amoeba blog

Social Amoeba: Dictyostelium discoideum and other DictyostelidsThe study of group-living organisms, like the social insects, has provided a wealth of insights into social evolution. Nonetheless, empirical work on these complex systems is limiting, or at the very least challenging, with regard to insights into the molecular or genetic mechanisms underlying cooperation and exploitation. Thus, more progress might be made by studying altruism at another level. Recent work has demonstrated the unrealized potential of a microbial system in the study of social evolution. The cellular slime molds of the Dictyostelidae possess an unusual developmental cycle. When starved, individual amoebae aggregate to form a multicellular fruiting body in which some cells give up reproduction and become sterile stalk cells that aid in the dispersal of the fertile spore cells. Recent work has shown in nature that genetically distinct clones of the social amoeba, Dictyostelium discoideum, can mix to form chimeras, and sometimes, one clone can exploit the other by contributing less than its proportional share to the sterile stalk (Strassmann, Zhu, & Queller 2000, Nature 408: 965-967). I propose to explore whether exploitation occurs in other dictyostelid species and whether natural variation across species in the expression patterns of genes known to affect spore/stalk allocation is important in cheating. Identifying the gene or genes involved in exploitation will be a major advance. Elucidation of the costs and benefits of chimerism across the social amoebae will increase our understanding of the origins of multicellularity, the costs of chimerism, the genetic mechanisms of exploitation, and the evolutionary history of this important social trait. Thus, these micro-organisms, have great promise in providing a powerful laboratory system for a deeper understanding of social evolution.