Dictyostelids are very social organisms and they are also referred to as slime molds or social amoeba. They can exist as single cells in favorable conditions or form a multicellular organism when they are under stress. Dictyostelids feed on bacteria and reproduce by binary fission like amoeba (Caprette,1996). When slime molds undergo stress where there is a short supply of food, the single cells associate to form an aggregate structure called a pseudoplasmodium which consists of up to 100,00 cells. A signal chemical in the cells called cAMP (cyclic adenosine monophosphate) helps signal nearby cells to aggregate and form a multicellular structure following starvation (Flowers, 2010). This structure is able to migrate from one place to another. The pseudoplasmodium have an anterior tip and a posterior tip that helps it migrate from one place to another. These posterior and anterior ends are also sensitive to light. Response to light helps the pseudoplasmodium to contract and grow a fruiting body which have protected spores on it. Under favorable conditions that favor single cell growth, these spores can be dispersed where they can germinate and later develop through mitosis as single cells renewing the life cycle of Dictyostelium.
In sexual reproduction, in response to starvation, the cell fusion from different mating types is followed by cAMP mediated attraction of other solitary cells that are cannibalistically consumed by the diploid zygote through massive phagocytosis (Flowers, 2010). This means that the zygote feeds on the haploid cells for them to survive the harsh conditions. This association can be considered as exploitation since only the zygote only benefits from this but the haploid cells do not benefit at all from the association. Phagocytosis is the process whereby a cell engulfs other cells and later breaks it down through the help of its enzymes. This leads to the formation of a large spore in slime mold called a macrocysts. The social behavior is illustrated when the single cells are attracted to the diploid zygote to form a macrocysts (Flowers, 2010). The large spore (macrocysts) later hatches to release individual amoebae that can later undergo mitosis and the cycle begins again.
At the end of each sexual and asexual reproduction individual amoebae cells are formed which can later further divide through mitosis and if they have enough supply of food (bacteria) they can grow individually. If they do not have enough bacteria following starvation they associate and aggregate to survive in that harsh environment and so the cycle continues again.
Fig 1; Showing the sexual cycle, the social cycle and the vegetative cycle of Dictyostelium (Flowers, 2010).
Reference
Caprette, David R. “Cellular ‘Slime Molds:’ Dictyostelium and relatives.” Dictyostelium, Rice University, 27 June 1996, www.ruf.rice.edu/~bioslabs/studies/invertebrates/dicty.html.
Flowers, Jonathan M., et al. “Variation, Sex, and Social Cooperation: Molecular Population Genetics of the Social Amoeba Dictyostelium discoideum.” PLOS Genetics, Public Library of Science, 1 July 2010, journals.plos.org/plosgenetics/article?id=10.1371%2Fjournal.pgen.1001013.
