Studies of Alexandrium Catenella (Dinophyceae)gametes

The life cycle of Alexandrium catenella (a Paralytic Shellfish Poison-producing dinoflagellate) facilitates bloom initiation, bloom decline, and species dispersal. Little is known of their gametes because they are indistinguishable from vegetative cells by morphology or ploidy. In this thesis study, (+) and (-) mating A catenella cultures (NEPCC #743 and #744) were isolated from Toquart Bay, Barkley Sound, BC. These were maintained in enriched Barkley Sound seawater: artificial seawater medium induced aberrant cell forms and natural water from a local site produced slower growth and reduced the percentage of culture in chains. The sexual cycle was induced by transferring cultures into N/10 medium. Cultures were mixed in stationary phase and cysts appeared in 10-12 d, suggesting that gametes were present after ~6 d. Encystment rates were highest in N-deplete medium (15.0%); but encystment was possible in N-replete medium, in many containers, at all times of the year, and was not affected by salinity (26 vs. 31). Blue light and germanium dioxide appeared to reduce encystment. Single cells were isolated into single wells and videotaped daily. The following was learned by comparing non dividing single cells (ND) which are potentially gametes, and dividing cells (D) which are therefore vegetative cells: 1) 17 of the 92 isolated single cells were ND; 2) ND cells survived for 2-26 d; 3) the size range of ND cells (27-51 x 24-48 pm) overlaps that of D cells (25-55 x 24-49 pm); 4) ND and D cells before their division were longer than wide, and D cells after division were wider than long; 5) before dying, 4 ND cells gained in volume and 7 ND cells lost volume, whereas all D cells gained in volume prior to dividing; 6) on average, #744 cells were longer and wider than #743 cells, but the ranges overlapped. These findings explain why pairing has been infrequently observed between unequal sized gametes, but confirms that A. catenella pairing should be classified as isogamous. Single cells were isolated into single wells. After 5-7 d, ND and D cells were fixed and then labeled with the lectin FITC-Con A. No surface differences in labeling were observed between ND and D cells or between mating type. Labeling was typically pale and diffuse with infrequent bright spots and no flagellar labeling. Differences may be discovered if studies were repeated at lower lectin concentrations, cells were labeled live, or larger sample sizes were used.Science, Faculty ofEarth, Ocean and Atmospheric Sciences, Department ofGraduat