Current Research Projects
- Population genetics of local species of crayfish in the genus Orconectes.
- Spontaneous mutations affecting fitness in Arabidopsis thaliana.
- unPAK: Undergraduates Phenotyping Arabidopsis thaliana knockouts.
- Roles, AJ, M Rutter, I Dworkin, C Fenster, and J Conner. 2016. Field measurements of genotype by environment interaction for fitness caused by spontaneous mutations in Arabidopsis thaliana. Evolution 70:1039-1050.
- Kahrl, AF, RH Laushman, and AJ Roles. 2014. Evidence for multiple paternity in two species of Orconectes crayfish. Canadian Journal of Zoology 92:985-988.
- Zuber, ST, K Muller, RH Laushman, and AJ Roles. 2012. Hybridization between an invasive and a native species of the crayfish genus Orconectes in north-central Ohio. Journal of Crustacean Biology 39:962-971.
- Rutter, M, A Roles, J Conner, R Shaw, K Schneeberger, S Ossowski, D Weigel, and CB Fenster. 2012. Fitness of Arabidopsis thaliana mutation accumulation lines whose spontaneous mutations are known. Evolution 66:2335-2339.
- Roles, AJ and J Conner. 2008. Fitness effects of mutation accumulation in a natural outbred population of wild radish (Raphanus raphanistrum): Comparison of field and greenhouse environments. Evolution 62:1066-1075.
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, demonstrating 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 advanced. 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 '15) worked on assembling and annotating the mitochondrial genomes of O. rusticus and O. sanbornii. Full mitochondrial genome sequences are now available for a number of species of crayfish and we are doing comparative analysis with our taxa. We are also using these sequences to help us identify species-specific genetic markers that, in conjunction with nuclear markers, will be useful in estimating the rate of hybridization. James Medina ('15) and Jun Takaki ('17) have made important contributions to the latter effort.
- Elisa Henderson ('17) is planning to pursue an Honors Project studying patterns of genetic variation in these two species: (1) among native populations of each species and (2) at multiple sample sites along two invaded rivers (in which both species are observed). These invaded rivers are native for O. sanbornii but have recently been invaded by O. rusticus. Elisa is isolating DNA from our populations and will use RADSEQ to obtain genetic marker information. 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.
- Abby Bisesi ('17) is planning to pursue an Honors Project studying the structure of the mitochondrial genome in crayfishes. While the complement of coding regions in animal mtDNA is highly conserved, it appears that the regions encoding the initiation/termination of replication and transcription are more variable among groups of animals. Little is known about these important regulatory regions in crayfishes, which also exhibit an unusual degree of mitochondrial genome rearrangement. Abby will explore the use of models to study the structure of crayfish mitogenomes.
- 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 Emily Lumsdaine '14, James Medina '15, Clara Monsma '15, Emma Berg '18, and Jack Poyle '17). This study represents a new vein of research into spontaneous mutation, the topic of my graduate studies. We are 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. We are 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. We 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.
- 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.
The unPAK project is a multi-institutional collaboration focused on hands-on research experiences for undergraduates. We use a distributed research model in which groups at each participating institution follow a single set of procedures to phenotype Arabidopsis thaliana single-gene knockout mutants (SALK lines) for plant performance traits. There are thousands of SALK T-DNA lines with little or no information on plant phenotype currently available. In our standard experiments, we plant seeds from 11 phytometers (control genotypes) and 122 single-insert mutant genotypes, following the common protocols. In addition, institutions pursue individual projects exploring the effects of other factors on mutant phenotypes. Examples include studies of the impact of increased soil salinity or nutrient stress.
- Somatic mutation and selection (with Emma Bergh '18 and Jack Poyle '17). See description above for the spontaneous mutation project. In this experiment, we have chosen SALK T-DNA lines with insertions in genes known to be involved in DNA repair, as well as a few randomly chosen SALK lines, and select phytometers. We will apply a UVB exposure treatment (exposed or not exposed) early during the life cycle and examine the performance of seeds from early fruits versus those from late fruits.
- Epigenetic effects of heat stress (with Emma Bergh '18, Jack Poyle '17, and the Samis lab at University of Prince Edward Island). In summer 2015, we had an unPAK experiment that experienced an unexpected heat stress, just as plants were beginning to bolt. We continued the experiment -- the plants did not die and did set fruit, though output was relatively low. We then discovered that another unPAK participant, the Samis lab at UPEI, also experienced an unexpected heat stress, though very early in the life cycle. Both my lab and the Samis lab kept seeds from these unexpected heat stress experiments and we have 10 SALK lines that were grown in both experiments. We are now planning to study whether an unexpected heat stress experienced by parents has consequences for the performance of their offspring.
Updated August 2016
- Summer 2015: My lab's first foray into unPAK included an unplanned heat stress just as the plants were beginning to bolt! Jun Takaki ('17), Karsten Jurkiewicz ('17), and Nia Daids ('19) contributed to our planting two replicated sets of 122 mutants each (plus the 11 phytometers).
- Fall 2015: We repeated the experiment from Summer 2015 under benign control conditions (NO heat stress) with one of the sets of 122 mutants. However, the soil batch appeared to have low nutrients and our plants were stunted in growth. Jun Takaki ('17) assisted with planting and phenotyping during growth in the fall. Emma Bergh ('18) completed all of the harvest phenotyping in spring 2016.
- Summer 2016: We grew the second set of mutants from summer 2015 under benign control conditions (NO heat stress); this time our soil was VERY good and our plants were huge! Emma Bergh ('18) and Jack Poyle ('17) carried out this experiment, with an occasional hand from Elisa Henderson ('17).
by Angela Roles