A mutation ofEuplotes vannuscausing induction of intraclonal conjugation (selfing) in low [K+]o

A newly discovered recessive mutation,clk, in the marine ciliateEuplotes vannusis responsible for induction of intraclonalconjugation atlow, i.e. <2 instead of 10 mM [K+]o. Heredity was assured by crosses to standard clones and by backcrosses. Pairing inclkclones is prevented by K+at 2 mM, by Rb+and Cs+and Cs+at 4 mM, not by Li+, NH4+, and TEA+up to 10 mM. Clones with theclkphenotype were found in several natural populations.