Oocyte production and sperm utilization patterns in semi-fertile strains of Caenorhabditis elegans

Caenorhabditis elegans hermaphrodites are capable of producing hundreds of progeny. However, genetic and environmental factors can keep many animals from attaining their full reproductive potential. In these situations, efficient use of any functional gametes becomes more important for reproductive success. To learn about this aspect of C. elegans reproductive biology, we examined oocyte production and sperm utilization patterns in a unique collection of semi-fertile sperm function mutants.

In the mutants examined here, broods can be very small but sperm induced high levels of ovulation. Ovulation rates reach maximum levels between the first and second day of adulthood. Ovulations rates remain high during the reproductive period and gradually decline with age. These results further demonstrate a decoupling of the ability of sperm to fertilize oocytes and induce ovulation. We also observe that in our semi-fertile mutants the peak of successful fertilization events precedes the bulk of oocyte production. Mixing populations of functional and nonfunctional sperm under conditions without sperm competition also shows that functional sperm are utilized efficiently. Although overall brood size can be similar for different mutant strains, slight differences in the pattern of sperm utilization in these strains can lead to significant differences in resource utilization and population growth.

This study represents the first detailed description of oocyte and progeny production patterns over the entire reproductive period for wild-type and fertility impaired strains of C. elegans. The phenotype of our mutants provide an ideal system for studying sperm utilization patterns since they only affect one major process, the ability to fertilize oocytes. In semi-fertile mutants, the nature of the reproductive process and/or specific molecular mechanisms ensures that any functional sperm are utilized quickly. Only a fraction of the sperm produced by our semi-sterile mutants are functional as opposed to every sperm having a low but equal chance of fertilizing an oocyte. In addition to the number of progeny produced, the pattern of progeny production can have an important influence on the dynamics of population growth.