Morphotype-specific predation in the trimorphic rotifer Asplanchna silvestrii

Abstract

Several species of the predatory rotifer Asplanchna exhibit dramatic diet-induced trimorphism. The three morphotypes differ greatly in body shape and size, attributes that should affect predation ability. It has been hypothesized that these morphotypes evolved to exploit different prey assemblages in different environments. Here I compare the predatory behavior of the campanulate morphotype (the largest) to that of the cruciform morphotype (the intermediate) using crustacean and conspecific prey. These prey are known to induce production of the greatest proportion of campanulates. I hypothesize that the campanulate is better able to exploit these relatively large prey than are cruciforms. The campanulares did have higher ingestion rates with conspecific prey, but the ingestion rates of the morphotypes were not different with the crustacean prey, due to the campanulate's relatively low probability of attacking the crustacean prey. The campanulate attack probability is higher with both conspecific and crustacean prey than has been previously reported for campanulate A. silvestrii with smaller rotifer prey. While the campanulate handles both relatively large prey with comparative ease, and is more likely to attack these prey than smaller rotifer prey, the campanulate morphotype seems most effective at cannibalism due to its high preference for congeneric prey.