Differences in predation among morphotypes of the rotifer Asplanchna silvestrii

1. Interactions were observed between three morphotypes of the predatory ro tifer Asplanchna silvestrii and six different prey (Brachionus plicatilis, B, rotundiformis, B, pterodinoides, B, satanicus, Hexarthra jenkinae and co pepod nauplii) to understand the differences in feeding abilities among mor photypes that may have led to the evolution of this predator polymorphism T he outcome of predation events was affected significantly, both by predator morphotype and prey type. Predator morphotypes also interacted differently with different prey types. 2. The two smaller morphotypes, the saccate and the cruciform, responded si milarly to prey overall, except that the smallest morphotype (saccate) was unable to ingest the most mobile prey (nauplii) and less able to ingest rel atively large prey (B. plicatilis). The largest morphotype, the campanulate , had the highest encounter rate with prey, but the lowest probability of a ttack after encounter, so that it consumed far fewer prey per feeding bout than did the smaller morphotypes. This may have been because campanulates p refer larger prey than used in this study. 3. Highly mobile prey (H, jenkinae and copepod nauplii) were much less susc eptible to predation than the less mobile Brachionus species. While evasive ness reduced attacks by saccates and cruciforms, campanulates did not have a significantly lower attack rate on H.jenkinae and copepod nauplii than on less evasive prey. Large body size moderately defended B, plicatilis again st ingestion by saccates only. The short-spined B, satanicus was the only p rey that was rejected after capture, resulting in lower ingestion probabili ties for B. satanicus than other brachionid prey.