Genetic diversity and propagule pressure: determinants of invasion success?

Ongoing invasions by non-indigenous species (NIS) have fundamentally modified aquatic communities in Canada and abroad. The process of biological invasion encompasses a series of stages and embedded barriers, which NIS must pass through from donor to recipient regions. Establishment of NIS and their attendant impacts call for detailed studies on factors influencing invasion success, including the role of genetics. Introduced populations may experience genetic bottleneck during invasion, hence propagule pressure and associated genetic diversity are relevant considerations. High propagule pressure may enhance genetic diversity by representing a larger pool of propagules from donor region, and mitigates the effect of demographic stochasticity. Moreover, high genetic diversity allows for rapid response to changing environments. My goal in this dissertation was to characterize genetic diversity of aquatic NIS in successfully established and pre-introduced populations. Exploring the invasion genetics of the comb jelly Mnemiopsis leidyi (chapters two and three), I identified two separate pathways from North America to two regions of Europe, with hub-and-spoke dispersal from each initial colonization site. Then, I explored vector activity along possible invasion pathways of golden mussel Limnoperna fortunei in Asia and South America. My findings (chapter four) demonstrated that more diverse introduced populations of L. fortunei likely received higher propagule pressure than less diverse ones, indicating correspondence between genetic diversity and vector activity. The level of genetic diversity in introduced populations was at same, or higher, relative to native populations (chapters two to four). Furthermore, I explored the development of a genetic bottleneck prior to an introduction event using Ion Torrent technology to sequence small subunit ribosomal DNA fragments (chapter five) in zooplankton community resident in ballast water of an operating vessel. The number of Operational Taxonomic Units decreased throughout trans-Atlantic voyages, indicating developing genetic bottlenecks. Results provide empirical evidence for attenuation of genetic diversity prior to discharge of propagules, highlighting the role of pre-introduction phenomena in shaping genetic composition of introduced populations. This dissertation demonstrates the link between genetic diversity in source and recipient populations, and its relationship to vector activity. Future studies may clarify the relative roles of pre- versus post-introduction phenomena in influencing genetic composition of introduced populations