When the food supply dries up, solitary Dictyostelium discoideum cells congregate into a spore-producing tower.
Credit: Owen Gilbert/Rice University
HOUSTON: Even the simplest of social creatures - single-celled amoebae - have the ability to recognise family members and selectively discriminate in favour of them, a new U.S. study shows.
Published in a recent issue of the British journal, Nature, the study provides proof of the surprisingly sophisticated social behaviour of microbes, which have been shown to exhibit levels of cooperation more typically associated with animals.
"By recognising kin, a social microbe can direct altruistic behavior towards its relatives," said Natasha Mehdiabadi of Rice University in Texas, lead author of the study.
Recognising family members and discriminating in favour of them is a common trait among animals - be they chimpanzees, squirrels, paper wasps or business leaders. While scientists have repeatedly documented cases of kin recognition, this study is among the first to document the more sophisticated trait of kin discrimination in a social microorganism.
Mehdiabadi and colleagues at Rice University in Texas based their study on the social life of single-celled Dictyostelium purpureum, a common soil microbe that feeds on bacteria. In the wild, when food runs short, D. purpureum aggregate together by the thousands, forming first into long narrow slugs and then into hair-like fruiting bodies.
Resembling miniature mushrooms, these fruiting bodies consist of both a free-standing stalk and the spores that sit atop it. Ultimately, the spores are carried away, usually on the legs of passing creatures, to start the life cycle all over again. But in order to disperse the spores, some of the colony's individuals must sacrifice themselves to form the stalk that gets left behind.
The researchers sought to find out whether D. purpureum discriminate by preferentially directing this altruism toward their relatives.
In the study, wild strains of D. purpureum were cultured in dishes in the laboratory. For each of 14 experiments, a pair of strains were placed in a dish in equal proportion, and one of the strains in each pair was labeled with a fluorescent dye.
Food was withheld, causing the microbes in each dish to form dozens of slugs and fruiting bodies. Upon observing their social development, the team found that individual fruiting bodies contained predominantly one strain or the other.
"Our experiments ruled out potential differences in developmental timing and showed that these organisms preferentially associate with their own kin," said Joan Strassmann of Rice University, co-author of the study.
It's unclear how D. purpureum distinguishes relatives from non-relatives, but Mehdiabadi said the process likely relies on a genetic mechanism.
With Rice University
