To optimize foraging in natural environments, animals continuously make complex decisions about the suitability of their surroundings. These decisions require simultaneously processing sensory information, usually of different types (e.g., visual, auditory, etc.) about the environment, as well as an assessment of internal physiological state. How animals make these decisions is incompletely understood. I used the nematode worm Caenorhabditis elegans in two distinct contexts to investigate how multisensory integration contributes to foraging decisions.
Like any animal, while foraging C. elegans must approach and obtain food while avoiding various threats, which for them include toxic chemicals and hyperosmotic concentrations of otherwise innocuous solutes. Little is known, however, in any animal about cellular and molecular mechanisms underlying decisions balancing avoidance of danger with approach to things of value. I confronted worms with a decision whether to cross a hyperosmotic barrier, presenting the threat of desiccation, to reach a source of food odor. I found that activation of a neuropeptide receptor in the higher-order "RIM" interneuron biases the worm against crossing the barrier. Unexpectedly, however, RIM controls this decision not by synaptic signaling to downstream motor command circuits, but rather by top-down extrasynaptic aminergic signaling directly onto the primary osmosensory neuron to tune its sensitivity to the barrier. Furthermore, I found that food deprivation increases the worm's willingness to cross the dangerous barrier by suppressing this pathway. Overall this work reveals a potentially general neural circuit basis for internal state control of threat-reward decision making.
Using another behavioral paradigm, I have found that contrary to expectations, worms possess a color discrimination system that guides their foraging decisions despite lacking any opsin or other photoreceptor genes. C. elegans live in decomposing organic matter where they feed on microorganisms, some of which secrete colorful pigments. However, it was unknown whether worms use light information, potentially including color, to inform foraging behaviors in environments containing colorful food sources. Interestingly, I found that simulated daylight guides C. elegans foraging decisions with respect to harmful bacteria that secrete a blue pigment toxin. By absorbing yellow-orange light, this blue pigment toxin alters the color of light sensed by the worm, and thereby triggers an increase in avoidance of harmful bacteria. Not only does this work reveal an unexpected contribution of visual stimuli to worm behavioral ecology, it also establishes the existence of a color detection system that is distinct from those of other animals.
|School Location:||United States -- Connecticut|
|Source:||DAI-B 78/11(E), Dissertation Abstracts International|
|Keywords:||Behavior, C.Elegans, Decision, Multisensory, Neuroscience|
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