Assortative Mating in a Genetic Colour Polymorphic Population of Chinook Salmon

Carotenoids are responsible for the characteristic red flesh, skin and egg pigmentation of salmonids. In nature, some Chinook salmon (Oncorhynchus tshawytscha) populations exhibit extreme variation in carotenoid utilization, with white-fleshed races co-existing with red-fleshed races, and variants existing across the spectrum. Red and white Chinook salmon differ due to genetic polymorphisms that affect carotenoid metabolism and deposition. Carotenoids are important for sexual selection in salmon; however, white Chinook salmon lack carotenoid spawning colouration. Despite this, white Chinook salmon individuals continue to persist in mixed and pure phenotype populations. In colour polymorphic species, mating dynamics can favor the maintenance of genetic variation through assortative mating for colour. Using spawning channels, we explored the possibility of colour-assortative mating in red and white Chinook salmon from the Quesnel River, British Columbia. We determined offspring parentage using microsatellite genetic markers to infer mate choice. To further determine if mating behaviour was responsible for the persistence of the two phenotypes, genetic divergence (F_ST) was measured between red and white adults in the population. The maintenance of white Chinook salmon in nature is puzzling, however, the results of our study provide insight into how this genetic polymorphism is maintained in a population.

Keywords: mate choice, salmon