Altruism, selfishness, and heterocytosis in cellular slime molds

Abstract

The cellular slime mold, Dictyostelium discoideum, undergoes a developmental cycle, with originally independent amoeboid cells aggregating and differentiating into a multicellular fruiting body. Sociobiological theory indicates that amoebae becoming nonreproductive stalk cells are sacrificing their individual fitness on behalf of the spore cells. Spore cell success and relatedness to stalk cells should be providing inclusive fitness benefits which override the individual fitness cost to the stalk cells. Two pure cultures of D. discoideum and a mixture of these cultures were grown under conditions inducing fruiting-body formation, and the ratios of spore capsule diameter to stalk length were determined. The mixed culture possessed a significantly larger spore capsule diameter relative to the stalk length (and thus a higher spore:stalk ratio) than either pure culture. Cellular slime mold amoebae display less altruistic behavior when forming a fruiting body along with less-related amoebae.