Date of Award


Document Type

Campus Access Dissertation


Biological Sciences

First Advisor

Thomas J Hilbish


The effects of invasive species on native communities are of major concern worldwide. These species can have grave ecological, economical, and genetic impacts on the communities in which they invade. Through hybridization, invasive species also threaten the genetic integrity of the native species by means of genetic pollution. In the marine environment, the Mediterranean mussel Mytilus galloprovincialis is a highly invasive species that has successfully invaded a number of geographic locations. This species has been shown to ecologically affect communities by outcompeting and displacing native species in both South Africa and California. Studies examining the genetic impacts M. galloprovincialis has on native species have been focused in the northeast Pacific Ocean. In the North Pacific, M. galloprovincialis has been repeatedly introduced to several locations within the native range of M. trossulus. These introductions have resulted in at least three separate geographic locations where the two species are now sympatric, providing a naturally occurring experiment to explore the ecological and genetic impacts an invasive has on native species. Previous studies have extensively studied the geographic distribution and the hybrid zone characteristics of these two species within the northeastern Pacific region. The northwestern Pacific region, however, has not been as closely examined. The purpose of this research project is to determine the geographic distribution of M. galloprovincialis, M. trossulus, and their hybrids in northern Japan. From this research I describe the extent of the hybrid zone(s) between these species, as well as reporting the levels of hybridization and introgression occurring in this region. I found two separate hybrid zones along the northern and southern Hokkaido coast, each with their own genetic structure. Extensive hybridization (many populations above 50%) is occurs along the southern Hokkaido coast, while the northern hybrid zone is characterized by low levels of hybridization (less than 20%). The southern hybrid zone exhibits an unprecedented level of hybridization, while the level of hybridization in the northern hybrid zone is more consistent to those observed in the northeastern Pacific region. Even with the drastic difference in levels of hybridization occurring between the two hybrid zones in Hokkaido, hybrids in both locations are restricted to the F1 generation and introgression is low or non-existent. I document that hybrid sterility is at least one of the factors contributing to the low levels of introgression observed in Hokkaido. Currently it is unknown whether hybrid infertility is a characteristic of the hybrid zones found in the northeastern Pacific. Furthermore, the research conducted for this dissertation has also reported an overall mis-regulation of mitochondrial inheritance in the individuals around the island of Hokkaido. The mis-regulation observed in this region is novel in the sense it is not associated with hybridization as previous studies have found. In addition, the mis-regulation observed highly skewed by gender, with females having significantly greater mis-regulation in comparison to males. The research presented in this dissertation provides vital information to begin to examine the question of the consistency of the genetic impact M. galloprovincialis has on M. trossulus by its invasion.