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Abstract

In a spatially and temporally dynamic environment, animals must forage efficiently in order to thrive. Although foraging is studied extensively in a wide range of species both experimentally and theoretically, the biological substrates of foraging remain poorly understood. To approach a mechanistic understanding of foraging, I used continuous video recordings of \textit{C. elegans} nematodes in patchy landscapes. Comparing quantitative behavioral phenotypes of wild-type animals and mutants, I probed the genetic basis of foraging. Using physiological imaging and optical stimulation of neurons, I also characterized cellular mediation of foraging. In this dissertation, I provide evidence that a key role of serotonergic signaling in \textit{C. elegans} is to accelerate decision-making and promote efficient exploitation of resources in complex environments. My work primarily implicates the serotonergic neuron type NSM, the serotonin-gated chloride channel MOD-1, and the ortholog of mammalian 5-HT1 metabotropic serotonin receptors SER-4 in mediating this process. In addition, I demonstrate how different cells can use a common modulator to affect locomotion in complementary manners. I further show that, like serotonin, TGF-$\beta$ pathway genes contribute to both gradual preemptive slowing as animals approach food and abrupt slowing upon encounter. My observation that double mutants of both \textit{daf-7} and \textit{tph-1} exhibit exaggerated defects relative to single mutants supports the hypothesis that TGF-$\beta$ and serotonin function in parallel rather than in series. Finally, my work implicates both mechanosensory and chemosensory transduction in mediating responses to food encounter, with \textit{daf-7} primarily involved in chemosensation. Taken together, the findings described above demonstrate how multiple signaling pathways play overlapping roles in regulating behavioral responses. Moreover, my work indicates that molecules implicated in mediation of developmental processes can also function on acute timescales to tune behavior.

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