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.