MS, University of Cincinnati, 2023, Arts and Sciences: Biological Sciences

The Darwin-Bateman paradigm theorizes that males maximize their reproductive success by mating indiscriminately and often, while females benefit by investing in the selection of a smaller number of high-quality males. However, there is increasing recognition that sexual selection occurs on both male and female traits, even within species, and that sex roles operate dynamically on a continuum influenced by numerous factors. Even so, much variation in the strength and direction of sexual selection remains unexplained. This study examines variation in sex roles across the animal kingdom by conducting a synthesis on existing sexual selection research where we model the relative strength of sexual selection between sexes using generally-available predictors including potential reproductive rates and mating systems. The results demonstrate that (1) the commonly-invoked potential reproductive rate is important in modeling sex differences in the Bateman gradient and opportunity for sexual selection, while the importance of sex ratios appears in this study to be eclipsed by other variables, and (2) sex-role models are significantly more robust when interactions between variables are accounted for. We conclude that sex roles are highly context-dependent and should be modeled according to a mix of population and life-history characteristics.

Committee: Stephen Matter Ph.D. (Committee Chair); Michal Polak Ph.D. (Committee Member); Nathan Morehouse Ph.D. (Committee Member) Subjects: Biology

MS, Kent State University, 2013, College of Arts and Sciences / Department of Biological Sciences

Male katydids produce mating calls through stridulation to attract potential mates. Calls were recorded in the field and analyzed to compare between two related species that occur in overlapping ranges in the northwestern United States. Distinct differences were found between the two species' calls in both dominant frequency and chirp rate. Also, one species interspersed trills amongst the chirps of the call, while the other species' call did not include trills. These distinct call differences can be used for species identification and can be easier to differentiate than physical characteristics. The upper limits of sexual selection can be estimated using upper limits on Bateman gradients, which represent how fecundity increases with additional mates. Upper limits on Bateman gradients are expected to be constrained by various factors such as nutrition. These upper limits were estimated using controlled mating experiments with katydids on high and low protein diets (as adults) by measuring how maximum fecundity (fecundity with ideal mates) increased with each mating. Decreases in both maximum fecundity and the potential for sexual selection were expected in males and females due to protein limitation. This would result from decreased potential fecundity in low protein females and decreased value of nuptial gifts given by low protein males. The results did not support our predictions as strongly as hoped, but a decrease in the upper limits of sexual selection was nearly significant in low protein males, evidenced by reduced fecundity gains from remating. Also, spermatophores (the katydid nuptial gift) had a more complicated effect on fecundity than expected. Spermatophore size differed between males' first and second matings, however, larger spermatophores did not always confer more value to females, particularly in second matings. Stable isotope analysis was used to examine the lack of significant effects from differences in dietary protein on th (open full item for complete abstract)

Committee: Patrick Lorch (Advisor); Mark Kershner (Committee Member); Sean Veney (Committee Member) Subjects: Animal Sciences; Animals; Behavioral Sciences; Behaviorial Sciences; Biology; Ecology; Entomology; Evolution and Development; Organismal Biology; Zoology