Acknowledgements:
We thank all the organisations and people that have assisted in the collection of samples. The Canadian Department of Fish and Wildlife and Fish and Wildlife Departments of Alaska and Oregon assisted us by providing information about sampling locations. In particular we thank Dr. Darcie Neffs of the Alaskan Department of Fish and Wildlife for collecting tubesnouts from Juneau (TuAK), Prof. Mike Bell for collecting the Alaskan threespine stickleback (TsAK) and Ms. Treasa Tufts who collected the ninespine sticklebacks. Dr. Sarah Smith-Wuitchik is thanked for her advice for sampling fish. We also thank Dr. Jon Mee and the members of the Rogers Lab at the University of Calgary who provided advice on finetuning the DNA extraction protocol. Finally, we would like to thank Ms. Hazel Cameron-Inglis for her assistance during a month and a half of field work. Funding for this work was provided by Alberta Innovates (20150252) and NSERC Discovery (RGPIN/03950-2017).