CYTOLOGICAL EVIDENCE OF SPONTANEOUS ANDROGENESIS IN THE FRESH-WATER CLAM CORBICULA-LEANA PRIME

Cytological observations and DNA microfluorometry of the hermaphrodite freshwater triploid clam Corbicula leana revealed unusual androgeneti c development as follows: (1) the maternal genome of zygotes was extru ded as two polar bodies just after karyokinesis of the first meiosis, (2) only chromosomes derived from one male pronucleus constituted the metaphase of the first cleavage of zygotes, (3) DNA content of 7-day-o ld veliger larvae was identical to the somatic cells of the parent. Th is spontaneous androgenetic process in C. leana zygotes is the first c ase in the phylum Mollusca and may be related to the specialized mode of reproduction; i.e. hermaphroditism and self-fertilization.