Stress can be a driving force for new evolutionary changes leading to local adaptation, or may be responded to with pre-existing, ancestral tolerance mechanisms. Using brachionid rotifers (microzooplankton) as a study system, I demonstrate roles of both conserved physiological mechanisms (heat shock protein induction) and rapid evolution of traits in response to ecologically relevant stressors such as temperature and hydroperiod. Rapid evolution of higher levels of sex and dormancy in cultures mimicking temporary waters represents an eco-evolutionary dynamic, with trait evolution feeding back into effects on ecology (i.e., reduced population growth). I also reveal that prolonged culture in a benign laboratory environment leads to evolution of increased lifespan and fecundity, perhaps due to reduction of extrinsic mortality factors. Potential mechanisms (e.g., hormonal signals) are suggested that may control evolvability of facets of the stress response. Due to prior studies suggesting a role of progesterone signaling in rotifer sex and dormancy, the membrane associated progesterone receptor is assayed as a candidate gene that could show positive selection indicating rapid divergence. Despite some sequence variation that may contribute to functional differences among species, results indicate this hormone receptor is under purifying selection. Detailed analyses of multiple stress responses and their evolution as performed here will be imperative to understanding current patterns of local adaptation and trait-environment correlations. Such research also is key to predicting persistence of species upon introduction to novel habitats and exposure to new stressors (e.g., warming due to climate change). Perhaps one of the most intriguing results of this dissertation is the rapid, adaptive change in levels of sex and dormancy in a metazoan through new mutations or re-arrangements of the genetic material. This suggests species may be able to rapidly evolve tolerance of new stressors, even if standing genetic variation does not currently encompass the suite of alleles necessary for survival.

Master of Science / School of Family Studies and Human Services / Jared Durtschi / Much of the literature in sexuality and aging focuses on the physical aspects of the sexual relationship such as dysfunction and decline in frequency. In doing so, aging is viewed in a negative light because of its implied connection to dull sexuality and poor sexual satisfaction. However, despite potential age related sexual changes, many couples remain happy later in life in their relationships. Using data from 3,005 adults over the age of 57 from the National Social Life, Health and Aging Project data, we tested hypotheses using three different age groups: Newly Old (57-64), Young-Old (65-74), and Old (75-85). The results indicated that across each age group physical pleasure was linked with relationship happiness and emotional satisfaction. However, sexual frequency was not linked with relationship happiness or emotional satisfaction. In several cases, emotional accessibility moderated—served as a protective factor—in the associations between the nature of the sexual relationship and the nature of the quality of the romantic relationship. Clinical implications include identifying a clinically modifiable factor—emotional accessibility—that may mitigate the potential risk of changing sexuality to overall relationship happiness within older adult couples.