slime mold decisions: begins to study loners (Introduction)

by David Turell @, Thursday, May 21, 2020, 20:42 (11 days ago) @ David Turell

Not everyone cooperates in stalk building. Why?:

"Yet there are always individuals that don’t participate in the collective behavior — the odd bird or insect or mammal that remains just a little out of sync with the rest; the stray cell or bacterium that seems to have missed some call to arms. Researchers usually pay them little heed, dismissing them as insignificant outliers.

"But a handful of scientists have started to suspect otherwise. Their hunch is that these individuals are signs of something deeper, a broader evolutionary strategy at work. Now, new research validating that hypothesis has opened up a very different way of thinking about the study of collective behavior.


"Scientists have used slime molds to experimentally investigate the emergence and maintenance of social behavior, identifying mechanisms that ensure cooperation among the amoebas. But they’ve always focused on the aggregated cells. Tarnita and her team wanted to investigate whether the cells that stayed behind — the “loners,” as they called them — also played an important role.

"As they reported in 2015, those loners turned out to be perfectly functional, eating and dividing regularly in the presence of nutrients. Their offspring could aggregate normally when starved — and they always left behind some loners of their own. Their presence seemed to be a consistent aspect of slime mold behavior.


"One shock was that the loners constituted up to 30% of the original population, sometimes exceeding the number of cells in the aggregate’s stalk.

But that wasn’t all. The researchers had predicted that a constant fraction of cells would stay behind in each test. That would have meant that each cell was in effect independently flipping a (weighted) coin about whether to participate in the collective behavior. “We totally thought it was going to be a coin flip,” Rossine said. “We were convinced.”

"As the scientists reported in March in PLOS Biology, however, instead of a constant fraction of loners, they found a constant number of them. “There is some sort of a set point that the cells have memorized,”


"That natural variation between strains means that loner behavior is a heritable trait that natural selection can act on. Further experiments and simulations showed that this number is also influenced by environmental factors, which affect how the cells’ chemical signals diffuse and interact to facilitate — or impede — aggregation.


"The loner cells might therefore serve as a form of insurance in case any of those [adverse] situations transpire. By staying out of the group, “you leave behind these seeds,” Tarnita said — seeds that could regenerate the population and its multicellular dynamics all on their own.


" (1) The researchers hope to pin down what’s happening at the molecular level to enable this strategy in the slime molds. But they’re most excited by the prospect of studying loners in other systems. “The theoretical idea of the loner as something that stabilizes the existence of the group is a very powerful one,” Rossine said. (my bold)


"There are other contexts in which loner behavior might prove evolutionarily crucial as well. Couzin and others have found, for instance, that some forms of loner behavior can lead to the emergence of leaders in groups. (2)“Are these differences predetermined?” Couzin said. Or are they products of “a decision-making strategy that depends on both the physical and the biotic environment around the animals?”


"the work demonstrates that to truly understand how collective and cooperative behaviors evolved, and how they continue to operate, researchers may need to study the seeming misfits that don’t participate."

Comment: dhw should delight in this study. It is not about cooperating multicellular cells. They are built that way in the process of embryological development. This is about individual cells who make decisions. Note the first bold. It could be automatic molecular reactions which are due to (see bold 2) environmental factors. However, slime mold is a step on the way to multicellularity. Does that mean some cells in the huge multicellular group can actually be independent and act intellectually? We don't know what tells DNA to add methyl groups in epigenetics! There is a reason for that: We can read genes in the code, and we can show what the gene does, but we have no idea how that gene does it!!! Also, what signals DNA to make modifications? These disconnects in what we can understand may never be solved. But they are the key to speciation. The hemoglobin article from yesterday says two mutations did it. Not by chance. An easy dabble for God to insert the changes.

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