Discuss the maintenance of altruism in the social amoeba Dictyostelium doscoideum - Essay Example

The separation of cheaters reduces the occurrence of cheating by the high genetic relatedness selection of cheaters according to the Kin-selection theory. In the social amoeba Dictyostelium Doscoideum which occurs in soil samples, the relatedness in natural groups is high enough to prevent the spread of destructive social cheaters. High relatedness can control a mutant that would otherwise at low relatedness destroy cooperation. The importance of relatedness is however challenged by the life cycle of social amoeba in the selection to prevent cheating.

The altruism of amoeba is featured in the death of some amoeba to ensure the survival of the majority. When the bacterial source of food of amoeba that are naturally solitary organisms is depleted, they aggregate themselves to form a multicellular fruiting body where 25% of the cells die to form a stem that raises the remaining cells high enough for dispersal (Gilbert et al, 2007). The mixture of different clones creates the opportunity for cheaters and co-operators to form the group where they can cheat each other, for example in avoiding creating the stalk.

Gilbert et al (2007) used mechanisms such as the estimation of relatedness in nature, searching for cheater mutants in nature and the examination of the cheating advantage of the fbxA . The relatedness is high in the co-operative groups of Dictyostelium Doscoideum since the organism forms fruiting bodies more often with organisms of the same kin. Fruiting bodies that were observed 92% were found to be of one clone (Gilbert et al, 2007). The high level of relatedness reduced the opportunity of cheaters gaining by avoiding forming the stalk which would be costly to the survival of the cells.

The socially disruptive cheating mutant fbxA which cheats in chimeras was found to produce little or no spores on its own and hence it would be disastrous if allowed to spread. It would spread at low relatedness to reduce co-operation in the normal fruiting of cells and reduce the formation of spores which could result in extinction. Similarly, the mutant dimA­? is a social defector that fails to react to the signals to become part of the sterile stalk. The pleiotropic effect due to high relatedness of cells which occurs late during their development discourages cheating hence the dimA­?

is usually unsuccessful. According to Khare et al (2009), some of the mechanisms that can be used to restrain cheating behaviour in nature include lowering the fitness of the cheater by intrinsic selection, pleiotropy of the cheater gene, the high genetic relatedness in natural populations, discrimination on the basis of kin as well as the evolution of the resistance to cheating. This is applied by a population of mutations that are able to resist cheating but this evolution is disadvantageous since it could result in new cheating strategies that could result in the demise of co-operation in these populations.

In the research to find out whether it was possible to yield mutants that could resist cheating and still remain co-operative, Khare et al (2009) mixed different mutated cells and allowed them to develop into fruiting bodies and spores. They found that in a natural population of Dictyostelium Doscoideum the wild type allele was replaced during the development of the cells by a mutation that were predicted to be resistant to cheating. They also mixed wild type cells and mutant cells with cheater cells in a ratio 1:1 to