like d. discoideum. isn’t it cute? awwwwwww!:
from carl zimmer in the nyt:
“Today, biologists no longer think of Dictyostelium as an embryo: It is more like a society of amoebas that come together for a common cause, for which some will sacrifice themselves.
“The organisms respond to starvation by rushing together by the thousands into a single blob. The blob stretches out into a slug-shaped mass about one millimeter long (one twenty-fifth of an inch), which then crawls like a worm toward light.
“Once it reaches the surface of the soil, the slug undergoes another transformation: Some of the cells turn into a stiff stalk, while the others crawl to the top and form a sticky ball of spores. They stick to the foot of an animal and travel to a hospitable place.
“Inside the slug, about 1 percent of the amoebas turn into police. They crawl through the slug in search of infectious bacteria. When the amoebas find a pathogen, they devour it. These sentinels then drop away from the slug, taking the pathogen with it. They then die of the infection, while the slug remains healthy.
“When the slug is ready to make a stalk, more amoebas must die so that others can live. They climb on top of one another and transform their insides into bundles of cellulose. Twenty percent of Dictyostelium cells die this way, allowing the survivors to climb up their lifeless bodies and become spores.
“David Queller and Joan Strassmann, a husband-and-wife team of Dictyostelium experts at Washington University in St. Louis, have found that some strains of the slime mold are natural-born cheats. If they are mixed with other strains, they are more likely to end up as spores than as dead stalk cells. ‘Clearly this is not just a weird thing,’ Dr. Queller said. ‘Those mutations happen all the time.’
“Research by Dr. Queller and Dr. Strassmann has revealed some reasons the slime-mold world has not been overwhelmed by these cheats. For one thing, most of the amoebas that form a slug are closely related to one another.
“‘They’re helping relatives,’ Dr. Strassmann said. Even if the slime molds die to form a stalk, many of their genes are passed on to the next generation through their kin.
“To help relatives, Dictyostelium needs a way to recognize them. Researchers at Baylor College of Medicine in Houston recently figured out part of the way the slime molds tell kin from strangers. The amoebas make a pair of proteins on the surface of their cells, which fit snugly together — like ‘patches of Velcro,’ as one researcher, Gad Shaulsky, put it.
“Dr. Shaulsky and his colleagues reported in July that if these proteins cannot link to each other, amoebas cannot fuse. ‘They completely ignore each other,’ said Adam Kuspa, another Baylor biologist.”
inclusive fitness — and the behaviors that follow from it — seems to be pretty basic to Life on Earth. i wouldn’t be surprised to learn that dawkins’ pre-genetic replicators also helped out other replicators most like themselves.
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