Chemotaxis and Sexual Behavior in Chlamydomonas *

Intraspecific chemotaxis between gametes was demonstrated in Chlamydomonas moewusii Gerloff var. rotunda nov. var. which was previously used as C. sp. 24 (Tsubo Y. 1957). a heterothallic isogamous species from Japan. The reaction is unidirectional; the “+” gametes are attracted by the “—” gametes or cell‐free supernatant of medium in which the :“‐” gametes were suspended. In a study with 4 other isogamous heterothallic Chlamydomonas — C. moewusii Gerloff, C. eugametos Moewus, C. reinhardi Dangeard, and C. morewusii Gerloff var. tenuichloris nov. var. — none of them revealed any intraspecific chemotactic behavior. However, as with the “—” gametes of C. moewusii var. rotunda , both mating types of C. moewusii, C. eugametos , and C. moewusii var. tenuichloris were interspecifically attracted by the supernatant of the “—” culture of C. moewusii var. rotunda . Only C. rein‐ hardi showed no chemotactic behavior in intra‐ or interspecific combinations. Although chemotaxis occurred in the above‐mentioaed combinations, neither agglutination nor pairing ner zygete formation followed at all in the same combinations. The“;–” cells of C. moewusii var. rotunda killed by osmium vaper and then washed no longer produced the chemotactic agent, but did agglutinate with living “+” cells. Therefore, evidently, chemo‐taxis is a separate step from agglutination and zygote‐for‐mation yet does not seem necessary in the mating of isoga‐mous Chlamydomonas . Nonetheless, since this activity appears not in the vegetative but in the gametic stage, it seems to concern the sexual activity of the cells. In preliminary studies the chemotactic agent produced by C. moewusii var. rotunda was shown to be volatile.