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The Problem Pacific lamprey (Lampetra tridentata) populations are in decline or have been extirpated from much of their historical range in the Columbia River Basin. A variety of factors related to human development of the region, including hydropower operations, municipal waste discharge, and habitat degradation, may be responsible for these declines. Tribal, state, and federal agencies have joined together to learn more about lampreys in the Columbia River Basin with the explicit goal of rehabilitating the populations. A pilot study of Pacific lamprey rehabilitation is underway in the Umatilla River Basin of Oregon. Evaluation of the rehabilitation effort is a complex process requiring knowledge of the life history and behavior of Pacific lampreys. Since little is known about Pacific lampreys, research on another species of anadromous lamprey, the sea lamprey (Petromyzon marinus), has been considered a starting point. Evidence collected for sea lampreys suggests they may not home to natal streams, but instead may use their olfactory ability to detect the presence of larval and adult lampreys as discrete migratory cues.
Applying these same concepts to the study of Pacific lampreys, the USGS has designed experiments to determine the role of pheromones in the upstream migration of Pacific lampreys. Knowledge of the affects of pheromones on the behavior of Pacific lampreys could aid in the rehabilitation of this species. Using both physiological and behavioral methods, we will examine the relative sensitivity of upstream migrating Pacific lampreys to lamprey bile acids and other compounds during the freshwater phase of their maturation. Objectives The proposed olfactory study of Pacific lampreys has three phases. The first, completed in 2000, was to construct and test an electro-olfactogram (EOG) apparatus capable of measuring olfactory responses of Pacific lampreys to specific odorants. The second phase, begun in 2001 and continuing through 2003, uses EOG to measure temporal variation in olfactory responses of migrating Pacific lampreys to potential pheromones produced by larval and sexually mature lampreys. Specifically, this phase will determine which compounds emitted by larvae and adults are potential attractants, and describe the timing of changes in pheromone sensitivity in adults, thereby identifying which compounds may be attractants at key points during migration and spawning. The third phase, begun in 2002 and continuing through 2004, will assay behavioral responses of upstream migrating Pacific lampreys to pheromones identified in Phase 2 as potential attractants. Although EOG studies can reveal which compounds are strong olfactory stimulants, they cannot reveal what their effects may be on the migratory behavior of Pacific lampreys. Assays of behavioral responses to potential pheromones identified in Phase 2 will clarify the biological significance of olfactory responses to these pheromones during migration and spawning. Methodology
Upstream migrating Pacific lampreys were collected from the wild and held at the Columbia River Research Laboratory in Cook, WA through spawning the following spring. Olfactory responses of captive adult Pacific lampreys were measured by recording electro-olfactograms (EOGs) at intervals from the time of capture through spawning. Once a satisfactory standard response and baseline were established, the olfactory organ was exposed to a series of concentrations of each test odorant and the results were recorded. Stock solutions of standard and test odorants were prepared prior to experiments, and dilutions of these stocks were prepared on the day of the experiment. A 10-2 M L-arginine stock was prepared biweekly in deionized water and stored at 4°C for a maximum of two weeks. Bile acid stocks were prepared in methanol as needed at a concentration of 10-3 M. Petromyzonol sulfate, 3-keto petromyzonol sulfate, and taurolithocholic acid 3-sulfate were stored at -80°C, and allocholic acid was stored at -20°C. A 3-minute interval of blank water between odorant administrations was employed to allow the olfactory receptors to recover. Exposures to the L-arginine standard were performed every 30 minutes to 1 hour. A methanol blank was periodically employed as well. Each odorant exposure was replicated twice to ensure repeatability of measurements. Peak heights of olfactory responses were measured and expressed as a percent of standard responses. Duplicate responses for each test odorant were averaged and expressed as a percent of the average of standard responses performed before and after the test odorant. Expression of EOG responses as a percentage of the standard response controlled for inter-experimental differences in electrode placement and individuals tested. Plots of dose-response curves were made for each test interval and changes in olfactory responsiveness of Pacific lampreys over time were described. Highlights and Key Findings During 2001 and 2002, we examined the olfactory response of adult Pacific lampreys to larval lamprey bile acids, petromyzonol sulfate (PS), allocholic acid (ACA), and an adult male sea lamprey pheromone (3-keto PS). Similar to sea lampreys, upstream migrating Pacific lampreys responded to PS and 3-keto PS with large negative potential EOGs. However, unlike sea lampreys, Pacific lampreys have shown few measurable olfactory responses to ACA. Additionally, the responses to PS and 3-keto PS were smaller than those reported for the sea lamprey. Where Are We Headed In 2003
In 2003, we will continue to measure the temporal variation in the olfactory response of upstream migrating Pacific lampreys to pheromones produced by larval and sexually mature lampreys using EOG techniques. We will also assay behavioral responses of upstream migrating Pacific lampreys to pheromones produced by larval and sexually mature lampreys. The current study of olfaction in Pacific lampreys will support the research and restoration efforts of the Confederated Tribes of the Umatilla Indian Reservation and will provide information for the management of this species in the Columbia River Basin. Specifically, the purpose of this study is to investigate the role of pheromones in the migration and spawning behaviors of Pacific lampreys. Knowledge of the role of pheromonal cues in the life history of Pacific lampreys will enable managers to determine factors that may be limiting the success of this species in the Columbia River Basin. Project Contact Jennifer Bayer Email: jennifer_bayer@usgs.gov Publications |
