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Open Access Publications from the University of California

Scholarly Works (4 results)

  • Article
  • Peer Reviewed
UC Irvine Previously Published Works (2015)
Environments that vary within a generation of an organism provide opportunities for adaptation if the level of variation is severe and predictable. We describe a model of evolution in such environments with genotypes that show trade-offs in viability and fecundity. One genotype develops rapidly and has superior viability but reduced fertility relative to the alternative genotype. Conditions that allow the evolution of the rapidly developing genotypes are explored. We show how the evolution of ovoviviparity and resource specialization in Drosophila sechellia shares many important features of this model. We suggest that our model may capture many of the evolutionary forces responsible for the evolution of niche specialization and ovoviviparity seen in D. sechellia.
    Cover page: The Evolution of Ovoviviparity in a Temporally Varying Environment.Creative Commons 'BY' version 4.0 license
    • Thesis
    • Peer Reviewed
    UC Irvine Electronic Theses and Dissertations (2020)

    This dissertation focused on two central theories in experimental evolution; studying the death spiral and looking at trade-offs in adapted populations to a toxin in their environment. These results are summarized in Chapter 1. Chapter 2 focused on quantifying the efficacy of ingested dyes (using the ‘Smurf’ assay) to predict when an individual would die. This can be extremely useful for many research problems in aging. The death spiral is a short period prior to death that is marked by a dramatic decline in physiological health. The results show three key conclusions: that all blue dyes used had significant negative effects on mean longevity, only a small fraction of the flies showed the Smurf phenotype prior to death, and among the small fraction that did become Smurfs most (40-60%) become blue during their last 24 hours of life. The research in Chapters 3-5 focused on the phenotypic and genomic evolution of urea adapted populations. Insects are often exposed to many toxic substances in their environments. Urea and ammonia differ from most studies of resistance to toxic pesticides because of their wide-ranging effects on organismal and cellular physiology. The UX and UTB selection groups (adapted to high levels of urea in the larval stage of development), displayed slower larval feeding rates, slower larval growth rates, and lower starvation resistance compared to the other populations reared that had not adapted to urea. The UX and UTB selection regimes also showed higher viability, faster development time, and lower starvation resistance when reared on food supplemented with urea compared to controls. Chapter 4 of this dissertation studied genomic differentiation among populations subjected to different types of selection for tolerance to urea in their larval food. The RUX, reverse selected of the urea adapted populations still maintained measurable levels of adaptation to urea suggesting any reverse selection is slow. We saw parallel evolution occurring in the replicates of the same environmental populations, as well as genomic differentiation in the urea adapted lines, UX, UTB and RUX versus the control population of AUC. The starting conditions for the important gene regions might have been important and very different for the UX and UTB populations. These differences may account for why these populations share only 50% of the same significantly differentiated SNPS (single nucleotide polymorphisms). Chapter 5 sought to connect potential genes as the causative agents for specific phenotypes studied in Chapter 3. FLAM, the fused lasso additive model, is a statistical learning tool for determining which genes may affect differentiated phenotypes. The FLAM analysis provided us with 53 SNPS that had large effects on the four phenotypes studied – larval feeding rate, larval growth rate, development time and viability. Almost 500 genes were located to be potentially responsible for the 53 SNPS identified by FLAM.

      Cover page: The Genomics of Experimental Evolution
      • Article
      • Peer Reviewed
      UC Irvine Previously Published Works (2021)
      A collection of forty populations were used to study the phenotypic adaptation of Drosophila melanogaster larvae to urea-laced food. A long-term goal of this research is to map genes responsible for these phenotypes. This mapping requires large numbers of populations. Thus, we studied fifteen populations subjected to direct selection for urea tolerance and five controls. In addition, we studied another twenty populations which had not been exposed to urea but were subjected to stress or demographic selection. In this study, we describe the differentiation in these population for six phenotypes: (1) larval feeding rates, (2) larval viability in urea-laced food, (3) larval development time in urea-laced food, (4) adult starvation times, (5) adult desiccation times, and (6) larval growth rates. No significant differences were observed for desiccation resistance. The demographically/stress-selected populations had longer times to starvation than urea-selected populations. The urea-adapted populations showed elevated survival and reduced development time in urea-laced food relative to the control and nonadapted populations. The urea-adapted populations also showed reduced larval feeding rates relative to controls. We show that there is a strong linear relationship between feeding rates and growth rates at the same larval ages feeding rates were measured. This suggests that feeding rates are correlated with food intake and growth. This relationship between larval feeding rates, food consumption, and efficiency has been postulated to involve important trade-offs that govern larval evolution in stressful environments. Our results support the idea that energy allocation is a central organizing theme in adaptive evolution.
        Cover page: The effects of adaptation to urea on feeding rates and growth in Drosophila larvae
        • Article
        • Peer Reviewed
        UC Irvine Previously Published Works (2020)
        The ability to predict when an individual will die can be extremely useful for many research problems in aging. A technique for predicting death in the model organism, Drosophila melanogaster, has been proposed which relies on an increase in the permeability of the fly intestinal system, allowing dyes from the diet to permeate the body of the fly shortly before death. In this study we sought to verify this claim in a large cohort study using different populations of D. melanogaster and different dyes. We found that only about 50% of the individuals showed a visible distribution of dye before death. This number did not vary substantially with the dye used. Most flies that did turn a blue color before death did so within 24 hours of death. There was also a measurable effect of the dye on the fly mean longevity. These results would tend to limit the utility of this method depending on the application the method was intended for.
          Cover page: Predicting death by the loss of intestinal function
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