Freeland, Joanna R

The recent northward expansion of the white-footed mouse (Peromyscus leucopus) in response to climatic changes provides a natural experiment to explore potential adaptive genetic variation within the clock gene Per1 in Peromyscus undergoing latitudinal shifts, as well as, the possibility of hybridization and introgression related to novel secondary contact with its sister species the deer mouse (Peromyscus maniculatus). Because clock genes influence the timing of behaviors critical for survival, variations in genotype may reflect an organism's ability to persist in different environments. Hybridization followed by introgression may increase the adaptive potential of a species by quickly generating adaptive variation through novel genetic recombination or by the transfer of species-specific alleles that have evolved in response to certain environments. In chapter 2, I used microsatellite and mtDNA markers to test for hybridization and introgression between P. maniculatus and P. leucopus and found that interbreeding is occurring at a low frequency (<1%). In chapter 3, I tested for a latitudinal cline in a polyglycine repeat located within the Per1 gene of Peromyscus and discovered a putative cline in the Per1-142 and Per1-157 allele of P. leucopus and P. maniculatus, respectively. Chapter 4, further expands upon these findings, limitations, and the lack of evidence supporting introgression at the Per1 locus. Despite this lack of evidence, it is possible that novel hybridization has or could lead to adaptive introgression of other genes, allowing for the exchange of adaptive alleles or traits that could be advantageous for range expansion and adaption to future environmental changes.

Author Keywords: Clock genes, Hybridization, Latitudinal gradient, Per1, Peromyscus, Range Expansion

Magnolia acuminata (Cucumber tree) is the only native Magnolia in Canada, where it is both federally and provincially listed as endangered.Magnolia acuminata in Canada can be found inhabiting pockets of Carolinian forest within Norfolk and Niagara regions of southwestern Ontario. Using a combination of nuclear and chloroplast markers, this study assessed the genetic diversity and differentiation of M. acuminata in Canada, compared to samples from the core distribution of this species across the United States. Analyses revealed evidence of barriers to dispersal and gene flow among Ontario populations, although genetic diversity remains high and is in fact comparable to levels of diversity estimated across the much broader range of M. acuminata in the USA. When examining temporal differences in genetic diversity, our study found that seedlings were far fewer than mature trees in Ontario, and in one site in particular, diversity was lower in seedlings than that of the adult trees. This study raises concern regarding the future viability of M. acuminata in Ontario, and conservation managers should factor in the need to maintain genetic diversity in young trees for the long-term sustainability of M. acuminata in Ontario.

Author Keywords: conservation genetics, cpDNA, forest fragmentation, Magnolia acuminata, microsatellites, population genetic structure