TIME-LAPSE STUDIES OF CONJUGATION IN COSMARIUM BOTRYTIS: II. PSEUDOCONJUGATION AND AN ANISOGAMOUS MATING BEHAVIOR INVOLVING CHEMOTAXIS

Abstract

Techniques were devised for the continuous observation of the 24-hour process of cell pairing and gamete fusion in the morphologically isogamous heterothallic desmid Cosmarium botrytis by the use of time-lapse ciné-photomicrography. Several stages of early conjugation are described and their duration measured. Many pairings are temporary and the cells dissociate after a few hours. This phenomenon is termed pseudoconjugation. Dissociation is frequently caused by the nuclear or cell division of one partner. By the use of morphological variants to determine the mating type of individual cells observed in a mixture of two mating types, an anisogamous behavior during pairing was noted. In any particular cross between two compatible clones, cells of one clone become relatively immobile or passive during conjugation while those of the other clone are attracted towards them, probably by chemotaxis. This anisogamous behavior is not rigidly linked with mating type since some plus clones are either passive or chemo-tactically active, depending upon which minus clone they are crossed with. An interim explanation of the mechanism is given.NoteThe term “anisogamous” is usually defined as a difference in size or morphology between compatible gametes. In this paper the definition is extended to cover differences in the mating behavior of gametes that are otherwise identical.