Thesis (Ph.D.) - University of St Andrews, August 2008.

Thesis (M.S.)--Marshall University, 2004. / Title from document title page. Document formatted into pages; contains viii, 72 p. including illustrations. Includes abstract. Includes bibliographical references (p. 33-37).

Thesis (Ph. D.)--Carleton University, 1988. / Also available in electronic format on the Internet.

Thesis (MSc)--University of Stellenbosch, 2005. / Bibliography. Also available via the Internet.

I examine some of the ecological and evolutionary implications of body size in hermit crabs, with special emphasis on the upper intertidal species Clibanarius digueti. In Chapter 1 I show that body size had a far greater effect than species identity on desiccation tolerance for shell-less individuals of C. digueti, Paguristes anahuacus, Pagurus lepidus, and Phimochirus roseus. In contrast with other intertidal taxa, there was no correlation between the upper tidal limit of a species and the expected desiccation tolerance of an average-sized, shell-less individual of that species. This suggests that the gastropod shell that normally houses the hermit crab is sufficient to eliminate desiccation as a community-structuring force in this guild. Clibanarius digueti exhibits strong sexual dimorphism in body size, with almost no overlap in size between adult males and females. In Chapter 2 I show that sexual differences in the intensity of selection on size favor this dimorphism. Specifically, male mating success depended more strongly on body size than did female fecundity. In fact, the rate of increase in fecundity with body size equalled the lowest previously recorded for decapod crustaceans, suggesting that sexual size dimorphism in this species may depend more on weak fecundity selection on females than on strong sexual selection on males. Documenting contemporary selection on a character, however, is not the same as documenting that selection caused the character to evolve. Chapter 3 presents the first empirical test in a single species (C. digueti) of the hypothesis that sexual size dimorphism represents an evolutionary response to sexual differences in selection on size. The test is based on a general model that predicts crab body size as a function of shell limitations, shell fit and body size. Both males and females occupied optimally sized shells of non-preferred species, but the greater the desirability of a shell species, the greater the tendency for males to occupy tighter-fitting shells than females. Males also apparently suffere higher mortality than similarly-sized females. According to the general model, these results agree with the hypothesis that differential selection is causally involved in the evolution of sexual size dimorphism, and contradict the alternative hypothesis that energetic constraints on females produce the dimorphism.

Estimating the sex of unknown human skeletal remains is important to the fields of forensic anthropology, bioarchaeology, and other specialties. I studied sexual dimorphism on the first and second ribs to estimate sex from skeletal remains. I employed two approaches. I used geometric morphometrics to analyze landmark and semilandmark coordinate points to examine the overall shape of the ribs. I also examined the sternal end of the ribs for size using the superior-inferior height (SIH) and anteriorposterior breadth (APB) in a binary logistic regression (BLR) model. Differences in male and female first and second ribs are undetectable when landmark coordinate points are used to capture shape variability, but significant differences in the shape of the ribs, however, are detected through the use of semilandmark coordinate points. Using semilandmark points to estimate sex presented an accuracy rate of 80.7% from the first rib, and 72.9% from the second rib. The use of the sternal end presents consistent results in its ability to estimate sex with an accuracy rate of 84.2%. The BLR model reveals significant differences between males and females than the geometric morphometric approach; it is more applicable for discerning sexual dimorphism of unknown individuals. This study reveals that while geometric morphometrics provides a powerful approach to assessing morphological differences, it is not always better than simpler methods, in this case, simple measurements analyzed through BLR. / Includes bibliography. / Thesis (M.A.)--Florida Atlantic University, 2018. / FAU Electronic Theses and Dissertations Collection

My dissertation focuses on the factors that influence variation in female reproductive success in plethodontid salamanders and in toads. Variation in reproductive success fuels evolutionary change. Although, females often have been overlooked in studies of reproductive success due to perceived lower levels of variation when compared to variation in male reproductive success, understanding factors influencing variation in female reproductive success is critical for several reasons. First, female reproduction is usually the limiting factor on population growth. Second, the factors affecting female reproduction provide the impetus for current and evolving patterns of sexual dimorphism. Lastly, male reproductive success inevitably is determined by the reproductive success of the females with which they mate. Recent theoretical developments of sexual conflict have contributed significantly to a renewed emphasis on studies of female reproductive success. Sexual conflict theory elucidates important factors, from the perspective of females, affecting female behavior and reproductive success. Sexual conflict assumes that a female will benefit, in terms of reproductive success and offspring viability, when she is able to freely choose among males, unconstrained by social and environmental factors. Female choice would be constrained if a non-preferred male (i.e., one that would be rejected by a freely choosing female) coerced a female to mate in order to increase his own mating success. The dynamics between discriminating females and non-preferred males will lead to a coevolutionary "arms race", referred to as sexual conflict. From this perspective, secondary male traits may not reflect their intrinsic quality, but rather their ability to manipulate or coerce female mating decisions. The current debate lies in the importance and pervasiveness of sexual conflict. To address the current view of sexual conflict, I investigated whether sexual conflict plays a role in the mating systems of amphibians. In particular, my results support the main assumption that females benefit from freely expressed female mate choice in toads. In addition, I explored the potential influence of sexual conflict in plethodontid salamanders. During mating trials, I documented novel female courtship behaviors. I also examined the effects of male courtship pheromones on female reproductive success to assess the potential role of male pheromones in sexual conflict. My results suggest that sexual conflict also may be an important factor in plethodontid mating systems. My investigations of sexual conflict theory have provided new insights and novel predictions for understanding sexual selection and sexual dimorphism. / Graduation date: 2005

Thesis (M. Sc.)--Carleton University, 1988. / Also available in electronic format on the Internet.

No description available.

We investigated possible sex differences in PRL secretory patterns and regulation by E$ sb2$ in gonadectomized Dorset x Leicester x Suffolk sheep kept under natural photoperiod (latitude 45$ sp circ 31 sp prime$). Patterns were assessed over 14 months in groups of 10 rams and ewes, half of which received E$ sb2$ replacement (Silastic implants) at the time of gonadectomy to maintain blood E$ sb2$ at ram breeding-season values. Mean monthly PRL level (based on two 3-h periods of blood sampling) was consistently elevated by E$ sb2$ in the ram (mean 19%), and during all but a few months in the spring and summer in the ewes (mean 90%). Sex differences in the mean PRL were most apparent for the E$ sb2$-treated sheep in August (rams 280 $ pm$ 54 ng/ml vs ewes 128 $ pm$ 18 ng/ml) and for the control sheep in November (rams 19 $ pm$ 5 ng/ml vs ewes 10 $ pm$ 2 ng/ml). Episodic PRL secretion (with 5-min sampling for 4 h) was assessed in every season. In all four groups, pulse amplitude and frequency and basal level were higher in summer than winter. E$ sb2$ treatment was associated with larger PRL pulses in both sexes in every season but summer, and with decreased (from 8.2 to 4.6 per 4 h) and increased (from 2.2 to 6.6 per 4 h) frequencies of pulses in rams in the spring and summer, respectively. The PRL response to TRH (two iv injections 50 ng/kg BW given 80 min apart) was also assessed in every season. Mean 40-min increases after injection were highest in spring and summer. E$ sb2$ treatment produced in both sexes a 2-3 fold larger increment 1 in every season, and increment 2 in specific seasons. Preinjection and increment values were positively correlated within animals of each group across seasons (r = 0.89 and 0.65). The Incr 2/lncr 1 ratio (mean 0.76 $ pm$ 0.10) was not affected by seasons or E$ sb2$, and did not denote a self priming effect of TRH. Diurnal patterns indicated that PRL mean levels during light and dark phases were not different from each other within