An invitation to die: initiators of sociality in a social amoeba become selfish spores

Abstract

Greater size and strength are common attributes of contest winners. Even in social insects with high cooperation, the right to reproduce falls to the well-fed queens rather than to poorly fed workers. In Dictyostelium discoideum , formerly solitary amoebae aggregate when faced with starvation, and some cells die to form a stalk which others ride up to reach a better location to sporulate. The first cells to starve have lower energy reserves than those that starve later, and previous studies have shown that the better-fed cells in a mix tend to form disproportionately more reproductive spores. Therefore, one might expect that the first cells to starve and initiate the social stage should act altruistically and form disproportionately more of the sterile stalk, thereby enticing other better-fed cells into joining the aggregate. This would resemble caste determination in social insects, where altruistic workers are typically fed less than reproductive queens. However, we show that the opposite result holds: the first cells to starve become reproductive spores, presumably by gearing up for competition and outcompeting late starvers to become prespore first. These findings pose the interesting question of why others would join selfish organizers.

Wild Dictyostelium discoideum social amoebae show plastic responses to the presence of nonrelatives during multicellular development

“…discoideum . We considered two previous hypotheses with opposite predictions: (a) cells in chimeras race to become spores (Kuzdzal‐Fick, Queller, & Strassmann, ) and (b) discoordination due to mixing two genotypes slows down development (Hirose et al, ). We compared the gene expression patterns of our samples to a developmental time series from the axenic laboratory strain AX4 (Rosengarten et al, ) and tested whether there was a consistent difference by social condition that may hint toward a relative acceleration or delay in development in chimeras.…”

Evolution of cooperation and control of cheating in a social microbe

“…In the first experiment, cells were put into nutrient-free medium 4 h apart. Those with the 4-h head-start in the social stage preferentially became spores (74). The other experiment used a knockout that was incapable of initiating aggregation but was capable of responding to the initial signal from others and relaying it (75).…”

Cell condition, competition, and chimerism in the social amoebaDictyostelium discoideum

“…This condition-dependence may be mediated by differential sensitivity to DIF-1, an intercellular signal molecule that directs cells to differentiate into a major subtype of pre-stalk cells THOMPSON & KAY 2000a, 2000b. A counter example to glucose-grown cells becoming spores is that the first cells to starve become spores, possibly because they reallocate intra-cellular resources for competition even though they are generally weaker because they starved earlier (KUZDZAL-FICK et al 2010).…”