SPERM PRECEDENCE IN A HERMAPHRODITIC NEMATODE (CAENORHABDITIS-ELEGANS) IS DUE TO COMPETITIVE SUPERIORITY OF MALE SPERM

When male and hermaphrodite Caenorhabditis elegans mate, the male's sp erm outcompete the hermaphrodite's own sperm and fertilize a majority of the offspring. Here, we investigate the mechanism of male sperm pre cedence. We rule out the possibility that male sperm are stronger and more competitive because they are activated later than hermaphrodite s perm. We also find that a previously known gender difference in sperm activation does not influence sperm competition. Male sperm, rinsed fr ee of seminal fluid, retained the capacity to take precedence after ar tificial insemination. Therefore, we conclude that male sperm themselv es are competitively superior to hermaphrodite sperm. This trait maxim izes outcrossing after mating and may increase both genetic diversity and heterozygosity of offspring whose parents, due to self-fertilizati on, may be highly homozygous.