Selective cannibalism in the rotifer asplanchna sieboldi: contact recognition of morphotype and clone.

Populations of A. sieboldi reproduce primarily by diploid femal parthenogenesis. Females may exhibit a pronounced, nongenetic polymorphism which is controlled by the diet. The cruciform and especially the campanulate morphotypes are larger than the saccate morphotype and are cannibalistic. Direct observations of various predator-prey interactions between the different morphotypes of two taxonomically distinct clones show that the feeding responses of cannibals after actual prey contact are predictable and extremely selective. Companulates from clone B respond regularly to saccate but only rarely to cruciform or campanulate clonemates; the same predators typically respond to cruciforms and campanulates from clone C. Cruciforms from clone C rarely respond to saccate and cruciform clonemates but readily attack all morphotypes from clone B. In contrast, campanulates from clone C show no selectivity. Morphotype- and clone-specific recognition responses, which are mediated by coronal contact chemoreceptors, permit efficient prey discrimination and protection withotu involving prey handling or development of energy-demanding, defensive structures, such as the body-wall outgrowths of the cruciform morphotype. Selective feeding of cannibals may increase the fitness of a clone, both by effecting a more adaptive distribution of its morphotypes and by enhancing its ability to compete directly and indirectly with cooccurring clones. The magnitude of cannibalism in this rotifer may be dependent upon a complex suite of heterogeneous predator-prey interactions and greatly affected by shifting densities and distributions of different clones and female morphotypes.