Student Theses and Dissertations


Elias Scheer

Date of Award


Document Type


Degree Name

Doctor of Philosophy (PhD)

RU Laboratory

Bargmann Laboratory


Foraging animals dynamically adjust their behavioral patterns over time to optimize feeding in their environment. In the nematode Caenorhabditis. elegans, foraging animals alternate between states of locomotory arousal. I observed that animals in low activity states remain nearby food patches, whereas highly aroused animals often exit patches to explore the external environment. Using different methods of behavioral state classification reveals different aspects of foraging behavior: previously described high arousal roaming and low arousal dwelling states reflect long-term changes in locomotory patterns, whereas an Autoregressive Hidden Markov model that classifies behavior on shorter time scales effectively segments food leaving behaviors. Adaptive foraging strategies rely on animals’ ability to integrate internally sensed physiological needs and external sensory cues with ongoing internal state. Consistent with this, I find that animals acutely unable to eat food drastically increase high arousal behavioral states and food leaving behavior, motivated by internal sensing of the absence of food. I also find that mutants lacking sensory transduction or neuromodulatory signaling each show dysregulated behavioral states surrounding food leaving behavior. In C. elegans, animals spontaneously alternate between roaming and dwelling states in environments that contain a uniform food density. However, I find that animals encountering environments with non-uniform food distributions entrain their behavioral state transitions to locally experienced changes in food density. Experience of dwindling food resources over several minutes triggers increased locomotion speed and stimulates roaming behavior, whereas entry into denser food patches suppresses speed and causes animals to dwell. In mutants with deficient chemosensory transduction, this sensory entrainment is lost. I also find that animals lacking a functional PDF receptor (PDFR-1) show both reduced roaming and attenuated sensory coupling of locomotory behavior. Restoring pdfr-1 expression in interneurons stimulates roaming but fails to rescue sensory coupling, suggesting that other sites of pdfr-1 expression may drive this. I conclude that internal states integrate sensory stimuli and physiological needs to facilitate effective foraging strategies on both short and long time scales.


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

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