Predator-induced morphological defence in ciliates: interclonal variation for sensitivity to the inducing factors

This study brings the first evidence for the interclonal variation in the expression of predator-induced morphological defence in ciliates. The degree of response to the ciliate predator Stylonychia mytilus was compared in 18 clones of Euplotes octocarinatus. Although all the examined clones were inducible, they attained similar level of the response at a different “dose” of inducing factor. One of the clones maintained the “induced form” permanently, i.e. in the absence of any predator. Furthermore, comparing the effects of two different predators S. mytilus and a turbellarian Stenostomum sp. revealed differences among closely related clones in their relative responses to these predators. The degree of response in a given clone to one predator species did not preclude its response level to the other one suggesting that the expression of the defence to different predators might change independently. Our findings indicate that there is genetic variation for sensitivity to the inducing factors in Euplotes and hence the possibility for selection on this variation.