Modulation of the sea lamprey (Petromyzon marinus) pheromone communication system may offer additional effective and environmentally benign approaches to manage populations in the Laurentian Great Lakes where they are invasive predators of large fishes. Previous studies showed that pheromones are indispensable cues that mediate sea lamprey migration and reproduction. Mature male sea lampreys release a multi-component sex pheromone that contains 3-keto petromyzonol sulfate (3kPZS) as a main component. 3kPZS is a potent odorant that induces upstream movement of ovulated females to the spawning grounds with nesting mature males. While the function and potential management implications of 3kPZS are well-studied, the identity of other putative sex pheromone components and the utility of pheromone antagonists that disrupt the sea lamprey pheromone communication system remain largely unknown. In this dissertation, I characterize novel pheromone components released by mature male sea lampreys and identify antagonists that disrupt the olfactory and behavioral responses to the sea lamprey sex pheromone components. In Chapter 1, I provide evidence that spermine is a sex pheromone released by mature male sea lampreys through the emission of milt (fish semen). Spermine is detected by two trace amine-associated receptors expressed in the olfactory epithelium, induces olfactory responses at a sub-femtomolar concentration, and attracts ovulated females but not mature males. These results reveal a new source and chemical template of sea lamprey pheromones in addition to identifying a secondary benefit of male gamete release; that is to recruit additional mates in sea lampreys. In Chapter 2, I provide evidence that PZS treatment interferes with the responses to 3kPZS. Electro-olfactogram recordings from sea lampreys indicate PZS reduces the olfactory response to 3kPZS in a concentration-dependent manner. Behavioral results from maze assays and field experiments in-stream indicate the PZS disrupts 3kPZS-mediated behavioral responses in ovulated females as well. In Chapter 3, I provide evidence that petromyzonol-3,7,12,24-tetrasulfate (3sPZS), which was identified as a candidate 3kPZS antagonist through virtual screening in a previous study, selectively reduces the 3kPZS olfactory response. 3sPZS also reduces the behavioral preference of ovulated females for 3kPZS in the maze and reduces upstream movement, entry, and retention in artificial nest baited with 3kPZS in a natural spawning environment. The collective results of electrophysiology through field trials in a natural spawning environment provide a proof of concept that pheromone antagonists may be useful to disrupt vertebrate pheromone communication. In Chapter 4, I describe the methodology of bioassay-guided fractionation as an effective and interdisciplinary approach to isolate and characterize the structure, olfactory potency, and behavioral response of putative pheromones of sea lampreys. In Appendices A−C, I report the structures, olfactory potencies, and female behavioral preferences of eight novel bile salts or bile alcohols released from mature male sea lampreys. The results further elucidate the identity and bioactivity of the multi-component sex pheromone released by mature male sea lampreys. In addition, the identified naturally occurring and synthetic pheromone antagonists may offer new control tactics to manipulate behavioral responses or disrupt mating of sea lampreys. Taken together, the results on sea lamprey pheromones and pheromone antagonists can help guide an effective, integrated sea lamprey control program in the Laurentian Great Lakes.
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