Student Theses and Dissertations

Date of Award

2016

Document Type

Thesis

Degree Name

Doctor of Philosophy (PhD)

RU Laboratory

Vosshall Laboratory

Abstract

Temperature is a highly dynamic feature of the world, and one that deeply affects living things. Organisms have evolved sophisticated sensory-­motor systems to detect and avoid excessive heat or cold—a behavior termed thermotaxis. In rare cases, however, animals use thermosensation not only to regulate their body temperature, but also to locate food sources in their environment. One example of such an adaptation is found in the female Aedes aegypti mosquito, which becomes attracted to the body heat of endothermic (“warm-­blooded”) hosts when in pursuit of a blood meal. Mosquitoes are remarkably adept at finding hosts in their environment and have become major vectors of human disease, but much remains to be understood about the ethology and sensory neurogenetics of this notorious insect. In this thesis, we used high-­throughput quantitative behavioral assays and genome-­editing techniques to investigate the behavioral rules and molecular basis of mosquito thermotaxis. We have found that female Aedes aegypti are exquisitely sensitive to thermal contrast, and are capable of heat-­seeking in diverse ambient environmental temperatures. By seeking relative warmth and avoiding relative cool, mosquitoes can thermotax towards heated targets. However, mosquitoes also avoid stimuli exceeding the body temperature of their hosts. In this manner, Ae. aegypti are maximally attracted to thermal stimuli approximating endothermic hosts such as humans. We have discovered that the insect thermosensor TRPA1, in addition to playing conserved roles in thermoregulation and chemosensation, is important for thermotactic tuning of heat-­seeking. AaegTRPA1-­/-­ mutant mosquitoes fail to avoid high-­temperature stimuli, and do not distinguish between thermal targets that resemble hosts and those that are inappropriately hot. This AaegTRPA1-­dependent tuning of thermotaxis may be critical for mosquitoes host-­seeking in a complex thermal environment in which hosts are warmer than ambient air, but cooler than surrounding sun-­warmed surfaces. These results demonstrate that evolutionarily conserved thermosensors, conventionally used for maintaining thermoregulatory homeostasis, can be repurposed by blood-­feeding arthropods to help locate and recognize the thermal signatures of their hosts. Our characterization of the behavioral strategies underlying heat-­seeking also helps to establish mosquitoes as a promising model system for the study of thermosensation and thermotaxis. These efforts may inform the design of next-­generation repellents and traps for the control mosquito-­borne diseases.

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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