Selfish genes hide for decades in plain sight of worm geneticists

By poisoning offspring and providing the antidote, the genes spread spookily fast through the population

C. elegans nematode
MOMMIE DEAREST Covertly poisoning offspring appears to be a common part of motherhood in the C. elegans nematode (shown) that stars in biology labs worldwide.

A strain of wild Hawaiian worms has helped unmask long-studied genes as just plain selfish. The scammers beat the usual odds of inheritance and spread extra fast by making mother worms poison some of their offspring.

Biologists have for decades discussed how two genes in the familiar lab nematode Caenorhabditis elegans might help embryos build their organs. Working with a little-studied wild strain, however, caused a rethink of the genes’ supposedly beneficial role “that flipped it on its head,” says UCLA geneticist Leonid Kruglyak.

Instead of doing some body sculpting, the gene sup-35 doses the eggs with a toxin that will kill them after fertilization, two postdocs in the Kruglyak lab discovered. The toxin gene doesn’t poison itself out of the gene pool because it’s linked to a partner, pha-1, that lets embryos manufacture an antidote. Embryos die unless they inherit a copy of the antidote gene in either egg or sperm, and so the poison-antidote duo can spread unusually fast through populations.

Making a mom on occasion poison some of her offspring doesn’t benefit her but certainly helps the genes. Thus the long-known sup-35 and pha-1 form what’s called a selfish genetic element, Kruglyak’s team proposes May 11 in Science.

That analysis is “very clearly accurate,” says evolutionary geneticist Jack Werren of the University of Rochester in New York. The idea that a gene could behave selfishly, promoting its own spread regardless of its host’s interests, was once controversial (SN: 3/19/16, p. 12). But as molecular biology techniques have improved, researchers have found more and more examples. Many of the most dramatic forms of selfishness, the murderous cheats, come from bacteria, so Werren welcomes the C. elegans scam as a rare case discovered in animals.

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Toxic effects

Getting a poison from mom doesn’t matter if she also passes along a gene for the antidote. That’s…