The toxicological effects of pyraclostrobin on the energy allocation pattern of the freshwater gastropod, Lymnaea stagnalis
Fidder, Bridgette N.
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With fungicide use on the rise in the last decade, it has become increasingly important to investigate their effects on non-target species. As aquatic species in some instances are unable to escape habitat contamination, it is important to examine these organisms for potential toxicity. Long-standing aquatic invertebrate models for ecotoxicological testing have included insects (i.e. Chironomus riparius) and especially crustaceans (i.e. Daphnia magna); however, gastropods have been recently identified as a promising model species for toxicity testing. We used the great pond snail, Lymnaea stagnalis (Lymnaeidae), currently under OECD consideration, as a model species to investigate the effects of a common but understudied fungicide, pyraclostrobin, on their energy allocation patterns. In the first study, we aimed to determine the effects of pyraclostrobin on various life stages in L. stagnalis to examine specific effects on maintenance energy (routine behavior), production energy (reproduction and growth), and energy stores (proteins, lipids, and carbohydrates). We first determined baseline toxicity of juveniles and adults to pyraclostrobin, as data was lacking for this specific species. Juvenile snails exposed to pyraclostrobin experienced a decrease in feeding rate and an increase in behavioral avoidance. During a reproduction study, we found that calculated environmentally relevant sublethal concentrations did not elicit significant effects on reproductive output. However, when comparing hatching success of L. stagnalis from directly and maternally + directly exposed egg masses, a significant difference in time to hatch was observed in hatchlings exposed to identical pyraclostrobin concentrations. Egg masses collected from maternally-exposed adults also had significant differences in protein and carbohydrate content. Pyraclostrobin clearly influenced behavior, feeding rate, hatching success, and macronutrient content of Lymnaea stagnalis. These results provide important insight into an understudied but potentially harmful toxicant. Animals should naturally select diets of the highest quality to obtain maximal energy while devoting the least amount of time and energy to the process. By offering the common laboratory diet only, ecotoxicology tests may be consistently under- or over-estimating toxicant sensitivity. The second study aimed to evaluate the effect of diet quality on sensitivity to pyraclostrobin using growth rate of Lymnaea stagnalis fed common laboratory, high nutrient, and combination diets. We also measured the macronutrient content of snails raised on the multiple diets to determine if diet and pyraclostrobin interacted synergistically to alter energy allocation patterns. Finally, we tested snails for an indication of the ability to select energy rich diet using a dietary preference study. Snails fed high nutrient and combination diets grew faster than snails fed standard lettuce for 54 days. Both juvenile and adult snails fed either the high nutrient or combination diets were significantly more tolerant to pyraclostrobin than snails fed lettuce only. When measured for macronutrient content, snails raised on high nutrient and combination diets had significantly higher carbohydrate content than snails fed lettuce. Snails used in the dietary preference study did not exhibit a clear choice in choosing the diet with higher nutritional content. Dietary composition clearly influences growth rate, sensitivity, and macronutrient content of Lymnaea stagnalis. These results imply that additional consideration should be given to diet quality in laboratory toxicity tests.