Sylvester, Terrence Pradakshana (2022-12). Broad-Scale Structural Evolution in Invertebrate Genomes and the Population Genomics of Jewel Scarabs in the Southwestern US. Doctoral Dissertation.
Thesis
Genome structure, at a fundamental level, can be described by the division of the genome into a discrete number of chromosomes and further divided into autosomes and sex chromosomes. An array of mechanisms or selection pressures can lead to changes in both of these genome characteristics. Meiotic drive, segregation mechanisms, sexual antagonism, epistasis, benefits of higher or lower recombination, and drift have all been invoked to explain changes in the number of chromosomes and the proportion of the genome that is sex-linked through sex chromosomes. Despite over a century of work, this level of genome organization has been resistant to broad generalizations that can explain the striking variation we observe among species. I use comparative phylogenetic approaches to determine the degree to which rates of chromosome number and sex chromosome system evolution vary among orders of insects. I also use these approaches to infer whether mutations that have led to divergence in chromosome number are deleterious, neutral, or beneficial. The second part of my dissertation is focused on population genomics. As climate changes, many species develop discontinuous distributions. When a species is separated into many isolated demes, the risk of local extirpation increases. Chrysina gloriosa is a jewel scarab restricted to high elevations in west Texas, southern New Mexico, southern Arizona, and northern Mexico, where it feeds on several species of trees in the genus Juniperus. This beetle is highly sought after by collectors and is one of the most charismatic insects in North America. Despite this, there is currently no population genetic data that would allow for estimates of the health or resiliency of populations. Using population genomic data, I determine the degree of gene flow among populations of the scarab jewel beetle C. gloriosa across the southwestern United States and determine the landscape characteristics that best predict the isolation of demes.
