Kin Discrimination and the Social Amoeba

Research recently published in PLoS Biology indicates that amoebas which are close to starvation will seek out genetically similar relatives.

We tested how widely social amoebae cooperate by mixing isolates from different localities that cover most of their natural range. We show here that different isolates partially exclude one another during aggregation, and there is a positive relationship between the extent of this exclusion and the genetic distance between strains. Our findings demonstrate that D. discoideum cells co-aggregate more with genetically similar than dissimilar individuals, suggesting the existence of a mechanism that discerns the degree of genetic similarity between individuals in this social microorganism.

It will be really interesting if/when a description of the mechanism discerning genetic similarity is given, and if there is any remnant of it still present in humans or to what extent it exists in other species.

Interestingly, this study seems to provide more evidence for the gene being the important unit of selection by nature. It is the very survival of these organisms that could explain what has been observed here on a genetic level: genes which are similar have evolved a mechanism for detecting one another because of the mutual (but ultimately selfish) benefit of doing so. The further from similarity they are, the more likely they are to discriminate in offering assistance, as was the case in this study. Aside from the reason of promoting different allelic versions of one’s self, one good reason for the evolution of this discrimination mechanism would be to weed out “cheaters”, or genes which take advantage of the ‘altruism’ of these genes to assist other amoebas in their time of need (starvation) by abusing their helpful nature. That is, if it is embedded in me, when I see a fellow organism of my species, ‘If starving, help fellow organism’, it will pay me to also have the command, ‘If distantly related, do not help’. In other words, if I see my brother and my 2nd cousin starving, it’s going to be worthwhile for my genes if I am able to detect which one is my brother since he shares more genetic material with me than my 2nd cousin. By helping him instead of the more distant relative, I am increasing the odds that my genes or genes very close to my own will be passed on to the next generation. My genes have limited interest in helping out other, distant genes.

By the by, the use of GFP makes this experiment all the more beautiful.