• AMOTZ ZAHAVI

      Articles written in Journal of Biosciences

    • An individual-level selection model for the apparent altruism exhibited by cellular slime moulds

      AMOTZ ZAHAVI KEITH D HARRIS VIDYANAND NANJUNDIAH

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      In Dictyostelium discoideum, cells that become part of the stalk or basal disc display behaviour that can be interpreted asaltruistic. Atzmony et al. (Curr Sci 72:142–145, 1997) had hypothesised that this behaviour could be the outcome of anadaptive strategy based on differing intrinsic quality as reflected by phenotypes that indicate differences in potential forsurvival and reproduction, followed by intercellular competition among amoebae of differing qualities. Low-qualityamoebae would have a poor chance of succeeding in the competition to form spores; they could enhance their chances ofsurvival by adopting a presumptive stalk strategy. Here we extend the hypothesis by making use of recent findings. Ourapproach is based on the view that an evolutionary explanation for the apparent altruism of stalk cells in D. discoideummust apply broadly to other cellular slime moulds (CSMs) that exhibit stalk cell death. Further, it must be capable of beingmodified to cover social behaviour in CSMs with an extracellular stalk, as well as in sorocarpic amoebae whose stalk cellsare viable. With regard to D. discoideum, we suggest that (a) differentiation-inducing factor, thought of as a signal thatinhibits amoebae from forming spores and induces them to differentiate into basal disc cells, is better viewed as a mediatorof competition among post-aggregation amoebae and (b) the products of the ‘recognition genes’, tgrB and tgrC, allow anamoeba to assess its quality relative to that of its neighbours and move to a position within the aggregate that optimises itsreproductive fitness. From this perspective, all cells behave in a manner that is ‘selfish’ rather than ‘altruistic’, albeit withdifferent expectations of success.

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