Effects of pentachlorophenol on predator avoidance behavior of the rotiferBrachionus calyciflorus

Intra- and interspecific interactions among rotifers are predominantly regu lated by contact chemo- and mechanoreception. There is no evidence that pre datory rotifers orient to their prey from a distance. As a result, the enco unter rate between predators and prey is heavily dependent upon the swimmin g speed of each species. Thus, rotifers may alter their probability of enco untering predators by reducing their swimming speed. However, this predator defense mechanism of the rotifer Brachionus calyciflorus is reversed by su blethal exposure to the toxicant pentachlorophenol. Swimming speed of B. ca lyciflorus was tested with the combined stresses of predation by Asplanchna girodi and sublethal concentrations of pentachlorophenol. A mathematical m odel was then developed to assess the effects of changes in B. calyciflorus swimming behavior on its predation risk. A significant interaction was fou nd between the presence of the predator and pentachlorophenol on B. calycif lorus swimming speeds. In the absence of toxicant, B. calyciflorus swam up to 20% slower in the presence of the predator, indicating a predation defen se mechanism capable of reducing encounter rates. However, sublethal pentac hlorophenol exposure caused a 30% increase in swimming speed, resulting in an increase in predation risk of up to 50%. These results indicate that sub lethal pentachlorophenol toxicity may adversely affect the ability of B. ca lyciflorus to avoid predation, thereby reducing its fitness. (C) 1999 Elsev ier Science B.V. All rights reserved.