SPERM COMPETITION IN THE SIMULTANEOUS HERMAPHRODITE FRESH-WATER SNAILBIOMPHALARIA-GLABRATA (GASTROPODA, PULMONATA)

An isolated heterozygous Cc Biomphalaria glabrata produces, in strict self-fertilization involving C and c oocytes and spermatozoa, an exces s of pigmented progeny, when compared with the expected 3:1 Mendelian ratio. When isolated after insemination by an albino partner, an heter ozygous Cc snail shows for 17 days an expected 1:1 Mendelian ratio of pigmented and albino progeny; after the 17th day, self-fertilization i s progressively resumed. When fertilized by only c spermatozoa, the tw o kinds (C and c) of oocytes play a similar role and do not explain th e excess of pigmented progeny obtained by selfing. After a similar pai ring (Cc x cc), the isolated albino parent also produces, from the 2nd to 20th day, a significant excess of pigmented progeny. These experim ental results confirm previous observations obtained from homozygous l ineages. In both homozygous strains (CC and cc), around 50% of spermat ozoa are apyrene or oligopyrene. C spermatozoa are significantly longe r than c spermatozoa; this difference, which is classically related to better kinetics, could explain the present results.