Bacterial composition along the digestive tract of the Horned Screamer (Anhima cornuta), a tropical herbivorous bird

Background

The Horned Screamer (Anhima cornuta) is an herbivorous bird that inhabits wetlands of the South American tropical region. We hypothesize that due to its herbivorous niche, its digestive tract compartments may have bacteria specialized in fermenting complex plant carbohydrates. To test this hypothesis, we compared the bacterial communities along the gastrointestinal tract (GIT) of a Horned Screamer captured in Venezuela.

Methods

Samples were taken from tissues and content of the proventriculus and the small intestine (considered for this study as upper GIT), and the large intestine and cecum (lower GIT). The bacterial community was characterized by sequencing the V4 region of the 16S rRNA gene. Bioinformatic analysis was performed using QIIME, QIITA and Microbiome Analyst. The association between microbial taxonomy and function was analyzed using their Greengenes OTU IDs and a custom KEGG BRITE hierarchical tree and visualized with BURRITO.

Results

The Screamer's gastrointestinal microbiota was composed by seven phyla being Firmicutes and Bacteroidetes the most predominant. The dominant taxa in the upper GIT were Helicobacter, Vibrio, Enterobacter, Acinetobacter and Staphylococcus. The dominant taxa in the lower GIT were Oribacterium, Blautia, Roseburia, Ruminococcus, Desulfovibrio, Intestinimonas, Marvinbryantia and Parabacteroides. Complete degradation of cellulose to the end-products acetate, propanoate, butanoate and acetoacetate was found in the upper and lower GIT without significant differences.

Conclusion

Our study confirmed changes in bacterial community composition throughout the GIT of the Horned Screamer primarily associated with the production of metabolic end-products of carbohydrate digestion essential for the fermentation of the herbivorous diet.

Ventral feathers contained the highest mercury level in brown booby (Sula leucogaster), a pantropical seabird species

Seabirds are extensively used as environmental biomonitors and feathers are among the most analyzed matrices because they are one of the main excretory pathways to detoxify the bird's body of environmental contaminants. Still, there is a variation in contamination level between the different feathers of seabird species, driven by diet and physiology, such as molt strategy and feather formation sequence. We measured total mercury (THg) concentration in different types of feathers (wing, tail, ventral and dorsal) of the same individual in adults and juveniles of brown boobies (Sula leucogaster) from the northern coast of Rio de Janeiro state, Brazil. Brown booby had higher mean THg concentration (μg.g^-1 d. w.) in ventral (adults: 6.46 ± 1.19, 4.79 to 8.34; juveniles: 4.23 ± 0.60, 3.07 to 5.07) and wing (adults: 5.85 ± 1.10, 4.66 to 8.32; juveniles: 3.86 ± 0.54, 3.23 to 4.63), compared to dorsal (adults: 4.52 ± 1.33, 3.01 to 6.44; juveniles: 3.51 ± 0.19, 3.29 to 3.8) and tail feathers (adults: 2.94 ± 0.45, 2.32 to 3.46; juveniles: 2.8 ± 0.23, 2.45 to 3.08). This difference may be explained because feathers grow in a specific sequence during molts leading to different THg concentrations in each type of feather. Additionally, juveniles had significantly lower concentrations of THg than adults in all feather types, which may be explained by the shorter life span, leading to less time to bioaccumulate Hg in their body. It is essential to choose carefully which feather type is more suitable to be used as a biomonitor of THg contamination in a particular species. For brown boobies, we suggest the use of ventral feathers, which represent the highest Hg concentration, are easy to sample and do not impair the seabird's flight ability, although more studies are needed to replicate these results in other tropical seabirds species.

Dawn-song onset coincides with increased HVC androgen receptor expression but is decoupled from high circulating testosterone in an equatorial songbird

The song of songbirds is a testosterone-sensitive behavior that is controlled by brain regions expressing androgen receptors. At higher latitudes, seasonal singing is stimulated by increasing day-length and elevated circulating testosterone. However, a large number of songbird species inhabit equatorial regions under a nearly constant photoperiod, and the neuroendocrine mechanisms of seasonal song in these species have rarely been investigated. We studied males from an equatorial population of the silver-beaked tanager (Ramphocelus carbo), an Amazonian songbird. We found seasonality in dawn-song behavior, which was displayed continuously for more than half a year throughout an extended breeding territoriality stage. The seasonal activation of dawn-song was correlated with an increased area of androgen receptor expression in HVC, a major brain area of song control. However, testosterone levels remained low for several weeks after activation of dawn-song. Circulating levels of testosterone were elevated only later in the breeding season, coinciding with a higher dawn-song output and with the mating period. Our results suggest that the seasonal activation of dawn-song and territoriality involves an increase of androgen target cells in HVC. This mechanism could potentially function to circumvent adverse effects of high testosterone levels in a species with an extended breeding season.