News: One Way Climate Change May Cut Animal Lives Short — Messing with Gut Microbes

As headlines focus on melting glaciers and rising water levels caused by global warming, climate change is quietly taking its toll on the nearly invisible occupants of this planet, the microbes.

In a study published in the journal Nature Ecology and Evolution, researchers from the University of Exeter and the University of Toulouse wrote that "climate change is now considered to be the greatest threat to biodiversity and ecological networks, but its impacts on the bacterial communities associated with plants and animals remain largely unknown."

To look more closely at the relationship between a warming climate and gut microbes, scientists chose the common lizard — a widely-distributed Eurasian lizard, Zootoca vivipara — to investigate the impact of environmental warming on ectotherms.

Ectotherms are cold-blooded animals like snakes, lizards, amphibians, and fish that depend on their environment to maintain their body temperature. Strictly speaking, these animals do not have "cold-blood," but use activity to keep a constant temperature. Turtles, lizards, and snakes all bask in the sun to moderate their core temperature.

Because their metabolic processes depend on the environment, climate change can have real impacts on these animals. To study what might happen as temperatures rise, the research term developed an experiment that divided 241 adult lizards and 365 juvenile lizards caught in the Cevennes mountains of France.

In captivity, the lizards were mixed and released into nine different semi-natural enclosures representing three climate ranges including present climate, intermediate, and warm climate (an increase of 2 to 3 degrees Celcius). The intermediate habitat offered a look at how microbes in lizards might transition into a warmer environment.

For one year, the lizards lived and adapted to these conditions. After that time, scientists took microbial samples from the lizards that survived — 92 adults and 73 yearlings. Samples were taken from the vent of the lizards, which offers a good representation of the microbes in the hind parts of the animals. Researchers used DNA sequencing and molecular and statistical analysis to come to their results.

While it may seem a stretch to be looking at bacteria from the backends of lizards to make findings of environmental consequence — that is just what these researchers did.

[O]ne of the most intricate symbiotic relationships is probably that between animal hosts and the bacterial community inhabiting their guts.

The microbes that reside within and on our bodies are our closest neighbors. Understanding how the environment impacts the microbial community of an animal of any kind could have a "canary in the coal mine" message for humans. Here are the findings from the study:

• Warmer climates had a "strong negative effect" on the "bacterial richness" of individual lizard gut communities. Complete communities of beneficial bacteria were not wiped out, but their numbers declined by 34 percent.
• Different bacterial families fared better in different climatic settings. Proteobacteria were more abundant in warmer climates while Bacteroidetes and Firmicutes were higher in number in the present climate. These bacterial families are all microbe communities in the human gut. In humans, Proteobacteria include many pathogens including E. coli, Salmonella, Heliobacter, Vibrio, and other less savory characters that do significant harm outside of the gut environment.
• Overall, populations of types of Proteobacteria increased with the temperature, and numbers of different types of Firmicutes and Bacteroidetes decreased.
• In observing the lizards in this experiment for an additional year, the lizards living in the "present" climate with greater bacterial richness correlated with an additional year of survival.

"[O]ur research shows that a relatively small rise in temperature can have a major impact on the gut bacteria in common lizards," said Elvire Bestion, at the University of Exeter, in a press release.

Noting the need for more research to confirm these ominous findings, the authors commented on the changes to the lizards throughout the experiment, noting in particular:

• Greater microbial diversity in the gut is generally seen as beneficial. Loss of diversity and microbe community numbers due to climate warming could be detrimental.
• The types of gut microbe families that declined were types that are important to reptiles. Associated with metabolism and cellular signaling, the loss of these bacteria is not a gain for the animal.
• The research team could not say absolutely how these changes occur. For example, changes in the climate could result in shifts in the food supply, mating habits, different contexts for exposure to communities of bacteria, or climate-related damage that targets the lizard itself.

This research takes a step off the beaten path to examine the big changes that are happening to some of the smallest creatures around — microbes and lizards that they inhabit. Though the need for follow-up research is clear, this research adds to a growing body of knowledge about what could be in store for all of us as our planet continues to warm.

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