A grex, (also called a pseudoplasmodium, or slug) starts as a crowd of single-celled

amoeba An amoeba (; less commonly spelled ameba or amœba; plural ''am(o)ebas'' or ''am(o)ebae'' ), often called an amoeboid, is a type of cell or unicellular organism with the ability to alter its shape, primarily by extending and retracting pseudo ...

e of the groups

Acrasiomycota The family Acrasidae ( ICZN, or Acrasiomycota, ICBN) is a family of slime molds which belongs to the excavate group Percolozoa. The name element - comes from the Greek ''akrasia'', meaning "acting against one's judgement". This group consis ...

or Dictyosteliida; ''grex'' is the Latin word for ''flock''. The cells flock together, forming a mass that behaves as an organised, slug-like unit. Before they get stimulated to crowd together to form a grex, the amoebae simply wander as independent cells grazing on bacteria and other suitable food items. They continue in that way of life as long as conditions are favourable. When the amoebae are stressed, typically by a shortage of food, they form a grex. According to species and circumstances, details of the shape of the grex and how it may form will vary but typically the stressed amoebae first produce

pheromone A pheromone () is a secreted or excreted chemical factor that triggers a social response in members of the same species. Pheromones are chemicals capable of acting like hormones outside the body of the secreting individual, to affect the behavi ...

s that stimulate the flock to vertically assemble in a column. When the column of aggregated cells becomes too high and narrow to stay upright, it topples and becomes a slug-shaped mass: the grex. The grex is mobile; in its form as a slug-like unit it can glide over a moist surface. Once it has moved far enough to complete its development, the cells of the amoebae differentiate according to their positions in the grex; some become the spore cells and the covering shell of the ''fruiting body'' near the tip, and others form structures such as the stalk. Cells forming the structural items, such as the stalk and shell, desiccate and die; only the spores in the fruiting body survive to propagate. When circumstances are right and the fruiting body is mature, its shell ruptures and releases the spores. The spores then may be transported by media such as wind or water; they then may cover distances far greater than any that they could have achieved in their amoeboid form, and over regions where amoebae could not travel at all, such as dry surfaces.

References

Zimmer, C. 1998. "The slime alternative." ''Discoverer'', 19(9), 86-93. Mycetozoa Amoeboids {{amoebozoa-stub

See also

References