Glossary

Floral nectar is colonized by yeasts and bacteria that alter its chemistry — shifting sugar concentrations, amino acids, and volatile compounds. Pollinators often respond to that shift, sometimes favoring microbe-colonized flowers and sometimes avoiding them.

The effect can go either way. As microbes feed on the nectar’s sugars, they give off their own byproducts — and some of those byproducts smell or taste off-putting to pollinators, or even damage the pollen so it can’t fertilize the next flower. Other microbes give off byproducts that smell sweeter or richer, making the flower even more inviting. It’s not that some microbes help and others harm on purpose — it’s just a side effect of what they release as they grow, and which way it tips depends on which microbes move in.

Researchers studying a related hummingbird-pollinated shrub, Bush Monkey Flower (Diplacus aurantiacus), describe each flower as its own small island — microbes move in, compete with each other for the nectar’s sugars, and get carried off to the next flower by whatever hummingbird or insect stops by.

Zoom out across many flowers and many seasons, though, and this stops looking random. A plant’s nectar chemistry is something it passes on to its offspring, and that chemistry shapes which microbes tend to move in and how attractive the flower ends up smelling or tasting. Flowers whose nectar happens to favor a more appealing microbial mix get pollinated more often, produce more seed, and pass that nectar chemistry on to the next generation. Over time, this becomes a quiet, invisible form of natural selection — pollinators aren’t just choosing flowers; they’re steering which nectar chemistry survives into the future.

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