Scientists have discovered that a one-celled slime mold once thought to be a strict hunter, may actually be nature’s smallest farmer. According to findings published in Nature, researchers in Texas have found that some of the soil-dwelling amoebae carry around bits of bacteria in their reproductive structures that they will use as seeds, planting a new crop when food gets scarce. About a third of the slime molds (Dictyostelium discoideum) studied exhibit this behavior, which scientists are calling ‘bacterial husbandry.’
Previously, scientists believed the amoebae were strictly single-celled hunters. However, the slime molds came into fame for their ability to combine together in times of food shortage. When food is plentiful, they’ll reproduce on their own, but when an area is dried up, tens of thousands of Dictyostelium will combine together to form a giant slug-like super slime mold.
The giant slug, known a motile pseudoplasmodium, will then find a suitable environment and morph itself into a standing stalk with a big spore at the top. The weaker cells move to anchor the bottom, sacrificing themselves and helping the stalk morph the spore into a “Mexican hat”-like disc and release it into the air. When it lands, far away, the Dictyostelium break apart and start anew, hopefully thankful that thousands of their cousins died so they’d have another chance at life. The farmers of the group then release their stored bacteria, giving the new pilgrims a source of food in the strange new place. This process is detailed in a fascinating episode of Radiolab about friendship in the animal kingdom.
However, these crazy new farming variety of Dictyostelium have some drawbacks. Because they store food (bacteria) in their reproductive structures, they produce fewer offspring. They also tend to travel shorter distances than those who strictly hunt for their meals. Unfortunately, their farming is quite primitive, and very different from any recognizable human form of farming. Mostly, they release some bacteria, let it develop a bit, and then eat most of it.
Many questions remain. Researchers would like to test the genetic differences between hunting and farming single-celled slugs and figure out what genes cause this change in behavior. Still, the slime molds are a social species that desire to pass along their genetic code (much like us), making us wonder if that trait plays a large role in the formation of a sacrificial quality like farming.
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