The inherent asymmetry of female meiosis presents an opportunity for genetic material to gain an evolutionary advantage during the formation of the egg. Since centromeres mediate chromosomal segregation by forming the bridge between microtubules and chromosomes during cell division, they are loci that can drive, or selfishly evolve, during female meiosis by manipulating the process of entering the egg. Mimulus guttatus, a species of yellow monkeyflowers, has the best documented case of centromeric drive (Fishman and Saunders, 2008). Since homozygotes for drive have decreased pollen viability, lower seed counts, and poor reproductive success, CENH3 —the gene that encodes the H3 histone specific to centromeres— has evolved to suppress centromeric drive. CENH3 is duplicated in Mimulus, and the sequence variation of CENH3_A suggests that this paralog can suppress centromeric drive during female meiosis (Finseth et al. 2015). Our analysis of gene expression levels in meiotic and mitotic tissues indicates that both CENH3_A and CENH3_B are still expressed at similar levels, suggesting that the paralogs have not specialized for different roles in cell divisions. However, qPCR was only performed with nine tissue samples, so further analysis of gene expression with a larger sample set is needed to confirm whether or not the CENH3 paralogs have specialized roles in meiosis and mitosis.

Pollinator-mediated competition and facilitation are two important mechanisms mediating co-flowering community assembly. Experimental studies, however, have mostly focused on evaluating outcomes for a single interacting partner at a single location. Studies that evaluate spatial variation in the bidirectional effects between co-flowering species are necessary if we aim to advance our understanding of the processes that mediate species coexistence in diverse co-flowering communities. Here, we examine geographic variation (i.e. at landscape level) in bidirectional pollinator-mediated effects between co-flowering and We evaluated effects on pollen transfer dynamics (conspecific and heterospecific pollen deposition) and plant reproductive success. We found evidence of asymmetrical effects (one species is disrupted and the other one is facilitated) but the effects were highly dependent on geographical location. Furthermore, effects on pollen transfer dynamics did not always translate to effects on overall plant reproductive success (i.e. pollen tube growth) highlighting the importance of evaluating effects at multiple stages of the pollination process. Overall, our results provide evidence of a spatial mosaic of pollinator-mediated interactions between co-flowering species and suggest that community assembly processes could result from competition and facilitation acting simultaneously. Our study highlights the importance of experimental studies that evaluate the prevalence of competitive and facilitative interactions in the field, and that expand across a wide geographical context, in order to more fully understand the mechanisms that shape plant communities in nature.

The flexible shell of some oviparous reptiles has led to differences in nutrient mobilization and water relations when compared to their rigid-shelled counterparts. Flexible-shelled eggs gain more water during development, and because of the shell structure, yolk calcium content is higher than that of eggshells. When water availability is altered for reptiles with flexible-shelled eggs, differences in both energy and nutrient utilization are observed. This study was designed to determine the baseline metabolic rate during development for the snake, Pantherophis guttatus under normal conditions, and to observe how changes in eggshell calcium and water availability impact embryonic oxygen consumption. Eggshell calcium was decreased while water uptake was increased by removing the outer calcareous eggshell layer from some eggs. When eggs are left intact, an exponential increase in oxygen consumption is observed, supporting previous studies, while removal of the eggshell produces no effect on metabolism.

Invasive species, a top threat affecting global biodiversity, become invasive through a process including four stages: transport, establishment, spread, impact and integration. Species currently in this process provide opportunities to empirically derive the mechanisms driving each of these stages, make predictions based on these mechanisms and then to test these predictions. This research examines the current invaded distribution, potential invasion and community-level impacts of a popular aquarium trade fish (Hemichromis guttatus Günther, 1862) in an endemic hotspot, Cuatro Ciénegas, in Coahuila, México and discusses the policy and conservation management implications of these findings. In Chapter 1, the problem of invasive species, the study site and the focal species of this work are introduced. In Chapter 2, the critical thermal minimum and maximum temperature limits and temperature preference of H. guttatus are identified because temperature is hypothesized to be an important factor controlling this fish’s distribution. The results indicate that H. guttatus has a wide temperature tolerance range (a characteristic of a ‘good’ invader), that preference is a more informative metric for predicting invasion than absolute tolerances, and that resource-poor environments may promote searching behaviors that cause an invasive fish to increase its range. In Chapter 3, the results of a field survey are analyzed and temperature, pH, depth and the presence of vegetation are all found to be related to H. guttatus presence. Invasion risk of several as-of-yet uninvaded sites in Cuatro Ciénegas is assessed. In Chapter 4, competitive and predatory interactions of H. guttatus on an endemic, threatened cichlid (Herichthys minckleyi) and a macroinvertebrate community respectively are investigated. The results suggest that while H. guttatus does not directly impact H. minckleyi through competition in these conditions, it may inhibit reproduction and alter H. minckleyi’s behavior through aggressive interactions. In Chapter 5, all results are synthesized and a determination of the invasive status of H. guttatus in Cuatro Ciénegas is made. The results presented here will be useful in identifying areas with a high risk of invasion by this popular ornamental fish, thus allowing the implementation of policy and management actions to prevent or at least ameliorate the impacts of an invasion and will add to the growing knowledge of how invasive species affect native systems. / text

<p>The problem is two fold: how does natural selection operate on systems of interacting genes and how does natural selection operate in natural populations. To address the first problem, I have conducted a theoretical investigation into the evolution of control and the distribution of mutations in a simple system of interacting genes, a linear metabolic pathway. I found that control is distributed unevenly between enzymes, with upstream enzymes possessing the greatest control and accumulating the most beneficial mutations during adaptive evolution. To address the second problem, I investigated the evolution of copper tolerance in the common yellow monkeyflower, Mimulus guttatus. I genetically mapped a major locus controlling copper tolerance, Tol1. A Dobzhansky-Muller incompatibility was hypothesized to also be controlled by Tol1, however, we have demonstrated that it maps to another, tightly linked locus, Nec1. Finally, we investigated the parallel evolution of copper tolerance in multiple new discovered mine populations. We found that copper tolerance has evolved in parallel multiple times via at least two distinct physiological mechanisms. In four mine populations, there was a strong signal of selection at markers linked to Tol1, implying that copper tolerance has evolved via the same genetic mechanisms in these populations.</p> / Dissertation

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The oceans are essential for humanity, yet these systems continue to be degraded and suffer from pollution, habitat destruction and overexploitation. The Costa Rican Gulf of Nicoya is a productive gulf that is fished by both large-scale industrial fisheries and small-scale artisanal fishermen. However, the gulf is profoundly overfished and there has been a shift in both the type of species and size of fishes being targeted, which has had devastating economic and ecological effects in the region. To improve their livelihoods, artisanal fishermen have together with governmental agencies instituted partially protected marine protected areas, known as AMPRs which are intended to give artisanal fishermen exclusive fishing rights and to better the health of the ecosystems. However, these AMPRs can vary greatly within and between each other in aspects such as what types of fishing gear is allowed. To investigate how fishing techniques impact the health of the fish stocks and the wellbeing of fishermen within an AMPR, the size of a target fish, Spotted Rose Snapper (Lutjanus guttatus) and the number of undesired fish caught, was compared based on the number of approved fishing methods such as nets, longlines and commercial scuba diving, between different zones. This was conducted by identifying and measuring catch in collaboration with the National University of Costa Rica, who contributed with databases and field assistance, and artisanal dead bait longline fishermen (bottom long line) in the Paquera-Tambor AMPR. The results showed that in areas where fishing gear is more restricted, the mean weight of Spotted Rose Snapper was higher, but the relative proportion bycatch was not different. Furthermore, there was no difference in legal capture or breeding lengths between areas with high and low restriction of fishing gear. This indicates that the effects of overfishing are less predominant in zones where fewer fishing methods are permitted. The restriction of fishing methods could increase biodiversity and size in fish by exploiting less cohorts of populations. The preservation of size in fish species is very important regarding reproductive success, and it is therefore paramount that larger individuals are protected. This could be accomplished by for example, restricting the amount of allowed fishing gear or introducing maximum catch sizes. However, an improvement of the fish stocks, and therefore human wellbeing cannot be achieved in the Gulf of Nicoya without a revision of the strategies of two influential governmental bodies, the Costa Rican coast guard and the Costa Rican Institute of Fisheries and Aquaculture.