Hyperoxia avoidance and aggregation behavior in C. elegans

Abstract: Living in the soil, C. elegans can move in three dimensions in search for food. To navigate, it partly uses oxygen levels as a description of its habitat. Oxygen tension may indicate presence of microbial food and location with respect to the surface, where oxygen is 21%. The N2 groups of C. elegans strains differ in their oxygen responses from other strains of this species collected in the wild. This difference is due to a polymorphism in the NPY receptor homologe, NPR-1. The result is two distinct feeding strategies; solitary feeding and feeding in groups (aggregation). NPR-1 antagonizes hyperoxia avoidance on food and N2-like strains, carrying a gain of function mutation in the receptor, feed alone and do not respond strongly to changes in ambient oxygen. In contrast, strains carrying the ancestral form of the receptor, NPR-1 215F, exhibit robust hyperoxia avoidance. These animals aggregate on food, at least in part because animals create a low oxygen environment as they form groups. In paper I we examined how hyperoxia avoidance can trigger aggregation. We showed that when animals encounter a rise in oxygen they initiate a reversal and turn. We showed that similar behaviors direct the animal to stay in an aggregate, and that aggregated animals create a sharp oxygen gradient. We further showed that soluble guanylate cyclases, expressed in the body cavity neurons, and TRPV channels expressed in the nociceptive neurons ASH and ADL, regulate these behaviors. ---text removed from public version--- In paper III we showed that a polymorphic locus, encoding the neuroglobin glb-5, regulates hyperoxia avoidance. The ancestral allele, glb-5(Haw), acts in the body cavity neurons and tunes the dynamic range of these neurons to a narrow range close 21% oxygen. ---text removed from public version--- The data presented in this thesis thus provide novel insights into oxygen sensing in a metazoan, and highlight how oxygen responses promote aggregation behavior of a nematode.