Healthcare (Commonwealth Union) – For most individuals, natural selection is the process in which organisms with advantageous traits are more likely to survive and reproduce, passing those beneficial traits on to the next generation. Over time, this causes a species’ genes and behaviours to shift in response to its surroundings.
Although these changes typically unfold over many generations, a research group led by Taichi Suzuki — a joint assistant professor at Arizona State University’s Biodesign Institute and College of Health Solutions — discovered that simply transferring a mammal’s microbiome can influence behaviour within a relatively short timeframe. In just four generations, this transmission produced a new inheritable trait without any change to the animals’ genetic code.
The study, published in Nature Communications and carried out with scientists from the Max Planck Institutes, Rutgers University and Cornell University, explored how artificial selection acts on both an animal and its microbiome — an area Suzuki says is gaining attention in evolutionary biology and domestication research.
To investigate whether selection-driven shifts in mammalian physiology or behaviour could arise solely from changes to the microbiome, Suzuki and his colleagues used mice and monitored their movement patterns.
“To identify which aspects of physiology or behavior were most influenced by the microbiome, we performed fecal transplant experiments using two distinct microbiomes and compared a wide range of traits in germ-free mouse recipients,” he explained. “To our surprise, behavior — especially activity level — showed the strongest microbial influence, far exceeding effects on morphological traits such as body weight or size.”
The researchers discovered that mice given microbiomes from donors with low activity levels also became less active. One microbe was especially noteworthy: Lactobacillus.
Suzuki indicated that they found that a compound made by Lactobacillus, called indolelactic acid (ILA), plays an important role in shaping behavior.
He further stated that even though ILA does not easily enter the brain, it can influence mood, movement and behavior indirectly by calming the immune system and reducing inflammatory signals that reach the brain.
This link between gut bacteria and behavior is known as the gut–brain axis.
Suzuki’s findings provide something unusual—clear experimental proof that shifts in behavior due to the selection can be driven entirely through the transfer of microbes.
He further indicated that there are many evolutionary theories that propose the microbiome plays a part in adjusting to rapid atmosphere and climate changes and added that the work gives experimental backing for those ideas.
In the wild, the worldwide expansion of house mice illustrates this idea at work.
Suzuki indicated that house mice travelled alongside people from Western Europe to the Americas during the last two centuries.
He further pointed out that even within this relatively brief evolutionary window, mice in the Americas have already begun to adapt, showing variations in their size and behavior depending on whether they inhabit colder or warmer regions.
His researchers showed that some of these behavioral shifts can arise purely through selecting certain microbiome communities.
He stated that they showed that high-activity behavior, characteristic of ancestral mice from Western Europe (possibly reflecting elevated metabolic demands in cooler climates), can alter low-activity behavior, which is witnessed in warm-climate populations such as Brazil and simply by choosing mice with lesser activity and sending the microbiome across four generations.
The results of the study indicate that adaptations driven by the microbiome could enable animals — and possibly humans — to cope with fast-moving environmental shifts much more quickly than genetic changes alone would permit.
Suzuki’s research group is currently examining 16 wild rodent populations across Arizona’s “Sky Islands” to explore how variations in microbial communities contribute to adaptation in natural habitats.
The potential impact reaches beyond evolution and environmental adjustment, with applications in biotechnology and healthcare as well.
