An amoeba who raises bacteria crops is the world's tiniest farmer

Humans like to think we invented agriculture, but a single-celled organism might have us beaten by several million years. An amoeba species known as "Dicty" finds bacteria, moves them to the best location, and harvests them like crops.

Dicty, short for D. discoideum, is a pretty amazing creature. It's what known as a social amoeba, which means that, after the creature has used up all the food resources in its territory, it clumps together with a bunch of its relatives to form a half-centimeter-long slug-like creature. This slug-like mega-organism then starts looking for bacteria-rich areas where the amoebas can continue to feed. Once there, the slug becomes gets to reproducing, turning into what's known as a fruiting body. This body then releases a bunch of spores that spawn the next generation of amoebas.

That's awesome enough, but a researcher recently discovered totally unexpected about Dicty. While working with spores from a collection of wild amoebas, Rice University researcher Debra Brock noticed bacteria were lurking around the fruiting body. Brock thought these might be an infection, so she gave the amoebas antibiotics and moved the now bacteria-free fruiting body to a new area. The spore clones immediately went out on this new bacteria patch and brought back lots of the little guys, as though they were actively gathering them up.

Later experiments showed the amoebas were effectively planting the bacteria, as Brock explains:

"They can carry [the bacteria], they disperse them, and they seed them in new places, and they actually harvest. We felt that was sufficient to be designated a farmer."

Much like in human history, farming was far from universal and carried with it some serous pros and cons. Only about a third of the amoeba displayed the farming behavior, indicating it's a moderately useful adaptation but not so successful that it's taken over the entire species. Farming was very useful when the bacteria-carrying amoeba arrived at a spot with very little bacteria, as they had an instant resource advantage. But non-farmers did better in areas with plenty of bacteria, as the farmers wasted time harvesting when they could have just gone straight to eating.

Dicty is the world's smallest farmer, but it isn't the only non-human agriculturalist. There are fungus-growing ants and termites, algae-farming damselfish, and snails that work with fungus. But Dicty is the first microbe, which suggests a surprising universality to farming behavior. Evolutionary biologist Bernard Crespi praises Brock's discovery, and says we may even be able to illuminate aspects of humanity's farming history based on our work with Dicty:

"It's a wonderful paper. It really is the first data that's out there, so there's always going to be questions. You're always looking for convergences [in evolutionary biology]. Slime molds and humans is one of the more unusual comparisons."

[Nature via ScienceNOW]