The Evolutionary Construction of Sleep

Citation

Nath, Ravi David (2018) The Evolutionary Construction of Sleep. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/JPDW-JW81. https://resolver.caltech.edu/CaltechTHESIS:05272018-025533397

Abstract

To understand the biological basis of sleep we need to understand its neuronal and genetic regulation. In this thesis, I explore how individual behaviors serve as building blocks to construct the sleep state where a block is defined as a set of measurable behaviors. These behavioral blocks are shaped by evolutionary forces. From one animal to the next, blocks may remain or change. If a block remains across all the sleep states in the metazoan lineage then it must have an important and conserved role in sleep regulation. For example, reduced locomotion is a behavior that is often observed during sleep. There are two possible explanations for the changing of a block: either the block was vestigial or the block was easily replaceable with another block that fulfills the same function. Consider sleep duration: some animals may require five hours of sleep, while others only require one hour. The changing of a block is one way that the sleep state could evolve. Blocks may also be added during the evolution of the sleep state, increasing the dimensions and number of tasks that are accomplished during sleep. Here, I discuss the origin of sleep, as well as its conserved neuronal and genetic regulation. I report the following: the discovery of sleep in jellyfish which are among the first animals to evolve neurons and the identification of novel sleep regulators in the roundworm Nematode Caenorhabiditis elegans (C. elegans). The sleep regulators discovered in C. elegans may have conserved functions in vertebrates. These studies show that some sleep behaviors and various sleep molecules change or remain homologous across metazoans. The studies are united by our simple block hypothesis of sleep construction.

Thesis Files