David Gray / Reuters

In the spring of 2015, two-thirds of all the world’s saiga antelope dropped dead. Around 200,000 of these quizzical, endangered animals perished without any warning, over a 65,000-square-mile stretch of Mongolia. Now, Eleanor Milner-Gulland from the University of Oxford and her colleagues think they know why. As I reported earlier this year, they suspect that an extreme combination of heat and humidity affected a bacterium that normally lives harmlessly in the saiga’s body. In the unusual climate, this microbe turned renegade, invading the saigas’ bodies and causing fatal cases of blood poisoning.

The saiga’s woes offer a glimpse into a troubling future. Every animal and plant exists in partnership with microbes that live in and on its tissues and organs, but these partnerships aren’t inherently beneficial or harmonious. They are often held together by fragile sets of circumstances, and many of them could turn sour in a warming world.

When oceans get too hot, for example, corals expel the microscopic algae that live within their tissues and provide them with nutrients. Without these partners, the corals lose their resplendent colors, starve, and eventually die. But Nancy Knowlton from the Smithsonian Museum of Natural History recently showed that even when the algae aren’t evicted, they seem to keep the nutrients they produce for themselves, at the expense of their coral hosts. Warming water shoves these beneficial microbes towards a more parasitic way of life.

Between 10 and 15 percent of insect species also depend on bacteria for nutrients that are missing from their diets. Without these microbes acting as living dietary supplements, aphids couldn’t survive on plant sap, bed bugs couldn’t thrive on blood, and carpenter ants couldn’t live on a vegetarian diet. But many of these symbiotic bacteria are exquisitely sensitive to high temperatures. If it gets too hot, they die, as do their insect hosts. This calamity, which Jennifer Wernegreen calls “mutualism meltdown,” might stop insects from adequately adapting to climate change.

It’s not all bad news, though. By learning more about the relationships between bigger species and their microscopic companions, we may be able to deliberately engineer new partnerships that can take the heat. For example, some scientists are trying to pair corals with heat-resistant strains of algae to see if they fare better in hotter water.

Meanwhile, Rusty Rodriguez and Regina Redman from Adaptive Symbiotic Technologies, a Seattle-based startup, are trying to pair crop plants with heat-tolerant fungi that could help them to tolerate heat, drought, salt, and other challenging environments. You can see the inspiration behind their work in the video below—the ninth in a series of online films produced by HHMI Tangled Bank Studios, which adapt the stories in my book, I Contain Multitudes.

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