Starvation is the Thread That Binds Amoebas Together

When the going gets tough, the starved huddle together en masse. You might expect this behavior from musk oxen, schools of fish or even armies of anemones. New research published in the open access journal PLoS Biology demonstrates that our spineless protistan cousins, the amoeba, seek out genetically similar relatives when they are under stress. They aggregate together to form a fruiting body which will carry their genetic information safely on when better days arrive. This happens at an expense though. Nearly 20% of individual amoebas will perish in this effort "altruistically" giving their all for their cousins. The spores of the fruiting body are hardy and will go on carrying the amoebas' genetic heritage, while some cells will die making the stalk that lifts the fruiting body off of the ground. The higher the fruiting body the more likely and farther it will be dispersed.

Figure 4: Sorting of Strains during Multicellular Development. Cells expressing either GFP or DsRed were mixed at equal proportions and allowed to develop on agar plates. Pictures were taken at the indicated developmental time points and the merged image of the two fluorophores is shown. (A) A mix of the genetically dissimilar strains AX4-DsRed and QS44-GFP shows increased segregation with time. (B) A mix of the genetically identical strains AX4-DsRed and AX4-GFP shows no segregation.

There are several interesting ramifications from this study. The amoebas must be able to detect similar genotypes. Additionally, this demonstrates an important historical point in organismal evolution. The beginnings of multicellularity. One direct hypothesis generated or supported by this is that multicellularity evolved out of a need to protect genetic information during stressful times, such as starvation. Instead of every individual slowly dying off they band together for a final push to ensure the survival of the genes.

Elizabeth A. Ostrowski, Mariko Katoh, Gad Shaulsky, David C. Queller, Joan E. Strassmann (2008). Kin Discrimination Increases with Genetic Distance in a Social Amoeba PLoS Biology, 6 (11) DOI: 10.1371/journal.pbio.0060287