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Evans and Fitzpatrick Publish Research on Trinidadian Guppy Gut Microbiome in "Proceedings of the Royal Society B."

On the list of scientific tools that help us understand health, evolution or the environment, the Trinidadian guppy doesn't often come to mind. The fish are more often thought of as aquarium pets in the U.S. and, in their native Trinidad, wild guppies are so ubiquitous, they’re almost taken for granted.

Thanks to a unique combination of biology and ecology, the guppies have provided researchers with insights into evolution for decades. Evans and Fitzpatrick have pushed those insights a step further, showing the guppies’ potential to help probe big questions about how microbes living in host organisms contribute to health, survival and quality of life.

As scientists learn more about the gut microbiome — the collection of microbes that lives in a host organism’s digestive tract — it’s becoming increasingly clear that it plays an important role in the well-being of its host. In fact, human health is intimately tied to our gut microbiome. 

Evans and Fitzpatrick are interested in some of biology’s big-picture questions and wanted to better understand how microbiomes change as organisms evolve. They wanted to better investigate what are the biggest drivers of microbiomes as host organisms evolve. It could be things like gut shape, diet or characteristics of a new environment, which is likely to contain microbes that are foreign to the host.

In the 1950s, evolution researchers realized that they could take guppies from one ecosystem where the fish had lots of natural predators and put them in another where they didn’t. Over time, the genes and traits of the fish would adapt to reflect the native populations in those low-predator environments. Likewise, fish transferred from low-predation sites would adapt when transferred to streams with high numbers of predators.

“And it’s repeatable. They evolve in many of the same ways almost every time,” Evans said. “That’s why this system is in textbooks.”

“Given that we know guppies evolve really fast in parallel ways, we could ask how does the microbiome change as guppies evolve,” Fitzpatrick said.

They returned to the same sites where scientists used to study guppy evolution to instead sample the microbiome of native fish as well as transplanted populations. Going to more than a dozen different sites, they sampled fish lineages that had been transplanted as recently as five years ago and others that were moved closer to 60 years ago.

Working with Brazilian experts from Rio de Janeiro State University, they found that the guppies’ microbiomes changed in response to their environment much faster than their genes and physical traits. The shape of guppy guts, which drives what types of microbes survive there, also changed more quickly than expected.

Yet, unlike the genes and traits of transplanted fish descendants, their gut microbe populations did not end up matching those found in the fish native to a particular environment. Despite the mismatch, though, the function of the microbiomes was similar. That is, transplanted fish lineages had different microbes that were essentially doing the same thing as native ones.

Evans and Fitzpatrick concocted the idea for this study years ago, when they were both postdoctoral researchers. It was spontaneous idea, but one that would combine the strengths of Evans, an expert in microbiology, and Fitzpatrick, an expert in evolutionary ecology.

The two went to Trinidad to collect samples in 2014 and, at the time, it was a side project. Since then, they’ve been starting up their own research labs at MSU, making it tricky to find time to complete the project — a challenge that was further heightened during the COVID-19 pandemic.

Now, they’ve published the research in a special issue of Proceedings of the Royal Society B, which is featuring the work of those affected by the coronavirus, especially women and caretakers.

“We were really glad to support this special issue,” Fitzpatrick said. “Three of the four authors are women with children.”