Predator-induced trophic shift of a free-living ciliate: parasitism of mosquito larvae by their prey.

Larvae of the treehole mosquito, Aedes sierrensis, release a waterborne factor that induces morphogenesis of one of their prey, the tetrahymenid ciliate Lambornella clarki. Induced free-living trophonts of L. clarki undergo a synchronous response in which cells divide and transform into parasitic cells (theronts) that encyst on larval predators. Parasitic ciliates penetrate the cuticle, enter the hemocoel, and ultimately kill their predator-host. In nature, this trophic shift can lead to predator extinction and dramatic changes in microbial populations. Facultative parasitism by this polymorphic ciliate may have evolved as an antipredator strategy. The experimentally inducible parasitic response of L. clarki provides a novel model for studying cellular morphogenesis of ciliated protozoa.