Research

My current research interests run in two directions: genetics work with Honors Genetics students working on the Georgia Tech Urban Honey Bee Project with Jennifer Leavey and Scholarship of Teaching and Learning centered around the efficacy of open education resources.

My research has focused on the ecological and genetic factors that promote and maintain biological diversity. At the University of Toronto, I worked with Aneil Agrawal to gather empirical evidence that mutation rates vary according to condition in eukaryotes. I also collaborated on a year-long project to determine how condition influences the magnitude of epistasis (genetic interactions).

At the University of British Columbia, I asked what factors generate and maintain diversity using Escherichia coli experimental evolution. I examined the maintenance of diversity by assessing the degree to which seasonal resource availability maintains pairs of diversified E. coli ecotypes (Spencer et al 2007 Evol. Ecol. Res.). Second, I collaborated with lab technician Melanie Bertrand to identify and quantify expression level differences between these pairs of ecotypes in a key metabolism gene (Spencer et al 2008 PLoS Genetics). Further work on microarrays has revealed a more complete understanding of expression differences between the ecotypes (Le Gac et al 2008 Genetics). To assess the propensity of a population to diversify at various points in its evolutionary history, I delved into the frozen “fossil record” of a diversified E. coli population to determine with what probability history replays itself. I have also collaborated with other members of the lab group on an empirical demonstration of character displacement (Spencer et al 2008 PNAS).

At the University of Georgia, I studied how genetic interactions (epistasis) impact aging. Using classical fruit fly genetics techniques, I assessed the impacts of foreign mutations in wild type genetic backgrounds. My data show that the genetic background in which a gene is expressed can dramatically alter the phenotype of fitness traits such as lifespan and mortality rate. Specifically, I have found that ‘aging genes’ (single genes that extend longevity in fruit flies and other model organisms) vary in their ability to increase life expectancy (Spencer et al 2003 Aging Cell). This variation depends upon the sex and the genetic background of the flies that express the ‘aging genes’.

I also looked at several standard visible marker mutations in Drosophila to determine if they have fitness effects when expressed in different genetic backgrounds or strains. Again, I found a strong effect of genetic background in flies expressing these putatively neutral markers (Spencer and Promislow 2005 J. Heredity). My research indicates the dramatic effects that genetic background can have on fitness traits. These experiments also showcase a critical concern in studies of evolutionary and molecular genetics: Geneticists often seek out genes of major effect for fitness traits or complex syndromes such as human disease. My research shows that when genes of major effect are expressed in individuals with different genotypes, they do not always produce a consistent phenotype.

Working with Paul Leberg at the University of Louisiana at Lafayette, I evaluated the utility of microsatellites for detecting severe demographic bottlenecks. To do this, we compared the amount of genetic diversity lost in bottlenecks of different sizes. We used the western mosquitofish, (Gambusia affinis Poeciliidae) as our study organism and created forced bottlenecks of varying sizes in large cattle tanks in an open field. After microsatellite allele frequency analysis, we compared our results to Paul’s earlier allozyme work in a similar system and made the following conclusions about the utility of allozymes versus microsatellites in bottleneck analysis. While allozymes can detect the presence or absence of a recent population bottleneck, small numbers of highly polymorphic loci (such as microsatellites) can not only detect a population’s recent history of demographic bottlenecks but can also be used to estimate of the magnitude of the bottlenecks’ severity (Spencer and Leberg 2000 Mol. Ecol.).

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