Within the last two decades, Prymnesium parvum (golden algae) has rapidly spread into inland wate... more Within the last two decades, Prymnesium parvum (golden algae) has rapidly spread into inland waterways across the southern portion of North America and this organism has now appeared in more northerly distributed watersheds. In its wake, golden algae blooms have left an alarming trail of ecological devastation, namely massive fish kills, which are threatening the economic and recreational value of freshwater systems throughout the United States. To further understand the nature of this emerging crisis, our group investigated the chemical nature of the toxin(s) produced by P. parvum. We approached the problem using a two-pronged strategy that included analyzing both laboratory-grown golden algae and field-collected samples of P. parvum. Our results demonstrate that there is a striking difference in the toxin profiles for these two systems. An assemblage of potently ichthyotoxic fatty acids consisting primarily of stearidonic acid was identified in P. parvum cultures. While the concentration of the fatty acids alone was sufficient to account for the rapid-onset ichthyotoxic properties of cultured P. parvum, we also detected a second type of highly labile ichthyotoxic substance(s) in laboratory-grown golden algae that remains uncharacterized. In contrast, the amounts of stearidonic acid and its related congeners present in samples from recent bloom and fish kill sites fell well below the limits necessary to induce acute toxicity in fish. However, a highly labile ichthyotoxic substance, which is similar to the one found in laboratory-grown P. parvum cultures, was also detected. We propose that the uncharacterized labile metabolite produced by P. parvum is responsible for golden algae's devastating fish killing effects. Moreover, we have determined that the biologically-relevant ichthyotoxins produced by P. parvum are not the prymnesins as is widely believed. Our results suggest that further intensive efforts will be required to chemically define P. parvum's ichthyotoxins under natural bloom conditions.
Background/Question/Methods All invasive species must successfully invade and establish before th... more Background/Question/Methods All invasive species must successfully invade and establish before they can spread. Early detection is key to limiting the spread of invasives, but can be particularly difficult for invasive microbes. The microbiologist's credo 'Everything is everywhere, but, the environment selects,' infers that microbial invasions are relatively continuous with success of population establishment dependent on environmental conditions. Therefore, environmental factors should be instrumental in predicting invasion success and establishment for microbial invaders. Prymnesium parvum, a toxigenic marine unicellular eukaryote, has invaded many freshwater systems throughout the southern and southwestern US. Like many invading species it can potentially wreak havoc in the invaded system, in this case, leading to massive fish kills during blooms. We've been monitoring P. parvum abundances in Lake Texoma (OK-TX) since the 2004 invasion and recently adopted qPCR as...
The growth rate hypothesis (GRH) proposes that variation in organismal C : N : P ratios is associ... more The growth rate hypothesis (GRH) proposes that variation in organismal C : N : P ratios is associated with growth rate due to differential allocation to P-rich ribosomal RNA to support growth. A further extension of the GRH proposes that this variation is associated with the structure of ribosomal (r)DNA genes (e.g., promoter-enhancer sequences in the rDNA intergenic spacer [IGS]) that influence the production rate of rRNA. To test these ideas, we examined growth rate, rDNA structure, RNA : DNA ratios, and elemental composition (C : N : P) in multiple clones of three Daphnia species (pulex, pulicaria, magna) in controlled laboratory experiments. Results show that a portion of the rDNA motif, consisting primarily of the IGS, shows considerable interspecific and intraspecific length variation. Significant interspecific differences in all parameters were found, while significant intraspecific (clone) effects were detected only for RNA : DNA ratios and growth rate. As predicted by the GRH, there were significant positive correlations between RNA : DNA ratio and either growth rate or rDNA/IGS length, and a significant positive correlation between rDNA/IGS length and growth rate, when clonal means for all three species were examined. However, no clear-cut relationships between RNA : DNA and either C : P or N : P were observed for any of the three species. Likewise, no discernible intraspecific relationships between growth rate and either C : P or N : P were detected. These preliminary findings suggest that further study of elemental composition, nucleic acid content, and growth rates of organisms may lead to a clearer understanding of the role of stoichiometric constraints in influencing the ecology and evolution of natural populations.
The role of stoichiometric food quality in influencing genotype coexistence and competitive inter... more The role of stoichiometric food quality in influencing genotype coexistence and competitive interactions between clones of the freshwater microcrustacean, Daphnia pulex, was examined in controlled laboratory microcosm experiments. Two genetically distinct clones of D. pulex, which show variation in their ribosomal (r)DNA structure, as well as differences in a number of previously characterized growth-rate-related features (i.e., life-history features), were allowed to compete in two different arenas: (1) batch cultures differing in algal food quality (i.e., high vs. low carbon:phosphorus (C:P ratio) in the green alga, Scenedesmus acutus); (2) continuous flow microcosms receiving different light levels (i.e., photosynthetically active radiation) that affected algal C:P ratios. In experiment 1, a clear genotype · environment interaction was determined with clone 1 out-competing clone 2 under high nutrient (i.e., low food C:P) conditions, while the exact opposite pattern was observed under low nutrient (i.e., high C:P) conditions. In experiment 2, clone 1 dominated over clone 2 under high light (higher C:P) conditions, but clonal coexistence was observed under low light (low C:P) conditions. These results indicate that food (nutrient) quality effects (hitherto an often overlooked factor) may play a role in microevolutionary (genotypic) responses to changing stoichiometric conditions in natural populations.
Within the last two decades, Prymnesium parvum (golden algae) has rapidly spread into inland wate... more Within the last two decades, Prymnesium parvum (golden algae) has rapidly spread into inland waterways across the southern portion of North America and this organism has now appeared in more northerly distributed watersheds. In its wake, golden algae blooms have left an alarming trail of ecological devastation, namely massive fish kills, which are threatening the economic and recreational value of freshwater systems throughout the United States. To further understand the nature of this emerging crisis, our group investigated the chemical nature of the toxin(s) produced by P. parvum. We approached the problem using a two-pronged strategy that included analyzing both laboratory-grown golden algae and field-collected samples of P. parvum. Our results demonstrate that there is a striking difference in the toxin profiles for these two systems. An assemblage of potently ichthyotoxic fatty acids consisting primarily of stearidonic acid was identified in P. parvum cultures. While the concentration of the fatty acids alone was sufficient to account for the rapid-onset ichthyotoxic properties of cultured P. parvum, we also detected a second type of highly labile ichthyotoxic substance(s) in laboratory-grown golden algae that remains uncharacterized. In contrast, the amounts of stearidonic acid and its related congeners present in samples from recent bloom and fish kill sites fell well below the limits necessary to induce acute toxicity in fish. However, a highly labile ichthyotoxic substance, which is similar to the one found in laboratory-grown P. parvum cultures, was also detected. We propose that the uncharacterized labile metabolite produced by P. parvum is responsible for golden algae's devastating fish killing effects. Moreover, we have determined that the biologically-relevant ichthyotoxins produced by P. parvum are not the prymnesins as is widely believed. Our results suggest that further intensive efforts will be required to chemically define P. parvum's ichthyotoxins under natural bloom conditions.
Background/Question/Methods All invasive species must successfully invade and establish before th... more Background/Question/Methods All invasive species must successfully invade and establish before they can spread. Early detection is key to limiting the spread of invasives, but can be particularly difficult for invasive microbes. The microbiologist's credo 'Everything is everywhere, but, the environment selects,' infers that microbial invasions are relatively continuous with success of population establishment dependent on environmental conditions. Therefore, environmental factors should be instrumental in predicting invasion success and establishment for microbial invaders. Prymnesium parvum, a toxigenic marine unicellular eukaryote, has invaded many freshwater systems throughout the southern and southwestern US. Like many invading species it can potentially wreak havoc in the invaded system, in this case, leading to massive fish kills during blooms. We've been monitoring P. parvum abundances in Lake Texoma (OK-TX) since the 2004 invasion and recently adopted qPCR as...
The growth rate hypothesis (GRH) proposes that variation in organismal C : N : P ratios is associ... more The growth rate hypothesis (GRH) proposes that variation in organismal C : N : P ratios is associated with growth rate due to differential allocation to P-rich ribosomal RNA to support growth. A further extension of the GRH proposes that this variation is associated with the structure of ribosomal (r)DNA genes (e.g., promoter-enhancer sequences in the rDNA intergenic spacer [IGS]) that influence the production rate of rRNA. To test these ideas, we examined growth rate, rDNA structure, RNA : DNA ratios, and elemental composition (C : N : P) in multiple clones of three Daphnia species (pulex, pulicaria, magna) in controlled laboratory experiments. Results show that a portion of the rDNA motif, consisting primarily of the IGS, shows considerable interspecific and intraspecific length variation. Significant interspecific differences in all parameters were found, while significant intraspecific (clone) effects were detected only for RNA : DNA ratios and growth rate. As predicted by the GRH, there were significant positive correlations between RNA : DNA ratio and either growth rate or rDNA/IGS length, and a significant positive correlation between rDNA/IGS length and growth rate, when clonal means for all three species were examined. However, no clear-cut relationships between RNA : DNA and either C : P or N : P were observed for any of the three species. Likewise, no discernible intraspecific relationships between growth rate and either C : P or N : P were detected. These preliminary findings suggest that further study of elemental composition, nucleic acid content, and growth rates of organisms may lead to a clearer understanding of the role of stoichiometric constraints in influencing the ecology and evolution of natural populations.
The role of stoichiometric food quality in influencing genotype coexistence and competitive inter... more The role of stoichiometric food quality in influencing genotype coexistence and competitive interactions between clones of the freshwater microcrustacean, Daphnia pulex, was examined in controlled laboratory microcosm experiments. Two genetically distinct clones of D. pulex, which show variation in their ribosomal (r)DNA structure, as well as differences in a number of previously characterized growth-rate-related features (i.e., life-history features), were allowed to compete in two different arenas: (1) batch cultures differing in algal food quality (i.e., high vs. low carbon:phosphorus (C:P ratio) in the green alga, Scenedesmus acutus); (2) continuous flow microcosms receiving different light levels (i.e., photosynthetically active radiation) that affected algal C:P ratios. In experiment 1, a clear genotype · environment interaction was determined with clone 1 out-competing clone 2 under high nutrient (i.e., low food C:P) conditions, while the exact opposite pattern was observed under low nutrient (i.e., high C:P) conditions. In experiment 2, clone 1 dominated over clone 2 under high light (higher C:P) conditions, but clonal coexistence was observed under low light (low C:P) conditions. These results indicate that food (nutrient) quality effects (hitherto an often overlooked factor) may play a role in microevolutionary (genotypic) responses to changing stoichiometric conditions in natural populations.
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