Sperm Competition in Nematodes Sperm Competition Craig LaMunyon , Assistant Research Professor S perm competition occurs when sperm from two individuals compete to fertilize eggs. I am studying the mechanism of sperm competition and how it affects the evolution of male and female traits. Sperm competition is a widespread phenomenon, occuring in almost every species. I study the mechanism of sperm competition in C. elegans and related nematode species.
Males are rare but readily mate with hermaphrodites.
In both C. elegans and its close relative, C. briggsae , male sperm displace the hermaphrodites' own sperm and predominate in fertilization. Using an artificial insemination protocol I developed to remove seminal fluid, I found that the male sperm take precedence in the absence of seminal fluid and that the male sperm cells themselves are competitively superior to hermaphrodite sperm. My investigations have shown that larger sperm crawl faster and physically displace smaller sperm from the sites of fertilization. Further, males that make larger sperm gain sperm precedence over males that make smaller sperm. Thus, sperm competition appears to have driven the evolution of sperm size in nematodes.