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Description
Speciation is the fundamental process that has generated the vast diversity of life on earth. The hallmark of speciation is the evolution of barriers to gene flow. These barriers may reduce gene flow either by keeping incipient species from hybridizing at all (pre-zygotic), or by reducing the fitness of hybrids (post-zygotic). To understand the genetic architecture of these barriers and how they evolve, I studied a genus of wasps that exhibits barriers to gene flow that act both pre- and post-zygotically. Nasonia is a genus of four species of parasitoid wasps that can be hybridized in the laboratory. When two of these species, N. vitripennis and N. giraulti are mated, their offspring suffer, depending on the generation and cross examined, up to 80% mortality during larval development due to incompatible genic interactions between their nuclear and mitochondrial genomes. These species also exhibit pre-zygotic isolation, meaning they are more likely to mate with their own species when given the choice. I examined these two species and their hybrids to determine the genetic and physiological bases of both speciation mechanisms and to understand the evolutionary forces leading to them. I present results that indicate that the oxidative phosphorylation (OXPHOS) pathway, an essential pathway that is responsible for mitochondrial energy generation, is impaired in hybrids of these two species. These results indicate that this impairment is due to the unique evolutionary dynamics of the combined nuclear and mitochondrial origin of this pathway. I also present results showing that, as larvae, these hybrids experience retarded growth linked to the previously observed mortality and I explore possible physiological mechanisms for this. Finally, I show that the pre-mating isolation is due to a change in a single pheromone component in N. vitripennis males, that this change is under simple genetic control, and that it evolved neutrally before being co-opted as a species recognition signal. These results are an important addition to our overall understanding of the mechanisms of speciation and showcase Nasonia as an emerging model for the study of the genetics of speciation.
ContributorsGibson, Joshua D (Author) / Gadau, Jürgen (Thesis advisor) / Harrison, Jon (Committee member) / Pratt, Stephen (Committee member) / Verrelli, Brian (Committee member) / Willis, Wayne (Committee member) / Arizona State University (Publisher)
Created2013
Description
Forensic entomology is the use of insects in legal investigations, and relies heavily upon calculating the time of colonization (TOC) of insects on remains using temperature-dependent growth rates. If a body is exposed to temperatures that exceed an insect’s critical limit, TOC calculations could be severely affected. The determination of critical thermal limits of forensically-relevant insects is crucial, as their presence or absence could alter the overall postmortem interval (PMI) calculation. This study focuses on the larvae of Phormia regina (Meigen) (Diptera: Calliphoridae), a forensically relevant blow fly common across North America. Three populations were examined (Arizona, Colorado, and New Jersey), and five day old larvae were exposed to one of two temperatures, 39℃ or 45℃, for five hours. Across all colonies, the survival rate was lower at 45℃ than 39℃, in both larval and emerged adult stages. The Arizona colony experienced a harsher drop in survival rates at 45℃ than either the Colorado or New Jersey colonies. This research suggests that the range of 39℃ - 45℃ approaches the critical thermal limit for P. regina, but does not yet exhibit a near or complete failure of survivorship that a critical temperature would cause at this duration of time. However, there is opportunity for further studies to examine this critical temperature by investigating other temperatures within the 39℃ - 45℃ range and at longer durations of time in these temperatures.
ContributorsMcNeil, Tara (Author) / Weidner, Lauren (Thesis director) / Meeds, Andrew (Committee member) / Barrett, The Honors College (Contributor) / School of Humanities, Arts, and Cultural Studies (Contributor) / School of Mathematical and Natural Sciences (Contributor)
Created2022-05