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The World of Protozoa, Rotifera, Nematoda and Oligochaeta

Ref ID : 3675

Barry J. Wicklow; Developmental Polymorphism induced by Intraspecific Predation in the Ciliated Protozoon Onychodromus quadricornutus. J.Protozool. 35(1):137-141, 1988

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The hypotrich ciliate Onychodromus quadricornutus is remarkable in its potential for voluminous size (up to 900 µm in length), its possession of a unique set of four dorsal spines or horns, and its capability to express two kinds of developmental polymorphism induced by intraspecific predation. Cell length frequencies in replicates of a well-fed clone show normal distributions; starvation followed by intraspecific predation, however, induces cell within a clone to transform into two size classes: small lanceolate cells and cannibal giants. Induction experiments indicate that a substance released by cannibal giants stimulates defensive spine growth in clonemates within 24 hr. Giants can also induce spine growth in non-clonemates. Furthermore, O. quadricornutus cells exposed to the predacious ciliate Lembadion magnum also develop hypertrophied spines. Selection experiments show that conspecific giants prey on cells with undeveloped spines (<20 µm in length) to a much greater extent than on cells with developed spines (>40 µm in length). Transformation of a population of similarly sized O. quadricornutus cells into two different size classes may function to increase the range of potential prey sizes available to the O. quadricornutus population; hypertrophied spines appear to function as an inducible defense against intermittent predators appearing in the system including conspecific giants. This is the first reported case of a defensive developmental polymorphism induced by intraspecific predation.