Morphotype-specific predation in the trimorphic rotifer Asplanchna silvestrii

Several species of the predatory rotifer Asplanchna exhibit dramatic diet-i nduced trimorphism. The three morphotypes differ greatly in body shape and size, attributes that should affect predation ability. It has been hypothes ized that these morphotypes evolved to exploit different prey assemblages i n different environments. Here I compare the predatory behavior of the camp anulate morphotype (the largest) to that of the cruciform morphotype (the i ntermediate) using crustacean and conspecific prey. These prey are known to induce production of the greatest proportion of campanulates. I hypothesiz e that the campanulate is better able to exploit these relatively large pre y than are cruciforms. The campanulates did have higher ingestion rates wit h conspecific prey, but the ingestion rates of the morphotypes were not dif ferent with the crustacean prey, due to the campanulate's relatively low pr obability of attacking the crustacean prey. The campanulate attack probabil ity is higher with both conspecific and crustacean prey than has been previ ously reported for campanulate A. silvestrii with smaller rotifer prey. Whi le the campanulate handles both relatively large prey with comparative ease , and is more likely to attack these prey than smaller rotifer prey, the ca mpanulate morphotype seems most effective at cannibalism due to its high pr eference for congeneric prey.