Dinoflagellate life history

Sexual reproduction is known to occur in very few living dinoflagellates. Asexual (vegetative) reproduction predominates and involves a division of the cell into two halves by binary fission. Details of the life

Life History Cell

Theca shed

Hypnozygote

Fig. 10.5 Idealized life cycle involving sexual reproduction and cyst formation. Section A, cells are motile and haploid; section B, cells are motile and diploid; section C, cells are non-motile (except excysted cell on left) and diploid. (Reproduced from Stover et al. in Jansonius & McGregor 1996, vol. 2, pp. 641-750 (with the permission of the ASSP Foundation).)

Theca shed

Hypnozygote

Fig. 10.5 Idealized life cycle involving sexual reproduction and cyst formation. Section A, cells are motile and haploid; section B, cells are motile and diploid; section C, cells are non-motile (except excysted cell on left) and diploid. (Reproduced from Stover et al. in Jansonius & McGregor 1996, vol. 2, pp. 641-750 (with the permission of the ASSP Foundation).)

cycle can vary considerably, particularly in the sexual part of the cycle, and a generalized life cycle is described here (Fig. 10.5). With the exception of Polykrikos (Fig. 10.6d) and Noctiluca (Fig. 10.6e), the vegetative motile stage the schizont has a full chromosomal compliment and is haploid. Once formed, the zygote enlarges, the cell wall thickens (at this stage it is known as the planozygote) and it looses motility. In the hypnozygote stage the cytoplasm contracts, the cyst forms and the flagella are lost. The cytoplasm may remain dormant in the cyst for hours to years during which time the first and occasionally second meiotic divisions occur. The resultant cells will emerge through the archeopyle and growth and vegetative division are initiated. In laboratory culture withholding nutrients or reducing temperature and light levels can induce sexual reproduction. Though cysts can form in the schizont, the majority of fossil dinoflagel-late cysts are believed to be hypnozygote cysts. Many dinoflagellate cysts remain dormant on the sea floor through the winter. During this period the surrounding thecal plates may drop away and begin to decay. With the amelioration of conditions in spring, the motile stage excysts through the archaeopyle to leave a resistant cyst for the fossil record.

Was this article helpful?

0 0
Freehand Sketching An Introduction

Freehand Sketching An Introduction

Learn to sketch by working through these quick, simple lessons. This Learn to Sketch course will help you learn to draw what you see and develop your skills.

Get My Free Ebook


Post a comment