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September 09, 2013

Adopted sub-species of bees become genetically like their adopting colony and there are human implications for genetic changes from social isolation for the elderly

A scientist has tested the genetic effect of swapping baby sweet tempered European honeybees with aggressive African killer bees. (H/T Chris Phoenix)

They took 250 of the youngest bees from each hive, and painted marks on the bees’ tiny backs. Then they switched each set of newborns into the hive of the other subspecies.

He didn’t expect the bees’ actual DNA to change: Random mutations aside, genes generally don’t change during an organism’s lifetime. Rather, he suspected the bees’ genes would behave differently in their new homes—wildly differently.

This notion was both reasonable and radical. Scientists have known for decades that genes can vary their level of activity, as if controlled by dimmer switches. Most cells in your body contain every one of your 22,000 or so genes. But in any given cell at any given time, only a tiny percentage of those genes is active, sending out chemical messages that affect the activity of the cell. This variable gene activity, called gene expression, is how your body does most of its work.

Where he went out on a limb was in questioning the conventional wisdom that environment usually causes fairly limited changes in gene expression. It might sharply alter the activity of some genes, as happens in cancer or digestion. But in all but a few special cases, the thinking went, environment generally brightens or dims the activity of only a few genes at a time.



When Alaux looked at the gene-expression profiles of the bees exposed again and again to alarm pheromone, he and Robinson saw why: With repeated alarms, hundreds of genes—genes that previous studies had associated with aggression—grew progressively busier. The rise in gene expression neatly matched the rise in the aggressiveness of the bees’ response to threats.

Robinson had not expected that. “The pheromone just lit up the gene expression, and it kept leaving it higher.” The reason soon became apparent: Some of the genes affected were transcription factors—genes that regulate other genes. This created a cascading gene-expression response, with scores of genes responding.

This finding inspired Robinson’s kidnapping-and-cross-fostering study. Would moving baby bees to wildly different social environments reshape the curves of their gene-expression responses? Down in Ixtapan, Robinson’s collaborators suited up every five to 10 days, opened the hives, found about a dozen foster bees in each one, and sucked them up with a special vacuum. The vacuum shot them into a chamber chilled with liquid nitrogen. The intense cold instantly froze the bees’ every cell, preserving the state of their gene activity at that moment. At the end of six weeks, when the researchers had collected about 250 bees representing every stage of bee life, the team packed up the frozen bees and shipped them to Illinois.

Robinson’s staff removed the bees’ sesame-seed-size brains, ground them up, and ran them through a DNA microarray machine. This identified which genes were busy in a bee’s brain at the moment it met the bee-vac. When Robinson sorted his data by group—European bees raised in African hives, for instance, or African bees raised normally among their African kin—he could see how each group’s genes reacted to their lives.

Robinson organized the data for each group onto a grid of red and green color-coded squares: Each square represented a different gene, and its color represented the group’s average rate of gene expression. Red squares represented genes that were especially active in most of the bees in that group; the brighter the red, the more bees in which that gene had been busy. Green squares represented genes that were silent or underactive in most of the group. The printout of each group’s results looked like a sort of cubist Christmas card.

When he got the cards, says Robinson, “the results were stunning.” For the bees that had been kidnapped, life in a new home had indeed altered the activity of “whole sectors” of genes. When their gene expression data was viewed on the cards alongside the data for groups of bees raised among their own kin, a mere glance showed the dramatic change. Hundreds of genes had flipped colors. The move between hives didn’t just make the bees act differently. It made their genes work differently, and on a broad scale.

What’s more, the cards for the adopted bees of both species came to ever more resemble, as they moved through life, the cards of the bees they moved in with. With every passing day their genes acted more like those of their new hive mates (and less like those of their genetic siblings back home). Many of the genes that switched on or off are known to affect behavior; several are associated with aggression. The bees also acted differently. Their dispositions changed to match that of their hive mates. It seemed the genome, without changing its code, could transform an animal into something very like a different subspecies.

These bees didn’t just act like different bees. They’d pretty much become different bees. To Robinson, this spoke of a genome far more fluid—far more socially fluid—than previously conceived.

Human Implications of Stress and Isolation

“We typically think of stress as being a risk factor for disease,” said Cole. “And it is, somewhat. But if you actually measure stress, using our best available instruments, it can’t hold a candle to social isolation. Social isolation is the best-established, most robust social or psychological risk factor for disease out there. Nothing can compete.”

This surely has implications for gerontology, given how isolated a lot of our elders are in the US

Of roughly 22,000 genes in the human genome, the lonely and not-lonely groups showed sharply different gene-expression responses in 209. That meant that about one percent of the genome—a considerable portion—was responding differently depending on whether a person felt alone or connected.

Cole often puts it differently at the end of his talks about this line of work. “Your experiences today will influence the molecular composition of your body for the next two to three months,” he tells his audience, “or, perhaps, for the rest of your life. Plan your day accordingly.”


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