HOMOTHALLIC AUXOSPORULATION INPSEUDO-NITZSCHIA BRASILIANA(BACILLARIOPHYTA)

8 pages, 5 figures, 3 tables
Most pennate diatoms are allogamous, and various types of mating systems have been described. In Pseudo-nitzschia, reproductive stages have been identified in some species, and it is generally accepted that the genus is mainly heterothallic. Here we report homothallic auxosporulation of Pseudo-nitzschia brasiliana Lundholm, Hasle et G. A. Fryxell. To our knowledge, this is the first verified description of homothallic sexual reproduction in the genus. Auxospore formation was observed in all 16 subclones derived from three initial clonal cultures of P. brasiliana. Pairing was followed by production of two gametes per gametangium, which fused to give two zygotes. Each zygote (early auxospore) was initially spherical and adhered to one girdle band of the parental frustule. The two auxospores tended to expand parallel to each other and perpendicular to the parental frustule. Elongation was synchronous, slightly asynchronous, or totally asynchronous. The entire process of sexual reproduction, from gamete formation to the appearance of the initial vegetative cells, took 2–4 d. The occurrence of sex in a homothallic species seems an advantageous life strategy for this species in that any encounter between cells of the right size class is potentially sexual
This study was supported by the EC funded Research Project SEED (Life cycle transformations among HAB species, and the environmental and physiological factors that regulate them), GOCE-CT-2005-003875, and the CRA (Centre de Referencia en Aquicultura, CIRIT-Generalitat de Catalunya, Spain). E. Garcés work was supported by a Ramon y Cajal contract of the Spanish Ministry of Education and Science. S. Quijanós work was supported by a PROMEP grant (Mexico), Colima University