We are studying species in the genus Orconectes, including O. rusticus (rusty crayfish), O. sanbornii (Sanborn's crayfish), and O. obscurus (Allegheny crayfish). These species inhabit adjacent, non-overlapping ranges that span Ohio, Pennsylvania and West Virginia. During the Wisconsinian glaciation, about 20 thousand years ago, the distributions of these species were forced south into glacial refugia. Upon the recession of the glacier, each species migrated north as the climate warmed and the modern watershed was established, eventually filling their current distributions.
More recently, the rusty crayfish has become an invasive species in many parts of the northeastern and midwestern United States (and also north into Canada), perhaps spread by its use as bait. In Wisconsin the rusty crayfish has eliminated native crayfish species from some habitats. We are studying the mechanisms of invasion of the rusty crayfish in Ohio, which may include out-competing the native species for shelter and other resources and hybridization with the native species.
|Here two crayfish compete for shelter in an aquarium. Success in competition for shelter may result in faster growth and eventually greater fitness (number of offspring).|
|Crayfish attach fertilized eggs to their abdomens where they develop and eventually hatch into miniature adults. This feature allows us to sample DNA of females and offspring to perform paternity analysis|
This project is an extension of my doctoral work on spontaneous mutation in plants. As the ultimate source of genetic variation, spontaneous mutation is an essential part of evolution. However, many aspects of mutation, such as the rate and average size of phenotypic effect, are not well understood.
Individual mutations usually have very small phenotypic effects, decrease fitness, and may occur anywhere in the genome making it difficult to study spontaneous mutation. In order to increase the visibility of mutational effects, researchers perform mutation accumulation (MA) experiments in which they allow mutations that would normally be removed by natural selection (because most are harmful to an organismÕs fitness) to remain in the genome and be passed on to offspring who may have new mutations of their own. After several generations (10 or more), each MA genotype (or line) has multiple mutations and the combined effects on the phenotype (number of seeds, fruits or flowers produced) may be detectable.
Recall that phenotype is derived from genotype and that to achieve that final phenotype the organism must translate the genotype into phenotype through gene expression. Thus, mutations which affect a phenotype like number of fruits must also affect gene expression during plant development.
Using whole-genome microarrays with three MA lines displaying divergent fitness relative to the un-mutated Ancestor, kindly provided by Ruth Shaw at the University of Minnesota, I measured gene expression for all 29,000+ genes of Arabidopsis thaliana (a small annual plant of the Mustard family, Brassicaceae). From that data, I have identified a smaller list of several hundred genes that may display differential expression in a MA line relative to the expression of that same gene in the Ancestor.
Chase Nelson (Honors Project 2010) confirmed differential expression for several of the candidate genes using RT-PCR, including chromomethyltransferase3 (CMT3), a gene important in the maintenance of methylation patterns in the Arabidopsis genome.
Marta Robertson (Honors Project 2011) designed a study of the epigenetic profile and phenotype of the CMT3 mutant line relative to the ancestral Col-0 genotype. In addition, Marta's experimental design included the effect of nutrient level on epigenetic patterns in additional A. thaliana genotypes known to differ in their sensitivity to nutrient availability. Marta planned to assay the epigenetic phenotype using AFLP genotyping with restriction enzymes that recognize the same restriction site (isoschizomers) but are differentially sensitive to methylation. However, we are currently facing technical difficulties with the MS-AFLP.