinolytic strains in passerines. However, preen oil antimicrobial properties remained to be experimentally tested in vivo. We conducted an experiment with mallards (Anas platyrhynchos) onto which we fixed a removable mechanism that blocked access to the uropygial gland in a first group of mallards, whilst birds in a second group had the same removable mechanism but access to their gland and a third group of birds had normal access to their gland. We found no significant effect of our treatment on total and feather-degrading bacterial loads. Three hypotheses may explain the discrepancy between our results and previous in vitro studies. First, in vitro studies may have over-estimated the bactericidal properties of the preen oil. Second, preen gland deprivation may have affected only a small portion of the feather-degrading bacterial community. Third, ducks and passerine oils might have different bactericidal properties.

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.

Microorganisms associated with feathers of barn swallows in radioactively contaminated areas around chernobyl

The Chernobyl catastrophe provides a rare opportunity to study the ecological and evolutionary consequences of low-level, environmental radiation on living organisms. Despite some recent studies about negative effects of environmental radiation on macroorganisms, there is little knowledge about the effect of radioactive contamination on diversity and abundance of microorganisms. We examined abundance patterns of total cultivable bacteria and fungi and the abundance of feather-degrading bacterial subset present on feathers of barn swallows (Hirundo rustica), a colonial migratory passerine, around Chernobyl in relation to levels of ground level environmental radiation. After controlling for confounding variables, total cultivable bacterial loads were negatively correlated with environmental radioactivity, whereas abundance of fungi and feather-degrading bacteria was not significantly related to contamination levels. Abundance of both total and feather-degrading bacteria increased with barn swallow colony size, showing a potential cost of sociality. Males had lower abundance of feather-degrading bacteria than females. Our results show the detrimental effects of low-level environmental radiation on total cultivable bacterial assemblage on feathers, while the abundance of other microorganism groups living on barn swallow feathers, such as feather-degrading bacteria, are shaped by other factors like host sociality or host sex. These data lead us to conclude that the ecological effects of Chernobyl may be more general than previously assumed and may have long-term implications for host-microbe interactions and overall ecosystem functioning.

Symbiotic bacteria living in the hoopoe's uropygial gland prevent feather degradation

Among potential agents that might damage bird feathers are certain microorganisms which secrete enzymes that digest keratin, as is the case of the ubiquitous bacterium Bacillus licheniformis, present in both the feathers and skin of wild birds. It is therefore a good candidate for testing the effects of bird defences against feather-degrading microorganisms. One of these defences is the oil secreted by the uropygial gland, which birds use to protect their feathers against parasites. In previous studies we have shown how Enterococcus faecalis strains isolated from nestling hoopoes exert antagonistic effects against B. licheniformis, mediated by the production of bacteriocins. Consequently we hypothesized that this enterococcus and the bacteriocins it engenders might act as a defence against feather-degrading microorganisms in hoopoes. We investigated this hypothesis in a series of laboratory experiments and evaluated the extent to which the keratinolytic effects caused by B. licheniformis were reduced by the E. faecalis MRR10-3 strain, isolated from hoopoes, and its bacteriocins. In different treatments, feathers or pure keratin was incubated with B. licheniformis, B. licheniformis together with E. faecalis MRR10-3, and B. licheniformis together with the bacteriocins produced by E. faecalis MRR10-3. Our results were in accordance with the predicted effects on hoopoe feathers. There was a significant decrease both in pure keratin loss and in feather degradation in the presence of the symbiotic bacterium or its bacteriocin. These results suggest that by preening their feathers hoopoes benefit from their symbiotic relationship with bacteriocin-producing enterococci, which constitute a chemical defence against feather degradation.

Variation in plumage microbiota depends on season and migration

Migratory birds can be efficient dispersers of pathogens, yet we know little about the effect of migration and season on the microbial community in avian plumage. This is the first study to describe and compare the microbial plumage community of adult and juvenile migratory birds during the annual cycle and compare the plumage community of migrants to that of resident birds at both neotropical and nearctic locations. We used length heterogeneity PCR (16S rRNA) to describe the microbial assemblage sampled from the plumage of 66 birds in two age classes and from 16 soil samples. Resident birds differed significantly in plumage microbial community composition from migrants (R > or = 0.238, P < 0.01). Nearctic resident birds had higher plumage microbial diversity than nearctic migrants (R = 0.402, P < 0.01). Plumage microbial composition differed significantly between fall premigratory and either breeding (R > or = 0.161, P < 0.05) or nonbreeding stages (R = 0.267, P < 0.01). Six bacterial operational taxonomic units contributed most to the dissimilarities found in this assay. Soil microbial community composition was significantly different from all samples of plumage microbial communities (R > or = 0.700, P < 0.01). The plumage microbial community varies in relation to migration strategy and stage of the annual cycle. We suggest that plumage microbial acquisition begins in the first year at natal breeding locations and reaches equilibrium at the neotropical wintering sites. These data lead us to conclude that migration and season play an important role in the dynamics of the microbial community in avian plumage and may reflect patterns of pathogen dispersal by birds.

Bacteria as an agent for change in structural plumage color: correlational and experimental evidence

Recent studies have documented that a diverse assemblage of bacteria is present on the feathers of wild birds and that uropygial oil affects these bacteria in diverse ways. These findings suggest that birds may regulate the microbial flora on their feathers. Birds may directly inhibit the growth of harmful microbes or promote the growth of other harmless microbes that competitively exclude them. If keratinolytic (i.e., feather-degrading) bacteria degrade colored feathers, then plumage coloration could reveal the ability of individual birds to regulate microbial flora. We used field- and lab-based methods to test whether male eastern bluebirds (Sialia sialis) with brighter blue structural plumage coloration were better able to regulate their microbial flora than duller males. When we sampled bluebirds in the field, individuals with brighter color had higher bacterial loads than duller individuals. In the lab, we tested whether bacteria could directly alter feather color. We found that keratinolytic bacteria increased the brightness and purity, decreased the ultraviolet chroma, and did not affect the hue of structural color. This change in spectral properties of feathers may occur through degradation of the cortex and spongy layer of structurally colored barbs. These data suggest that bacteria can alter structural plumage color through degradation.

A molecular comparison of plumage and soil bacteria across biogeographic, ecological, and taxonomic scales

We used molecular methods to determine the microbial community of soil and avian plumage across biogeographic, ecological, and taxonomic scales. A total of 17 soil and 116 feather samples were collected from five avian species across multiple habitat types within one Neotropical and one temperate locality. Hypotheses regarding patterns of microbial composition relative to acquisition and dispersal of plumage bacteria in the ecosystem were tested by comparing microbial communities within and between soil and plumage. Samples from the plumage of American Redstarts (Setophaga ruticilla) were collected across both habitat types and geographic scales for intraspecific comparisons. The microbial diversity in avian plumage was moderately diverse and was dominated by Pseudomonas species. Despite a highly significant individual bird effect on microbial composition of the plumage, we detected significant biogeographic and type of habitat effects. Pseudomonas species were more abundant on the temperate site when all avian species were included in the analysis, and Bacillus subtilis and Xanthomonas groups were more abundant on the Neotropical site for redstarts alone. However, 16S rDNA sequence libraries were not significantly different between Jamaican and Maryland redstarts. Biogeographic and habitat effects were significant and more pronounced for soil samples indicating lower dispersal of soil microbiota. We detected a significant difference between soil and plumage microbial communities suggesting that soil plays a small role in plumage bacterial acquisition. Our results suggest bacterial communities on the plumage of birds are dynamic and may change at different stages in a bird's annual cycle.

Social and sexual behaviours aid transmission of bacteria in birds

Understanding the behavioural mechanisms that mediate pathogen transmission in social hosts like birds could provide the empirical bases for explaining the epidemiological dynamics of zoonotic infections in vertebrates. By experimentally infecting the feathers and cloaca of captive zebra finches (Taeniopygia guttata), with the bacterium Bacillus licheniformis PWD1 (BL), we examined the self-contamination and horizontal transmission of birds sharing the same environment. We also examined whether sexual transmission of bacteria is gender biased. Our results show that bacteria placed on the plumage of the birds lead to self and allo-infections of the bird guts, possibly through preening behaviours and bacterial ingestion. Furthermore, we found that sexual transmission of the bacteria was asymmetrical, being higher when males are the transmitting sex. Our results suggest the existence of an oral-faecal-genital route of bacterial transmission for avian hosts, wherein bacteria present on feathers infect their host guts through self and allo-preening and bacterial ingestion. Gut bacteria can then be transmitted sexually with transmission rate being higher when males are the infected sex.

Host–symbiont relationship and abundance of feather mites in relation to age and body condition of the barn swallow (Hirundo rustica): an experimental study

We analyzed the host–symbiont relationship and factors determining the abundance of feather mites among individual barn swallows (Hirundo rustica L., 1758) in two different host populations during the breeding season and postbreeding period. By experimentally removing the feather mites from the flight feathers of the birds with an insecticide, we showed that these symbiotic organisms have neither harmful nor beneficial effects on the fitness of the host, supporting the view that mites are commensals. This was indicated by the lack of any difference in the change in wing-feather length, tail-feather length, fluctuating asymmetry in tail-feather length, breeding performance, and survival of the birds between the fumigated and control groups 1 year after the experiment. During the postbreeding period juveniles harbored fewer mites than adults and the difference was also significant between the 1-year-old birds and those over 1 year old in the breeding population. The number of mites did not change after the second year of life of the birds. We hypothesize that the difference in abundance of mites between the age classes can be explained by the low reproductive potential of the mites, which are not able to populate the exploitable space until the second year of life of the host. Alternatively, young birds might provide fewer resources than old birds. The significant negative association between the number of mites and the laying date of female barn swallows seems to support the conclusion that the abundance of mites is condition-dependent. Because there was no relationship between other condition indices for males and females and number of mites, further research is needed to confirm this conclusion.