Student Theses and Dissertations


Joshua Greene

Date of Award


Document Type


Degree Name

Doctor of Philosophy (PhD)

RU Laboratory

Bargmann Laboratory


Game theory has long predicted that the density of competitors and their behaviors should affect foraging, and moreover suggests that multiple strategies can evolve and co-exist within a single species. I show that both of these predictions are met by foraging Caenorhabditis elegans. In Chapter 2, I show that animals alter their foraging behavior in response to population density, that certain pheromones induce this behavioral change, and that different wild isolates vary in response to the potent ascaroside icas#9. I use QTL mapping to find a major locus responsible for this variation, and map it to an icas#9 receptor, srx-43. Reduced expression of this gene in the sensory neuron ASI contributes to naturally occurring insensitivity to icas#9. Remarkably, I find that the QTL falls in a high-diversity region that exists in two distinct haplotypes in C. elegans populations around the world. This pattern of diversity is consistent with a locus under balancing selection, and through competition experiments, I show that indeed the two haplotypes result in differential fitness depending on icas#9 and food distribution. In Chapter 3, I extend these findings by showing that a second chemoreceptor, srx-44, is also a component of the initial QTL. A gain-in-function in srx-44 contributes to reduced icas#9 sensitivity in the wild isolates that have reduced expression of srx-43. Through the use of transgenic animals and CRISPR/Cas9-mediated mutagenesis, I identify a polymorphism in the promoter of this gene causing increased expression in the sensory neuron ASJ, in which srx-44 acts to suppress icas#9 response. In Chapter 4, I examine pheromone regulation of foraging behavior in animals lacking specific neurotransmitters or neurotransmitter receptors. This screen identified GABA as broadly necessary for ascaroside-suppression of roaming. Through cell specific rescue and inhibition experiments, I show that GABA release from the unpaired AVL neuron is both necessary and sufficient for this behavior. Taken together, these experiments provide insight into the genetics and neural circuitry underlying social communication and foraging behavior.


A Thesis Presented to the Faculty of The Rockefeller University in Partial Fulfillment of the Requirements for the degree of Doctor of Philosophy

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