Research Description:

Quantifying Infection Prevalence in Sexual and Parthenogenetic Populations of the Freshwater Snail Campeloma limum

Sexual reproduction is found in over 99.9% of multicellular organisms, and while many evolutionary theories have been put forth to explain the origin and maintenance of sex, there is little empirical evidence to support any of them. Parthenogenesis is a form of asexual reproduction where females produce unfertilized eggs that develop into new individuals. The "two-fold cost of sex" suggests that parthenogens should have twice the reproductive rate of sexuals because it requires two sexuals to produce the same amount of offspring as one parthenogen. Nonetheless, sexual reproduction remains widespread.

I will use the freshwater snail Campeloma limum as a model organism for one theory, the Red Queen Hypothesis. The Red Queen hypothesis suggests that organisms employing sexual reproduction can evolve to escape parasites by constantly recombining their DNA while asexuals cannot because their genomes are not recombined and therefore evolve much slower. The Red Queen hypothesis predicts that parthenogens will only be found in areas with little to no parasites because they are unable to avoid overwhelming infection. Where parasites are present, it is predicted that infection will be greater for hosts with common genotypes while those with uncommon genotypes have a lower incidence of infection. This is expected because parasites will have had greater exposure to common genotypes (co-evolution) for many generations as opposed to uncommon genotypes.

When parasites are found, they will be preserved in alcohol and brought to Dr. Ellis Greiner for staining and identification, when possible. There is little documentation of both C. limum and its parasites, so I propose to identify general morphologies rather than identify species which have never been described.  The ultimate goal of quantifying infection prevalence and identifying specific morphologies is to compare infection in sexual populations vs. parthenogenetic populations as a means of testing the Red Queen hypothesis.