  Within the context of evolution, an altruistic act that benefits the
receiving individual at the expense of the acting individual is a puzzling
phenomenon. An extreme form of altruism can be found in colicinogenic E. coli.
These suicidal altruists explode, releasing colicins that kill unrelated
individuals, which are not colicin resistant. By committing suicide, the
altruist makes it more likely that its kin will have less competition. The
benefits of this strategy rely on the number of competitors and kin nearby. If
the organism explodes at an inopportune time, the suicidal act may not harm any
competitors. Communication could enable organisms to act altruistically when
environmental conditions suggest that that strategy would be most beneficial.
Quorum sensing is a form of communication in which bacteria produce a protein
and gauge the amount of that protein around them. Quorum sensing is one means
by which bacteria sense the biotic factors around them and determine when to
produce products, such as antibiotics, that influence competition. Suicidal
altruists could use quorum sensing to determine when exploding is most
beneficial, but it is challenging to study the selective forces at work in
microbes. To address these challenges, we use digital evolution (a form of
experimental evolution that uses self-replicating computer programs as
organisms) to investigate the effects of enabling altruistic organisms to
communicate via quorum sensing. We found that quorum-sensing altruists killed a
greater number of competitors per explosion, winning competitions against
non-communicative altruists. These findings indicate that quorum sensing could
increase the beneficial effect of altruism and the suite of conditions under
which it will evolve.
