A groundbreaking study that could have important implications for promoting healthier ecosystems and wildlife populations.
The microbiome has been getting a fair bit of press attention recently because there is more and more evidence to suggest that it influences development, health and fitness. The microbiome is the community of microorganisms, including bacteria, viruses, fungi, archaea and other microbes, that live on or inside the body. The microbiome interacts with the environment and acts as a kind of bridge between the environment and the body that affects overall health in many ways.
Wild bird health is linked to their microbiome
When you hear or read the word “microbiome”, you probably think of the microbial community that inhabits the gut. Whilst links between the gut microbiome and other traits have been described in laboratory experiments with captive or domesticated animals (read more here and here), little is known about these relationships in wild animals — and surprisingly, even less is known in wild birds (but see this — and even this is an eye-opening study).
To better understand the connection between the gut microbiome and physical traits as well as overall health in birds, a team of scientists spent five years examining this relationship.
“After a preliminary project with captive zebra finches, I wanted to work with wild populations for a more natural, transferrable test of these relationships,” said the study’s lead author, avian ecologist Morgan Slevin, who is studying Integrative Biology and Neuroscience at Florida Atlantic University. This study is part of Dr Slevin’s dissertation, which he defended last week to meet part of the requirements for the PhD.
To build on his zebra finch study and to expand it to a wild bird species, Dr Slevin chose the Northern cardinal, Cardinalis cardinalis, as his study organism. Cardinals are common garden birds in the eastern part of the United States. Adult males are known for their ornaments — brilliant scarlet plumage and beak that contrast sharply with a coal black mask.
“Cardinals are a very tractable system because they’re common, easy to catch, and coloration and the stress response have already been well described … all that was left was to study their gut microbiome,” Dr Slevin explained to me in email.
To test for relationships between microbiota and host fitness, Dr Slevin and collaborators sampled the cloacal microbiomes of wild cardinals and measured body condition index, assessed coloration of sexual ornaments (beak and plumage), and collected blood to estimate the glucocorticoid response to stress (Figure 1).
The Northern cardinal’s sexually selected coloring are a well-known example of how carotenoid pigments are an honest signal of an individual’s quality, and this provided Dr Slevin and collaborators a unique opportunity to explore how these traits are linked to gut microbiota.
“Overall, cardinal ornament redness and saturation positively correlate with individual quality,” Dr Slevin said in email. “Thus, deeper red coloration indicates greater carotenoid pigmentation. We were able to show that a cardinal’s coloration related to its microbiome diversity.”
Microbiome diversity is known to affect host fitness: low diversity can lead to immune issues and poor nutrient absorption, whilst high diversity can boost resilience to stress and pathogens. But microbiome diversity may also affect other traits — traits that relate to health and breeding success.
“We took a particular interest in carotenoid-pigmented ornaments because, in additional to this signal honesty, they act as antioxidants and play a role in the immune system,” Dr Slevin continued. “Cardinals also have melanin-pigmented masks, which we found predicted alpha and beta diversity, so clearly this ornament-microbiome relationship is not limited to carotenoids.”
Alpha diversity is a measure of the richness and evenness of a sample’s microbiome. For example, a sample with high alpha diversity has many species that are equally abundant. Beta diversity measures the variability in the composition of a microbiome between samples. Thus, in this system, high beta diversity indicates that samples share few species, whilst low beta diversity reveals that the samples share most of their species.
The study found several important connections: Both alpha and beta bacterial diversity were related to individual variation in body condition and plumage color saturation, but glucocorticoid (a stress hormone) concentrations were not. Additionally, beak color saturation was related to beta diversity, suggesting birds with similar beak coloration profiles had more similar microbiome community structures.
“While we anticipated that birds with the most saturated beaks would be the highest quality individuals, and that the highest quality individuals would have the most diverse microbiomes, our results suggest that maintaining a diverse microbiome might instead come at a cost to beak saturation,” Dr Slevin explained.
What was the most interesting finding of this study?
“The most interesting thing was the sheer number of ornaments (we measured 5) that showed at least one relationship with microbiome diversity,” Dr Slevin replied in email.
“I liked the logic behind our hypothesis that carotenoid ornaments would relate to microbiome characteristics,” Dr Slevin added in email, “but honestly I thought it would be a little too good to be true, or at least not a strong enough signal to shine through the noise of a free-living study system.”
“It was a pleasant surprise to have our hypothesis supported,” Dr Slevin concluded.
“Our findings confirm the hypothesis that a wild bird’s health is tied to its microbiome, and that the ‘sexiness’ of a male’s ornaments can signal his health,” agreed the study’s senior author, animal ethologist Rindy Anderson, an associate professor in FAU’s Department of Biological Sciences where she specializes in studying social behavior, communication, and cognition.
“Ultimately, our study and those that follow should move us closer to answering the overall question of whether a bird’s gut microbiome can predict individual quality,” Professor Anderson noted.
Although these findings are a nice addition to the small but growing body of research that links physical traits and overall health of individual wild birds to their microbiome, are there any practical applications for this work?
“This study has important applications for conservation biology and contributes to a better understanding of ways to improve animal health in settings such as wildlife hospitals, zoos and aquaria, and captive breeding programs for endangered species,” Dr Slevin responded.
By continuing to explore these connections, scientists seek to better understand how microbiomes influence the health and survival of living organisms. In the end, understanding these microbial relationships may hold the key to promoting healthier ecosystems and wildlife populations.
Source:
Morgan C. Slevin, Jennifer L. Houtz, Maren N. Vitousek, Daniel T. Baldassarre, and Rindy C. Anderson (2024). Ornamentation and body condition, but not glucocorticoids, predict wild songbird cloacal microbiome community and diversity, Oikos e10905 | doi:10.1111/oik.10905
© Copyright by GrrlScientist | hosted by Forbes | LinkTr.ee
Socials: Bluesky | CounterSocial | Gab | LinkedIn | Mastodon Science | Spoutible | SubStack | Threads | Tribel | Tumblr | Twitter
