WHAT DO WE KNOW ABOUT MICROBES AND ANIMAL PHYSIOLOGY?
Scientists have recently learned about a hidden world of microorganisms, or microbes, that may control a lot of human and animal physiology, or the ways in which our body functions. Microbes promote human health, yet it remains undiscovered how microbes help animals in the wild. This backgrounder highlights scientific understanding of how microbes influence seasonal events in wild animals, such as hibernation and migration, and explains how scientists are tackling this new and exciting frontier.
HOT RESEARCH QUESTIONS
1. IS THERE A REGULAR PATTERN OF HOW THE ANIMAL MICROBIOME CHANGES WITH THE SEASONS? IS THERE A MIGRATORY MICROBIOME?
2. DOES THE MICROBIOME FACILITATE SEASONAL CHANGES IN HOST DIET, PHYSIOLOGY, OR BEHAVIOR? DO MICROBES AID HIBERNATING AND MIGRATING ANIMALS?
3. HOW ARE THE SHIFTING GUT MICROBIOME COMMUNITIES POPULATED? WHAT PROPORTIONS OF MICROBES ARE INHERITED FROM HOST PARENTS? ARE NEW MICROBES INTRODUCED THROUGH DIET AND MATING?
Studying the patterns of microbial change in humans is difficult because there aren't many populations that rely exclusively on seasonal foods or are willing to exercise while keeping all other daily activities controlled. Instead, scientists are turning to wild animals to investigate these questions, because animals and their microbes consistently experience fluctuating conditions, such as diet and activity levels, on an annual basis. As in humans, microbes in wild animals aid in the survival of their host through shifting environments by controlling aspects of their physiology.
Sidebar: How to identify the microbes living within you
Microbiota is the collection of microorganisms living within a host, and the microbiome is the collection of their genomes (DNA) or transcriptomes (RNA). Scientists use sequencing techniques–a series of steps to extract and isolate genetic material–to identify the specific DNA and RNA combinations that identify a microorganism. Over the last decade, sequencing techniques have become affordable and time-efficient, enabling scientists to characterize the number and types of microorganisms that make up an animal's microbiome. To get a clearer picture about how the microbiome functions within a host, researchers are beginning to manipulate specific variables, such as diet, and sequence RNA samples to identify the microbes present and determine how they respond.
Other animals, like the Blackpoll Warbler, enact an opposite survival strategy, where they increase their activity to migrate to southern latitudes in search of more abundant food resources. Remarkably, the Blackpoll Warbler flies for up to five days without stopping during migration. These migratory flights burn most or all of the birds’ fuel stores and reduce the size of their digestive organs. Migrating songbirds must stop along their migration to first rebuild their digestive tracts and then take advantage of ripe fruits to quickly pack on body fat to continue their journey. A typical migratory songbird punctuates short, energy-intense flights with these longer periods of resting and refueling at stopover sites, so birds must be able to change their bodies on shorter timescales than hibernators.
The return of spring thaws frozen grounds and provides resources needed for hibernating animals to emerge and songbirds to return to temperate areas. An animal’s microbiome most likely exists along a spectrum of assistance, where it plays an active role in helping its host through these changes, or, less likely, it is merely a passenger along for the ride.
Recent studies suggest that microbes are changing across a bird's annual cycle. Swainson’s Thrushes and Gray Catbirds, two common migrants in North America, have gut microbiota composed of very different species during spring migrations versus fall migrations. This shift likely results from the birds’ exposure to different food sources, such as greater availability of fruits than insects during fall versus spring migration. Additionally, actively migrating shorebirds have higher numbers of a particular bacterial genus (Corynebacterium) as compared to non-migrating shorebirds. The cause underlying changes to the microbiome and how these changes affect migrating birds, however, is still a mystery.
Created with images by Clara Cooper-Mullin • SK Yeong - "Eurasia Tree Sparrow" • ractapopulous - "bird owl eyes" • homecare119 - "bird wings fluttering"