C. elegans discriminates colors to guide foraging

Abstract

A new way to “see” color Color perception is an important aspect of the way many organisms navigate their world. The ability to perceive color has thus far thought to depend on the presence of either eyes or minimally receptive cells containing opsin receptor genes. Ghosh et al. show that foraging Caenorhabditis elegans roundworms, which do not have eyes or opsins, can distinguish a blue color indicative of a toxin released by bacterial mats (see the Perspective by Neal and Vosshall). They suggest that the worms do this through the detection of the ratio between blue and amber light, a process dependent on at least two cellular stress-response genes. Different strains of C. elegans responded to different ratios, suggesting that this pathway plays an ecological role. Science, this issue p. 1059; see also p. 995 Without eyesor opsins, nematodes detect blue pigments associated with bacterial toxins during foraging. Color detection is used by animals of diverse phyla to navigate colorful natural environments and is thought to require evolutionarily conserved opsin photoreceptor genes. We report that Caenorhabditis elegans roundworms can discriminate between colors despite the fact that they lack eyes and opsins. Specifically, we found that white light guides C. elegans foraging decisions away from a blue-pigment toxin secreted by harmful bacteria. These foraging decisions are guided by specific blue-to-amber ratios of light. The color specificity of color-dependent foraging varies notably among wild C. elegans strains, which indicates that color discrimination is ecologically important. We identified two evolutionarily conserved cellular stress response genes required for opsin-independent, color-dependent foraging by C. elegans, and we speculate that cellular stress response pathways can mediate spectral discrimination by photosensitive cells and organisms—even by those lacking opsins.