Student Theses and Dissertations

Date of Award

2019

Document Type

Thesis

Degree Name

Doctor of Philosophy (PhD)

RU Laboratory

Bargmann Laboratory

Abstract

The ability to efficiently locate food is critical for survival. Thus, animals modify their foraging patterns based on recent experience and current conditions to increase their likelihood of finding food. One highly conserved foraging strategy is local search, an intensive exploration over several minutes of the region where food resources were last encountered. As time since the last food encounter passes, animals transition to global search strategies to explore distant areas. The local-to-global search foraging pattern has been observed in fish, reptiles, insects, birds, and mammals, yet few studies ask how an animal’s brain generates this ancient behavior. Here, I ask this question in the nematode Caenorhabditis elegans. In Chapter 1, I characterize the behavior in wildtype animals and find that local search is a food memory that is regulated by food history and by internal satiety states. In addition, I describe the behavior in individual animals and find that although the behavior is reliable at a population level, there is large variability between individuals. In Chapter 2, I conduct a candidate genetic screen to first find a gene important for local search, and then define a circuit for local search behavior. The circuit consists of two parallel multimodal circuit modules that control local search. In each module, chemosensory or mechanosensory glutamatergic neurons that detect food-related cues trigger local search by inhibiting separate integrating neurons through a metabotropic glutamate receptor, MGL-1. The chemosensory and mechanosensory modules are separate and redundant, as glutamate release from either can drive the full behavior. In addition, the ability of the sensory modules to control local search is gated by the internal nutritional state of the animal. In Chapter 3, I characterize neuronal activity within the chemosensory module. Spontaneous activity patterns in the chemosensory module encode information about the time since the last food encounter and correlate with the foraging behavior. Glutamate acts within the module to shape activity patterns at various time scales. Taken together, these experiments reveal a circuit configuration that allows for the robust control of an innate adaptive behavior.

Comments

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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