Date of Award


Publication Type

Master Thesis

Degree Name



Biological Sciences

First Advisor

Pitcher, Trevor




Chinook salmon (Oncorhynchus tshawytscha) exhibit male alternative reproductive tactics (ARTs), in which males are either large, dominant hooknoses, or small precocious jacks. Multiple mating (or polyandry) is common by females, which partly explains the intense sperm competition. I examined whether females benefit genetically by mating with multiple males thus promoting sperm competition and whether males can use seminal plasma to influence the potential outcome during sperm competition. I found that polyandrous females do indeed benefit genetically compared to monandrous (singly mated) females through an increase in offspring hatching success. The benefits received by polyandrous females varied significantly depending on the ARTs used during sperm competition trials, with crosses involving a jack and a hooknose producing the offspring with the highest hatching success. I also found that jack seminal plasma decreases hooknose sperm velocity, with potential implications on the outcome of sperm competition between the two tactics.