VARIATION IN THE SEXUAL-BEHAVIOR OF NATURAL CLONES OF ACHNANTHES-LONGIPES (BACILLARIOPHYTA)

Monoecious, bisexual and unisexual clones of Achnanthes longipes were isolated from the Black Sea and studied in laboratory culture. Clones differed in their growth characteristics: in monoecious clones the cel ls formed tufted aggregations while in other clones they were more dis persed. Bisexual and unisexual clones exhibited intraclonal (monoeciou s) reproduction but only at a very low frequency and usually within a more restricted size range than in monoecious clones. Interclonal cros ses were made in all possible pairwise combinations. Abundant auxospor ulation took place in all crosses, except where unisexual clones of th e same sex were incubated together. Auxosporulation was more vigorous and occurred over a wider size range in interclonal crosses than durin g monoecious reproduction. Sexual reproduction is isogamous. In the co mmonest pattern of auxosporulation, two paired gametangia each produce two gametes, which fuse to give two auxospores. More rarefy (9% of pa irs), the gametangia produce only one gamete apiece, and hence only on e auxospore. In addition, very small cells can enlarge vegetatively, a lthough genetic or cytological damage sometimes compromises their long -term viability.