Factors influencing reproductive success of male sockeye salmon

Drew J. Hoysak
In this thesis I studied factors that influence reproductive success in two age classes of male sockeye salmon (Oncorhynchus nerka). In my first experiment I tested for the presence of frequency-dependent reproductive success of male age classes in single spawning events and examined the influence of the number of males present on frequency-dependence. I placed groups of males in an enclosure with a nesting female, allowed them to spawn, and determined paternity of the resulting offspring. In
more » ... ing offspring. In spawning trials with three males, frequency-dependent reproductive success was apparent. That is, both age classes had greater mean reproductive success when they were in the minority. However, frequency-dependent reproductive success was not present in groups with six males and the two age classes did not differ in mean reproductive success. My second study was a detailed examination of factors that may have influenced individual male reproductive success in the previous experiment. Alpha male positions were usually held by five-year-old (5Y) males characterized by large body size and large secondary sex traits. Among satellite males, three-year-old (3Y) males held positions closer to the female than did 5Y males, and distance from the female was a good predictor of whether or not a male would participate in spawning and of the order in which males began spawning. Overall, alpha males fertilized more eggs than did 3Y satellite males, and 3Y satellite males fertilized more than 5Y satellite males. Behaviour during spawning appeared to influence male success. Path analysis suggested that male success was directly affected by the time spent in spawning posture which, in turn, was influenced by the time that a male began to spawn. I found no evidence of a relationship between male fertilization success and distance from the female during spawning. In the next experiment, I compared male age classes in their success in sperm competition. I fertilized eggs in vitro with mixtures of milt from pairs of mal [...]
doi:10.14288/1.0090552 fatcat:gerfxywoinh6xln3ey6sps3b7m