Degree Name

PhD (Doctor of Philosophy)

Program

Biomedical Sciences

Date of Award

8-2018

Committee Chair or Co-Chairs

Thomas C. Jones

Committee Members

Michelle Duffourc, Donald Hoover, Darrell J. Moore, David S. Roane

Abstract

Circadian rhythms are ubiquitous among organisms, influencing a wide array of physiological processes and behaviors including aggression. While many neurophysiological mechanisms are involved in the regulation of aggressive behaviors, relatively few studies have investigated the underlying components involved in the interplay between circadian rhythms and aggression. Spiders are an ideal model system for studying circadian regulation of aggression as they are ecologically both predators and prey. Recent studies have revealed a nocturnal orb- weaving spider Larinioides cornutus exhibits a diel and circadian rhythm in anti-predator behavior (i.e. boldness) that can be manipulated by administration of octopamine (OA) and serotonin (5- HT). Dosing of OA increases boldness of an individual while 5-HT decreases boldness levels. Thus, it appears the serotonergic and octopaminergic system are playing a key role in the daily fluctuations of boldness. This study took a holistic approach to investigate OA and 5-HT levels of head tissue and hemolymph (i.e. blood) as well as the genes involved in synthesis, signaling, and degradation of these monoamines throughout the day (0100, 0700, 1300, and 1900 hours) using HPLC-ED and RNA-sequencing. Although endogenous and circulating levels of OA did not significantly fluctuate, putative transcripts involved in synthesis and signaling did increase in relative expression levels at dusk when L. cornutus begins to actively forage for prey. Endogenous and circulating levels of 5-HT also did not significantly change at the four different time points, but clear patterns of upregulation of 5-HT synthesis enzymes as well as some receptor transcripts were upregulated during the day when L. cornutus would be mostly inactive in its retreat. Lastly, monoamine oxidase, a major catabolic enzyme of monoamines in vertebrates and some invertebrates, was identified in L. cornutus and exhibited substrate specificity for OA compared to 5-HT. Together with the higher enzymatic activity at mid-day compared to dusk, MAO appears to be playing a significant role in regulating the OA and 5-HT signaling in L. cornutus. In conclusion, these results allow a unique preliminary perspective on how OA and 5-HT are influencing the diel shifts in aggression-related behaviors in an ecologically dynamic arthropod.

Document Type

Dissertation - unrestricted

Copyright

Copyright by the authors.

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