Research: Genetics of Sperm Competition
What is sperm competition?
Female Drosophila melanogaster can mate more than once and they have the ability to store
and use sperm from several males. When males mate with non-virgin females, the sperm they
transfer to the female must compete for access to unfertilized eggs with sperm already present
in the female's reproductive tract. This is what is meant by sperm competition.
Why is sperm competition important?
Males that are especially successful at sperm competition are able to sire more offspring and
enjoy higher fertility. Since this competitive ability has a genetic component, more competitive
males will enjoy a higher fitness; their offspring and their genes are able to persist at the
expense of males whose sperm lack this competitive ability.
Quantitative data for sperm precedence and genes of major effect
Prout & Bundgaard (1977) demonstrated that different laboratory strains of D.
melanogaster differed in their sperm competitive ability. An analysis of quantitative genetic experiments
(Hughes 1997) indicates that just a few loci that reside on chromosome III have large effects on
sperm competitive ability.
How do you design an experiment to test sperm competitive ability?
These experiments involve allowing single virgin females to mate with two different males
consecutively and observing the phenotypes of the offspring she produces. Each female and
one of the males is homozygous recessive for the ebony body color mutation. The other male
is wild type for body color. An ebony female (e/e) X ebony male (e/e) mating will have ebony
offspring (e/e), while offspring from an ebony female X wild type male (+/+) mating will have
wild type body color (e/+). Therefore, by counting the body colors of the offspring, you can
determine which male fathered the most offspring.
How to test chromosome III for sperm precedence?
By using special balancer stocks of mutant flies in a series of crosses, it is possible to generate
different lines of flies that have different third chromosomes. Flies within a line have identical
third chromosomes, but flies between lines have different third chromosomes. Males from
these lines have wild type body color, and they are used in sperm competition experiments to
determine which lines have a high sperm competitive ability and which ones a low ability.
| Department of Animal Biology | School of Integrative Biology | University of Illinois |
Created 08/01/01
Updated 08/01/01