Current Research Projects
- Population genetics of local species of crayfish in the genus Orconectes.
- Spontaneous mutations affecting fitness in Arabidopsis thaliana.
Detailed project descriptions
My research on the population genetics of crayfish species began with the work described in Kahrl et al. (2014), performing paternity analysis in two species. Our success in this first exploration into the mating systems of crayfish allowed us to pursue further work, demon- strating hybridization between an invasive species and a local species - an uncommon event in crayfishes.
Though hybridization is generally considered rare, we have reason to believe that the recent biogeographic history of these taxa increases the likelihood of hybridization among close relatives. We are interested in the effects of range contraction and expansion on the integrity of species boundaries and the distribution of genetic variation within and among species. The Central Highlands of the U.S. (which includes Ohio) were recently glaciated; thus, the crayfish living here now must have been displaced south when the glaciers ad- vanced. During that time, close relatives may have been in contact and able to interbreed. These taxa would have expanded north again when the glaciers receded (about 13,000 years ago) but due to recent history, may have retained the capacity for gene flow - should they meet again. Thus, when the invasive species arrived in local rivers, hybridization is possible.
The immediate trajectory of this project is two-pronged: 1) identifying factors contributing to the ability of these species to hybridize and 2) evaluating the current and potential future consequences of continued hybridization.
- Recent graduates (Dyani Sabin '14 and Laura Gray '14) worked on assembling and annotating the mitochondrial genomes of O. rusticus and O. sanbornii. We will use these sequences to help us identify species-specific markers that, in conjunction with nuclear markers, will be useful in estimating the rate of hybridization. The lab is also collaborating with colleagues at the University of Malaysia to generate mitogenome sequences for other North American crayfish genera in order to study the evolution of mitogenome structure.
- Many students have contributed to our studies of morphological and genetic variation withn and among populations of O. rusticus and O. sanbornii. We have sampled several native populations of each species as well as two rivers that are native for O. sanbornii but have been invaded by O. rusticus. We will use this data to examine the extent and effects of hybridization between these taxa as well as elucidate the recent biogeography of these taxa.
- Stephen Williams (Honors Project 2012) examined the distribution of genetic variation within and between populations of the rusty crayfish in both it's native and invasive ranges. He also asked how the presence of the rusty crayfish may impact the genetic variation in the native Sanborn's crayfish by comparing allopatric and sympatric populations of these species.
- Connor Bacon ('13) and Jonathan Levin ('12) studied the morphological variation within and between Sanborn's crayfish and the rusty crayfish. We collected samples from allopatric native populations of each species, which Connor and Jonathan measured for a large number of morphological traits commonly known to vary in crayfish.
- Sunjana Supekar (Honors Project 2011) studied the effects of a common herbicide, metolachlor, on the behavior of the invasive rusty crayfish, the native Sanborn's crayfish, and the interaction between the two species.
- Sierra Zuber (Honors Project 2011) and Katherine Muller (Honors Project 2010) used nuclear and mitochondrial molecular markers to study hybridization between the invasive rusty crayfish and the native Sanborn's crayfish in a local river.
- Liz Baird (Honors Project 2009) studied competition for shelter between the invasive rusty crayfish and the native Allegheny crayfish.
|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). |
- Ariel Kahrl (Honors Project 2009) used microsatellite markers to discover that Sanborn's crayfish and the Allegheny crayfish both exhibit multiple paternity with an average of two sires per brood.
|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 |
- Erica Borg (Honors Project 2008) used microsatellite markers to study the correlation between genetic diversity and water quality for each of these three crayfish species.
My second research trajectory follows from my graduate work, seeking greater understanding of the ultimate source of new genetic variation: spontaneous mutation. Mutation is both a creative and destructive force in evolution as a new mutation may either improve an individual's survival and reproduction or reduce it. In addition to being the raw material of evolution, studies of spontaneous mutation have the potential to improve our understanding of human health and disease, particularly with respect to the dynamics of cancer (which is frequently caused by new spontaneous mutations arising within an individual).
In graduate school, my work began to explore the effect of environmental conditions on the effects of spontaneous mutations for fitness in plants. My work (with colleagues) demonstrated that mutational effects are often conditional (Rutter et al. 2012, Roles and Conner 2008), in contrast to work carried out in the laboratory. We also corroborated an interesting result first found in the lab: in our study system (Arabidopsis thaliana), up to half of new mutations may be beneficial for plant fitness rather than harmful! This result remains unexplained and is the subject of my current work - I am testing the hypothesis that somatic selection may bias the observed distribution of mutational effects on fitness.
- The effects of somatic mutation on the observed distribution of mutational effects on fitness in Arabidopsis thaliana (with E. Lumsdaine '14, J. Medina '15, and C. Monsma '15). This study represents a new vein of research into spontaneous mutation, the topic of my graduate studies. I am testing the hypothesis that selection on somatic mutations is shifting the observed distribution of mutational effects in Arabidopsis thaliana, favoring beneficial mutations and weeding out harmful ones. I am planning to mutagenize young plants to create a hetergeneous population of meristematic cells, which will then experience selection during somatic growth, before the initiation of reproductive growth. I will compare the fitness distributions of seeds that experienced differing amounts of somatic selection to determine whether this process may bias the observed distribution of mutational effects.
Updated February 2015
- 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.
- Chase Nelson (Honors Project 2010) followed up on work from my doctorate in which I measured gene expression for MA lines of Arabidopsis thaliana, identifying several hundred genes that may display differential expression in a MA line relative to the expression of that same gene in the Ancestor. Chase 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.
by Angela Roles