**ABSTRACT NOT FOR CITATION WITHOUT AUTHOR PERMISSION. The title, authors, and abstract for this completion report are provided below. For a copy of the full completion report, please contact the author via e-mail at firstname.lastname@example.org. Questions? Contact the GLFC via email at email@example.com or via telephone at 734-662-3018.**
2 Univ. of Massachusetts, Amherst, MA 01003 USA
3 Wilfrid Laurier Univ., Waterloo, ON, N2L3C5 Canada
4 USGS, Conte Anadromous Fish Res Ctr, Turners Falls, MA 01376 USA
The life histories of anadromous and landlocked Sea Lamprey are similar, though landlocked populations lack exposure to seawater and thus experience relaxed selection on traits associated with survival in seawater including salinity tolerance and its underlying osmoregulatory mechanisms. This study investigated differences in survival, ion regulation in seawater and feeding of juvenile (fully metamorphosed) sea lamprey from anadromous and landlocked populations. Landlocked lamprey had lower survival in 35 ppt seawater compared to anadromous lamprey. Landlocked and anadromous populations showed strongly elevated gill NKA activity compared to ammocoetes, which also increased over time after exposure to 30 ppt seawater. Plasma ion concentrations after exposure to 30 ppt seawater were elevated in two upper Great Lakes populations compared to the anadromous population. These results suggest that there are small but detectable population-based differences in salinity performance that are consistent with recent, relaxed selection on traits for seawater entry in landlocked populations. Additionally, feeding behavior was assessed in landlocked and anadromous populations in freshwater and seawater in several two-week experiments. Landlocked lamprey showed greater attachments, increased number of feeders, and higher specific growth rate in freshwater compared to anadromous sea lamprey. This indicates that feeding in freshwater may be under positive selection for landlocked populations.