Monterey Bay Aquarium Research Institute
Marine Botany

Pseudo-nitzschia Sexual Reproduction

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Why Sexually Reproduce?

After diatoms within the genus Pseudo-nitzschia (as well as most other genera of diatoms) have vegetatively multiplied for an extended period of time, the cells ultimately face the problem of size reduction. Sexual reproduction is a diatom's response to this problem. Size can be restored through the formation of an auxospore following meiosis and sexual reproduction. A specialized zygotic cell called an auxospore swells in sexually mature cells and act to restore size. The physiological basis for how a diatom is able to switch from vegetative growth to sexual reproduction is not entirely known.

Centric vs. Pennate Diatoms

Those species of pennate diatoms within the genus Pseudo-nitzschia differ in their method of sexual reproduction when compared to centric diatoms. Sexual reproduction in centric diatoms involves oogamy whereupon the large non moving female gamete is fertilized by small, flagellate sperm (thought that chemotaxis plays a part in recognition). Sexual reproduction in Pseudo-nitzschia, on the other hand, involves morphologically indistinguishable gametes and thus is called isogamous.

Sexual Reproduction

  • Differentiation of parent cells into gametangia
  • Pairing of parent cells = gametangiogamy, lie valve to valve in a parallel fashion
  • Next state is called gametogenesis: each cell divides meiotically forming spherical gametes.
    • Each gametangium yields two morphologically isogamous nonflagellated gametes with anisogamous behavior.
    • One gametangium produces two active gametes while the other produces two passive gametes.
  • The frustules completely open, allowing both active gametes to move via amoeboid action towards the passive gametes in the other gametangium.
  • Each gamete fuses with the nearest one in the other gametangium, forming a spherical zygote in 1-2 minutes.
    • Gametes were unable to fuse if they had lost contact with their parent frustule: substrate probably needed for amoeboid movement
  • Two auxospores are formed from the two sets of gametes.
    • They remain attached to only one parent frustule (or may not be associated to any frustule).
  • Gamete formation to appearance of initial cells (auxospores) takes 2-4 days (entire process of sexual reproduction).

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copyright Jennifer Shin 1999.

Last updated: Feb. 05, 2009