Some species of the nematode worm (Caenorhabditis elegans) are sociable diners, clumping together to share a meal, yet others are more solitary. Why? According to a report by de Bono and Bargmann (Cell 94, 679-689; 1998), these differences can be explained by a change of just one amino acid in a putative neuropeptide receptor.

The authors analysed mutations that cause solitary worm strains to form social aggregates. Solitary worms browse alone on bacterial lawns, forming clumps only when food is scarce. But the mutants always swarm together and show other behavioural differences, such as a tendency to burrow into the agar medium.

All of the mutations that caused worms to turn — from solitary to sociable behaviour — mapped to the gene for NPR-1, a seven-transmembrane-domain receptor. The NPR-1 protein closely resembles neuropeptide-Y receptors, which, in humans, are found throughout the brain. Indeed, de Bono and Bargmann detected C. elegans NPR-1 in neurons of the head, ventral cord and preanal ganglion (pictured).

The authors next studied the npr-1 gene in 15 wild strains of C. elegans. Whereas the solitary worms had a valine residue at position 215 of the NPR-1 chain, their sociable counterparts used phenylalanine. This residue is thought to affect the specificity of NPR-1 signalling through guanine-nucleotide-binding (G) proteins, so it may help to transduce the signals that drive the worms to clump.

Could changes in neuropeptide pathways be a widespread mechanism for altering nematode behaviour? Another study by Nelson et al. (Science 281, 1686-1690; 1998) suggests that they could. These authors disrupted flp-1, a member of the FMRFamide-related neuropeptide gene family in C. elegans, and found behavioural defects in the worms, including a lack of coordination and hyperactivity.

Nematodes probably aggregate because of a mutually attractive stimulus, an as-yet-unknown neuropeptide, that acts through the NPR-1 receptor. Because the worms clump only on bacterial lawns, food is likely to regulate secretion of the neuropeptide — in other words, for worms, as for humans, food is important in social behaviour.