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

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Abstract
Populations of A. sieboldi reproduce primarily by diploid female parthenogenesis. Females may exhibit a pronounced, nongenetic polymorphism 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 2 taxonomically distinct clones showed that the feeding responses of cannibals after actual prey contact were predictable and extremely selective. Campanulates from clone B responded regularly to saccate but only rarely to cruciform or campanulate clonemates; the same predators typically responded to cruciforms and campanulates from clone C. Cruciforms from clone C rarely responded to saccate and cruciform clonemates but readily attacked all morphotypes from clone B. In contrast, campanulates from clone C showed no selectivity. Morphotype- and clone-specific recognition responses, mediated by coronal contact chemoreceptors, permitted efficient prey discrimination and protection without involving prey handling or development of energy-demanding, defensive structures such as the body-wall outgrowths of the cruciform morphotype. Selective feeding of cannibals could increase the fitness of a clone, by effecting a more adaptive distribution of its morphotypes and by enhancing its ability to compete directly and indirectly with co-occurring 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.
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