Dense clouds of starlings dip and soar, congregating in undulating curtains that darken the sky; hundreds of thousands of wildebeests thunder together across the plains of Africa in a coordinated, seemingly never-ending migratory loop; fireflies blink in unison; entire forests of bamboo blossom at once. Scientists have studied these mesmerizing feats of synchronization for decades, trying to tease apart the factors that enable such cooperation and complexity.
Yet there are always individuals that don’t participate in the collective behavior — the odd bird or insect or mammal that remains just a little out of sync with the rest; the stray cell or bacterium that seems to have missed some call to arms. Researchers usually pay them little heed, dismissing them as insignificant outliers.
But a handful of scientists have started to suspect otherwise. Their hunch is that these individuals are signs of something deeper, a broader evolutionary strategy at work. Now, new research validating that hypothesis has opened up a very different way of thinking about the study of collective behavior.
Early clues emerged after Corina Tarnita, a mathematical biologist at Princeton University, and her colleagues turned their attention to the cellular slime mold Dictyostelium discoideum. Typically, it lives as a collection of solitary amoebas, with each cell eating and dividing on its own. But when threatened with starvation, up to a million of those cells can coalesce into a mushroom-like tower. Around 20% of them create a stalk, sacrificing themselves so that the rest can move to the top of the structure and form spores, which can last for months without food. Ultimately, water and wind disperse those spores to new and potentially more nutrient-rich environments.
Scientists have used slime molds to experimentally investigate the emergence and maintenance of social behavior, identifying mechanisms that ensure cooperation among the amoebas. But they’ve always focused on the aggregated cells. Tarnita and her team wanted to investigate whether the cells that stayed behind — the “loners,” as they called them — also played an important role. [Continue reading…]