INVESTIGATIONS INTO LAKE STURGEON REPRODUCTIVE EFFORT : TRADE-OFFS BETWEEN CURRENT AND FUTURE REPRODUCTION
Organisms often vary resource expenditures devoted to reproduction in response to environmental conditions and to biotic conspecific and heterospecific interactions. Resource allocation decisions can also affect future reproductive effort and success. This thesis investigated how variability in behavioral, biological, and environmental factors was associated with measures of current and future reproductive effort. Additionally, I investigated how ovarian fluid affected egg fertilization rate and survival during embryogenesis, and how measures of sperm quality were affected by ovarian fluid. Analyses in this study were conducted on an intensely studied lake sturgeon population from Black Lake, MI. Lake sturgeon are a threatened species throughout the Great Lakes region. The species’ longevity and iteroparous spawning behavior, along with long-term nature of our study made lake sturgeon an excellent candidate to study inter-annual reproductive outcomes. In Chapter 1, I examined how intra- and inter-sexual behavior, biotic variables, and environmental conditions affected individual investments in current year reproductive effort. Potential implications for inter-spawning interval and life-time reproductive success generally are also discussed. I quantified year-to-year variability in morphology and duration of the lake sturgeon spawning period. Results indicated that male lake sturgeon inter-spawning interval decreased as body size (a surrogate of age) increased. For female lake sturgeon, inter-spawning interval was not associated with spawning behavior, body size, or environmental variability. For male lake sturgeon, findings suggest that current reproductive effort and variability in spawning behavior is likely influenced by environmental variability, while investment in reproductive opportunities increased with age. In Chapter 2, I examined the role of ovarian fluid in lake sturgeon egg fertilization success and post-fertilization embryo survival when eggs are fertilized with sperm from related and unrelated males. Experiments documented the effect of ovarian fluid on sperm quality and velocity. Eggs fertilized by males not related to a female showed higher proportional egg survival than half-sibling males 72-hours following fertilization. No interaction of the unrinsed ovarian fluid and relatedness was observed, suggesting that higher egg survival associated with unrelated males was not attributed to ovarian fluid. The lack of interaction implied that ovarian fluid is not likely a pre-zygotic mechanism to reduce the likelihood of consanguineous matings. The lack of rinsing of ovarian fluid during sperm activation resulted in reduction of sperm velocity and motility, but results were unaffected by the relatedness of the mated pair. Results demonstrated that ovarian fluid may alter sperm velocity and quality, but the reduction in survival of progeny from half-sibling matings did not result from ovarian fluid on the egg surface. Collectively, findings presented provide greater understanding of how behavioral, biological, and environmental factors affect reproduction in lake sturgeon. Studies highlight the value of long-term collection of data to inform species management. Results generated from these experiments contribute to the understanding of how long-lived species plastically respond to current environmental conditions and how effort toward reproductive success varies with age and size at the individual and to population levels.Read
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Electronic Theses & Dissertations
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- Material Type
Larson, Jr., Douglas L.
- Thesis Advisors
Scribner, Kim T.
- Program of Study
Fisheries and Wildlife - Master of Science
- Degree Level
- 101 pages