Sexual reproduction in desmids with special reference to micrasterias thomasiana var. Not at a (nordst.) gronblad

Abstract

Strains of several forms of Micrasterias t ho mas ¡ana, isolated in Tasmania and Victoria, conjugated when mixed in all combinations. Homothallism was not detected and rarely were both mating strains present in one locality. Conjugation, preceded by an initial pairing and subsequent cell division, takes place between offspring of this division, either within or between parental groups. Conjugants, invested by a mucilage envelope, secrete a pinkish mucilage medially, in which a conjugation cylinder differentiates. Its relationship to conjugation structures in other species is discussed. Conjugation is anisogamous. The spiny zygospore has at least three walls and an undifferentiated operculum of the exospore facilitates germination. Only one gone is produced. Meiosis occurs at or immediately preceding germination. Most chromosomes are too small to reveal details of centromeric organization but two longer chromosomes are apparently sub-telocentric. Meiosis is at least partially asynchronous. A presumably haploid complement of about 40 chromosomes is likely. The suitability of sexual procedures for taxonomic criteria is explored. © 1981 Taylor & Francis Group, LLC.