Wild Strains Reveal Natural Variation in C. elegans Avoidance Behaviors

Chemical stimuli, including odorants and tastants, provide information about food availability and allow animals to avoid harmful environments. Over six decades of research using primarily one laboratory-adapted strain of the nematode Caenorhabditis elegans has yielded a wealth of information about how this animal senses and responds to chemical cues to survive. However, it was not known whether the chemosensory behavioral profile of this strain (named N2) is representative of the species. Using a collection of hundreds of wild C. elegans strains collected from around the globe, we assessed their abilities to respond to three aversive stimuli (the bitter tastant quinine, the heavy metal copper, and the detergent SDS) in a laboratory setting and found ∼10-20 fold differences in response sensitivities among the strains. Further, response sensitivities to one stimulus were largely uncoupled from responses to the other stimuli and uncorrelated with the geographical locations from which the wild strains were collected. Using genome-wide association studies, we identified unique regions significantly correlated with different responses to each stimulus. Near-isogenic lines were created to confirm the effects of two genomic regions on differential avoidance behavior to the bitter tastant quinine. Combined, we report remarkable natural variation in chemosensory behavioral responses among wild C. elegans strains and describe two new quantitative trait loci associated with decreased response sensitivity to quinine.