Chemosensory Attraction of Pfiesteria spp. To Fish Secreta

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Title: Chemosensory Attraction of Pfiesteria spp. To Fish Secreta
Author: Cancellieri, Paul Joseph
Advisors: JoAnn M. Burkholder, Chair
Daniel L. Kamykowski, Member
Nina Stromgren Allen, Member
Abstract: Dinoflagellates represent a diverse group of both auxotrophic and heterotrophic protists. Most heterotrophic dinoflagellates are raptorial feeders that encounter prey using 'temporal-gradient sensing' chemotaxis wherein cells move along a chemical gradient in a directed manner toward the highest concentration. Using short-term 'memory' to determine the orientation of the gradient, dinoflagellates swim in a 'run-and-tumble' pattern, alternating directed swimming with rapid changes in orientation. As the extracellular concentration of the attractant increases, a corresponding increase in the ratio of net-to-gross displacement results in overall movement toward the stimulus.The dinoflagellates Pfiesteria piscicida and P. shumwayae are heterotrophic estuarine species with complex life cycles that include amoeboid, flagellated, and cyst stages, that have been implicated as causative agents in numerous major fish kills in the southeastern United States These organisms show documented 'ambush-predator' behavior toward live fish in culture, including rapid transformations among stages and directed swimming toward fish prey in a manner that suggests the presence of a strong signalling relationship between live fish and cells of Pfiesteria spp.Zoospores of the two species of Pfiesteria can be divided into three functional types: TOX-A designates actively toxic isolates fed on fish prey; TOX-B refers to temporarily non-toxic cultures that have recently (1 week to 6 months) been removed from fish prey (and fed alternative algal prey); and NON-IND refers to isolates without apparent ichthyotoxic ability (tested as unable to kill fish in the standardized fish bioassay process; or without access to fish for ca. 1.5 years). Several Pfiesteria-like dinoflagellates have been isolated from samples in which P. piscicida and P. shumwayae are also present, including several cryptoperidiniopsoid species that have repeatedly been tested as lacking ichthyotoxic capability under ecologically relevant conditions (cell densities that occur in estuaries).Microcapillary assay techniques were employed to determine the attraction of P. piscicida and P. shumwayae zoospores to sterile-filtered fish mucus and excreta. Differences in attraction were measured among functional types, and between these two species and several isolates of cryptoperidiniopsoids, in ten-minute trials in which zoospores entering tubes filled with test substances were observed and counted. TOX-A zoospores of both P. piscicida and P. shumwayae were strongly and comparably attracted to fish secreta/excreta, relative to their behavior toward microcapillary tubes that were filled with filtered seawater. TOX-B zoospores of both Pfiesteria species showed intermediate attraction toward fish materials that appeared to be inversely related to time isolated from fish prey. NON-IND zoospores exhibited low attraction to fish materials. Cryptoperidiniopsoid zoospores showed moderate attraction with no apparent influence of previous exposure to fish.In an additional experiment that examined the signal activity in fish materials over time after collection from fresh fish, unfiltered fish materials ceased to attract P. piscicida zoospores after approximately 48 hours and ultrafiltered materials maintained attractive ability over the duration of the experiment (72 hours). These data show that filtration of fish materials may be used to extend the useful life of the chemical signal, possibly by removing bacteria that consume or degrade it.In recent years, several researchers have identified fish kairomones (pheromones that benefit the recipient) present in fish mucus that induce life history and behavioral changes in a range of zooplankters. It is likely that one or more of these kairomones, or similar compounds, are responsible for the behavioral and developmental changes observed in Pfiesteria spp. in the presence of live fish. Data from these experiments support the current understanding that significant behavioral differences exist between functional types of Pfiesteria spp., and between these toxic dinoflagellate species and known lookalike dinoflagellates without ichthyotoxic activity under ecologically relevant conditions.
Date: 2001-04-04
Degree: MS
Discipline: Botany

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