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Thesis (Ph. D.)--Carleton University, 1997. / Also available in electronic format on the Internet.

Selfish genetic elements break the rules of Mendelian inheritance to bias their transmission to following generations, often with negative fitness consequences. A striking example involves selfish X chromosomes that operate in males and interfere with the production of sperm that carry a Y chromosome. Only X chromosome-bearing sperm are produced, and this can result in extraordinary female-biased sex-ratio distortions. Most studies have focused on how selfish X chromosomes operate in and affect males, and there has been relatively little work on their consequences in females. In this thesis, I characterize fitness effects and transmission in females, in a recently discovered selfish X chromosome system in Drosophila testacea, a common woodland fly. I show that females with two copies of the selfish X chromosome have reduced fitness compared to females carrying zero, or one copy. Specifically, these females have a lower hatch rate and lifetime fecundity. Additionally, I show that heterozygous females are more likely to transmit the selfish X chromosome than the wildtype copy to their offspring. I observe this transmission bias in eggs, larvae, and adults, which suggests that the selfish X chromosome is preferentially segregating into the egg, rather than the polar bodies, during oogenesis. We believe this is the first documented case of a selfish X chromosome acting through both sexes. The negative fitness effects and the biased transmission in males and females will have important consequences on the evolutionary dynamics of the selfish X chromosome. In addition, the phenomenon of biased transmission in both sexes has the potential to yield interesting insights in the mechanism of meiotic drive. / Graduate / 2022-05-12

Drosophila melanogaster has been integral to unravelling the mechanisms of animalian immunity. Diverse species of Drosophila with sequenced genomes have been used to characterize how immune systems respond to natural selection. However, Drosophila is an incredibly speciose lineage, especially so in the subgenus Drosophila. Of the 12 genomes sequenced in 2007, ushering in the era of Drosophila comparative genomics, only three were subgenus Drosophila flies, and none were from the lesser- characterized Immigrans-Tripunctata clade. Recently, multiple Immigrans-Tripunctata clade Drosophila have been sequenced, including the transcriptome of Drosophila neotestacea. I investigated the realized immune responses of D. neotestacea to characterize the immune repertoire of this divergent lineage. The signalling pathways of D. neotestacea were largely conserved, though there were interesting patterns of evolution in antimicrobial peptide genes (AMPs). One of these AMPs, a diptericin, was highly dissimilar to diptericins in D. melanogaster, and conserved in other subgenus Drosophila flies. This prompted me to characterize the evolution of the diptericin gene family in Drosophila. I found that Drosophila diptericins have evolved under positive selection, and display intriguing differences in net charge to well-conserved diptericin domains. I assessed the expression profile of this divergent D. neotestacea diptericin, and found that it did not respond to Serratia bacterial challenge, unlike diptericin in D. melanogaster. I also highlight a potential novel drosocin-like AMP conserved throughout the subgenus Drosophila. These results agree that signalling pathways are highly conserved in diverse insects, including Drosophila. However seemingly-conserved effectors of the Drosophila immune response (such as AMPs) may have previously unappreciated variation in expression and function. / Graduate / 0718 / 0353 / 0369 / markhans@uvic.ca