The Wild World Within
How Bank Voles Are Revolutionizing Our Understanding of Gut Ecosystems
Exploring the complex interactions in bank vole gut microbiomes and their implications for health and environment
The Secret World Within—Why Bank Voles Are Microbial Supermodels
Deep within the forests of Europe, a tiny, unassuming rodent holds secrets that are transforming our understanding of complex ecosystems—not in the forests it inhabits, but in its own gut.
The bank vole (Myodes glareolus), with its reddish-brown fur and small, mouse-like appearance, has become an unexpected superstar in the world of microbiome research. These common creatures are helping scientists unravel the intricate relationships between animals and the trillions of microorganisms that call their digestive systems home.
Bank voles in their natural habitat provide unique insights into microbiome dynamics.
Why study bank voles? Unlike laboratory mice that live in carefully controlled environments, bank voles experience the full complexity of the natural world—changing seasons, diverse diets, environmental pollutants, and a constant array of pathogens. This makes their gut microbiomes incredibly dynamic and rich with information about how environmental factors shape these internal ecosystems 3 .
Did You Know?
Bank voles have one of the most diverse gut microbiomes among small mammals, making them ideal for studying microbial interactions.
Recent research on these unassuming rodents has revealed that the interactions within their gut microbiomes are far more complex than anyone previously imagined, with implications that extend to human health, wildlife conservation, and our understanding of how animals adapt to changing environments.
What Makes a Microbiome—The Players and Their Roles
The Microbial Universe Inside a Gut
The gut microbiome refers to the vast collection of microorganisms—bacteria, fungi, viruses, and other microbes—that inhabit the digestive tracts of animals. In bank voles, as in humans, these microbial communities are dominated by two main bacterial phyla: Bacteroidetes (35-75%) and Firmicutes (20-47%), with smaller contributions from Proteobacteria (2-9%) and Spirochaetes (3-12%) 5 .
These percentages aren't just abstract numbers—they represent a complex ecosystem where different microbial species perform specialized functions, from breaking down otherwise indigestible plant materials to producing essential vitamins and training the immune system.
Typical bacterial composition in bank vole gut microbiomes 5
The Flexibility vs. Resistance Debate
Scientists studying microbiomes often debate two competing concepts: flexibility (how quickly microbes can change in response to new environments or diets) versus resistance (how much they remain stable despite external changes) 1 .
This tension between change and stability is at the heart of understanding how animals adapt to environmental challenges. Bank vole research has revealed that their gut microbiomes exhibit both characteristics depending on life stage and environmental factors, creating a dynamic balance that contributes to the voles' remarkable adaptability across diverse habitats.
Bacteroidetes (B), Firmicutes (F), Proteobacteria (P), and Spirochaetes (S) interact dynamically in the vole gut
The Reciprocal Transplant—A Microbial Journey Between Habitats
Experimental Design: From Urban to Rural and Back Again
To understand how environment shapes the gut microbiome, researchers designed an elegant reciprocal transfer experiment 1 . They captured wild bank voles from both urban and rural forests in Finland, then performed a carefully orchestrated swap: some urban voles were relocated to rural forests, while some rural voles were moved to urban habitats.
The team monitored both adult voles and their offspring, tracking how their gut microbiomes changed in response to their new environments.
Experimental Process
Initial Capture
Gravid bank voles from 20 urban and 20 rural forest sites
Laboratory Monitoring
Until voles gave birth (3-20 days)
Transfer
Voles with offspring to new forest patches
Recapture
After 3-4 weeks to sample gut microbiota
Sample Collection Data
| Group | Transfer Direction | Number of Adults | Number of Offspring |
|---|---|---|---|
| 1 | Rural → Rural | 7 | 17 |
| 2 | Rural → Urban | 5 | 26 |
| 3 | Urban → Rural | 7 | 10 |
| 4 | Urban → Urban | 9 | 19 |
Sample collection in the reciprocal transfer experiment 1
Resilience and Change—How Vole Microbiomes Respond to New Environments
The Adult Microbiome: Stubborn but Adjustable
The study revealed that adult voles carried a legacy of their past environment in their guts. Their post-transfer gut microbiota didn't completely shift to match that of animals native to their new habitat. Instead, their microbial communities appeared to be structured by both their past and present habitats, with some features (like alpha diversity and compositional turnover) still determined by where they had lived previously 1 .
This suggests that once established, the adult gut microbiome exhibits considerable resistance to change—possibly due to priority effects where early-arriving microbes inhibit later colonists, or because the host immune system helps maintain stability.
Adult vs. Juvenile Microbiome Flexibility
Adult microbiomes show more resistance to change compared to juvenile microbiomes after environmental transfer.
Effects of Coinfection on Microbiota-Pathogen Associations
| Pathogen | Effect When Coinfection Overlooked | Effect When Coinfection Accounted For |
|---|---|---|
| Anaplasma phagocytophilum | Same association with β-diversity | Same association with β-diversity |
| Borrelia burgdorferi | Misleading pattern | Different, more accurate pattern |
| Babesia microti | Misleading pattern | Different, more accurate pattern |
| Puumala orthohantavirus | Misleading pattern | Different, more accurate pattern |
Effects of coinfection on gut microbiota-pathogen associations 8 9
The Offspring Microbiome: Surprisingly Adaptable
In striking contrast to the adults, researchers found no evidence that the maternal past habitat affected the post-transfer gut microbiota of juvenile offspring. The juvenile voles showed only a weak effect of their present habitat, suggesting their microbiomes were much more flexible and adaptable to new environments 1 .
This difference between adults and juveniles highlights the importance of life stage in microbiome development and suggests that early life may represent a critical window when microbial communities are most responsive to environmental influences.
The Coinfection Factor: Unexpected Microbial Relationships
Another fascinating study revealed that systemic pathogens (those found throughout the body rather than just in the gut) have complex relationships with the gut microbiota—relationships that are dramatically affected when animals are infected with multiple pathogens simultaneously 2 8 .
Research Insight
Overlooking coinfection status led to misleading conclusions about pathogen-microbiota associations for three out of the four pathogens studied 9 . This highlights the complexity of microbe-microbe interactions and suggests that studying pathogens in isolation may lead to oversimplified conclusions.
The Scientist's Toolkit—Decoding Microbial Communities
Modern microbiome research relies on an array of sophisticated tools that allow scientists to identify and characterize microbial communities without needing to culture each individual species (a nearly impossible task since many gut bacteria cannot be grown in laboratory conditions).
| Tool/Technique | Function | Application in Vole Research |
|---|---|---|
| 16S rRNA amplicon sequencing | Amplifies and sequences a standardized genetic region to identify bacterial taxa | Characterizing bacterial community composition in vole guts |
| ITS sequencing | Targets fungal DNA to identify fungal communities | Analyzing fungal components of the microbiome |
| Metagenome-assembled genomes (MAGs) | Reconstructs draft genomes from complex microbial communities | Identifying 254 bacterial genomes from bank vole gut microbiota 5 |
| DNA extraction kits | Isolates microbial DNA from fecal samples while inhibiting PCR inhibitors | Standardized DNA extraction for consistent results |
| Bioinformatic tools | Processes sequencing data, identifies amplicon sequence variants | Analyzing and interpreting massive sequencing datasets |
Beyond the Vole—What Microbial Relationships Mean for Ecosystems and Health
Conservation and Wildlife Translocations
The finding that past environment continues to influence the gut microbiota of translocated adults has important implications for wildlife conservation 1 .
The Holobiont Concept
Bank vole research contributes to the growing understanding of plants and animals as holobionts—complex entities composed of the host plus all of its associated microorganisms .
Future Research
Future research will explore how specific microbial taxa influence host health and adaptation, with applications in conservation and medicine.
Research Impact
"These data are relevant for decision-making in the field of conservation and wildlife translocations" 1 —a testament to how understanding small creatures can have big implications.
Conclusion: The Future of Microbiome Research
The humble bank vole has proven to be an invaluable model for understanding the complex interactions within gut microbiomes. Their varied diet, widespread distribution, and adaptability to different habitats make them ideal subjects for studying how environment, diet, pathogens, and host factors shape our internal microbial ecosystems.
As we continue to unravel the complex relationships within the gut microbiomes of bank voles and other species, we move closer to understanding the fundamental rules that govern all host-microbe systems—including our own. The wild world within these tiny rodents reminds us that we are never truly alone, but exist as complex ecosystems inhabited by trillions of microbial partners that shape our health, our evolution, and our relationship with the natural world.