Browsing by Author "Kasimatis, Katja"

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    Differential lifespan effects due to mating in two strains of Caenorhabditis elegans
    Lancaster, Ruben; Kasimatis, Katja; Phillips, Patrick
    Mating is vital for sexually reproducing species, yet the ideal mating strategy for males and females can differ. The ensuing conflict between the sexes – namely sexual conflict – results in a decrease in population level fitness. The degree of sexual conflict can be affected by the behavior, physiology, and life history of a population. Previous studies in the nematode Caenorhabditis elegans have shown that mating causes lifespan decreases in pseudo-females and hermaphrodites, which was taken as evidence of sexual conflict. However, it is still an open question whether variations in mating condition and strain type can affect the degree of sexual conflict and lifespan decrease. To investigate whether the effects of mating on lifespan persisted in other conditions, I conducted population-based mating assays in two different strains of C. elegans using both natural and male-skewed sex ratios. Counter to expectations, I found no effect of mating in a wild isolate of C. elegans, while virgins from a canonical strain had a decreased lifespan relative to their mated counterparts in group mating conditions but not individual mating conditions. Skewed sex ratios during mating had no effect on lifespan. My results highlight the need for the life history of populations to be taken into account when studying the effects of mating.
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    The Influence of Sexual Selection and Sexual Conflict on the Evolution of Post-Insemination Dynamics
    (University of Oregon, 2019-09-18) Kasimatis, Katja; Phillips, Patrick
    Sexual reproduction is a fundamental process that structures populations and modulates interactions between species. The reproductive process is shaped by selection acting on the variance in mating success. Additionally, conflict between the sexes over the mechanisms by which mating success is optimized effects reproduction. Selection can also act in a sex-specific manner outside of the reproductive process and drive a different class of sexual antagonisms. To understand how sexual conflict shapes evolution within and between the sexes, the action of selection must be connected to the lifecycle of an individual. Such a lifecycle-explicit framework allows for quantitative measurements of sex-specific selection, sexual conflict, and genetic load. Here I connect the action of selection with the appropriate stage of the lifecycle to determine how conflict between the sexes contributes to genome evolution. Using theoretical approaches, I examine if sexually antagonistic viability selection can create genomic divergence between the sexes. I find that selection must be strong to generate measurable divergence, which produces a high genetic load. Additionally, I show that sampling variance can account for much of the signal attributed to sexually antagonistic selection in the literature. Using experimental approaches, I manipulate sex-specific selection acting during the gametic phase to determine the molecular components of male fertilization success. I develop Caenorhabditis nematodes as a new model system for studying post-insemination reproductive interactions. Contrary to expectation, I find that nematode sperm proteins are hyper-conserved at the sequence level and rapidly evolving at the gene family level. This result suggests an alternative signature of sex-specific selection and conflict. Additionally, I develop a genetic tool for isolating sperm dynamics. This sterility induction system is the first external, non-toxic, reversible sterility induction system in animals. Together my dissertation highlights how the genomic signatures of sexual selection and conflict are complex and require explicit empirical testing to validate both the phenotype and action of selection. Such complexity indicates that evolutionary systems biology approaches will be the most informative way to move the field forward and establish the importance of sexual conflict in shaping evolution. This work includes published and unpublished coauthored material.