FERTILIZATION AND SPERM COMPETITION IN THE NEMATODE CAENORHABDITIS-ELEGANS

The process of fertilization by hermaphrodite and male sperm is described. In the hermaphrodite fertilization occurs in the spermatheca by the first sperm to contact the oocyte. Other sperm that contact the oocyte are swept into the uterus but they crawl back into the spermatheca to fertilize subsequent oocytes so that every sperm fertilizes an oocyte. Not every oocyte is fertilized because oocytes are made in excess. Fertilization triggers active movement of oocyte cytoplasmic granules. Sperm penetration is not required for this activation because fertilization-defective mutant sperm trigger activation without penetration. When males copulate with hermaphrodites, their sperm is deposited in the uterus beneath the vulva. These sperm crawl up the uterus to the spermatheca where they displace the hermaphrodite sperm from the spermathecal walls and preferentially fertilize the oocytes. This preferential fertilization appears to be due in part to inhibition of hermaphrodite sperm fertility by the male sperm. The male sperm competition ensures male sperm utilization and thus some outcrossing in a population of predominantly self-fertilizating hermaphrodites. © 1979 Academic Press, Inc. All rights reserved.