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Intra- and interspecific interactions among rotifers are predominantly regulated by contact chemo- and mechanoreception. There is no evidence that predatory rotifers orient to their prey from a distance. As a result, the encounter rate between predators and prey is heavily dependent upon the swimming speed of each species. Thus, rotifers may alter their probability of encountering predators by reducing their swimming speed. However, this predator defense mechanism of the rotifer Brachionus calyciflorus is reversed by sublethal exposure to the toxicant pentachlorophenol. Swimming speed of B. calyciflorus was tested with the combined stresses of predation by Asplanchna girodi and sublethal concentrations of pentachlorophenol. A mathematical model was then developed to assess the effects of changes in B. calyciflorus swimming behavior on its predation risk. A significant interaction was found between the presence of the predator and pentachlorophenol on B. calyciflorus swimming speeds. In the absence of toxicant, B. calyciflorus swam up to 20% slower in the presence of the predator, indicating a predation defense mechanism capable of reducing encounter rates. However, sublethal pentachlorophenol exposure caused a 30% increase in swimming speed, resulting in an increase in predation risk of up to 50%. These results indicate that sublethal pentachlorophenol toxicity may adversely affect the ability of B. calyciflorus to avoid predation, thereby reducing its fitness. |
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