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 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 males that
differed in age. The milt mixtures contained equal numbers of sperm from each male.
Paternity analysis of the resulting offspring revealed that success in sperm competition
did not depend on male age. However, success in these competitive fertilizations did
not conform to the fair raffle model of sperm competition. Paternity in most of the egg
batches was biased in favour of one male. I did not detect any morphological or genetic
correlates of success in sperm competition.
In my final set of experiments I used in vitro fertilization to examine some aspects
of sockeye salmon fertilization dynamics. Sperm maintained high fertility for 10 s after
being exposed to water but fertility dropped sharply after that. The association
between eggs and sperm occurs very rapidly. 80% fertilization success was achieved
with five s of sperm-egg mixing and c. 25% success was achieved with < 0.5 s of
sperm-egg mixing. Sperm from 3Y and 5Y males differed little in motility and did not
differ at all in their propensity to fertilize eggs.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:BVAU.2429/13112 |
| Date | 05 1900 |
| Creators | Hoysak, Drew J. |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Relation | UBC Retrospective Theses Digitization Project [http://www.library.ubc.ca/archives/retro_theses/] |
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