Cannibal worms recognize their children—and don’t eat them as a result

Bigger than a poppy seed but smaller than a sesame seed—and about as featureless to the human eye—nematodes are nevertheless very good at telling their relatives apart. They’re so good, in fact, that the cannibals among them chow down on any other nematode in sight, except their own young. Now, researchers say they know why.

Scientists started by examining the nematode Pristionchus pacificus, a worm that often lives on scarab beetles. Some survive on just bacteria, but some are predators that consume other nematodes, even those of the same species. But the researchers were puzzled by the fact that even the cannibal worms never ate their own kin.

So, the scientists compared the genomes of their lab nematode and another nematode species to see whether any genes might aid in this so-called self-recognition. When they modified P. pacificus worms using the gene-editing technique CRISPR, they discovered a gene they call SELF-1 was responsible for kin protection. When the DNA of SELF-1 was changed, the offspring were consumed, they report today in Science.

The researchers further discovered that one part of the SELF-1 gene varies quite a bit between nematodes, leading to slightly different molecules in the skin of even closely related individuals. The researchers hope to learn what molecular mechanism causes the self-recognition gene to vary so much and what other molecules are involved in telling kin from nonkin—something that might eventually help us understand self-recognition in other species.