Adult reproductive behavior plays an important role in population growth and genetic structuring, which is less well understood at the individual level for long-lived fish species like lake sturgeon (Acipenser fulvescens). Using genetic determination of parentage, I examined the effects of adult spawning behavior and environmental factors on the species' mating system, genetic structure within a population and on offspring survival and timing to dispersal at the individual level. Analyses were based on adults and larvae captured during 7 years (2001-2007) in the Upper Black River, Black Lake, Michigan. First, I quantified the degree of temporal variation in aspects of the lake sturgeon mating system. The species is polygamous, where males and females mate with a large number of individuals. Mate number and reproductive success (RS, the number of larvae) varied between sexes. However, the linear positive relationship between RS and mate number was similar in males and females. Female RS and mate number was independent of body size though RS and mate number for males slightly increased with increasing body size. Females spawning at different times during the season and locations did not differ in RS or mate number. Mating pairs between males and females that arrived at spawning areas >8 days apart accounted for 30% of total mating pairs averaged across years, suggesting that temporally discrete spawning groups identified based on direct observations were not reproductively isolated. Second, I tested for evidence of genetic differentiation among groups of adults spawning at different times in the season over 9 years (2001-2009). Although significant genetic differences were observed between early and late groups of adults captured during > 2 years, evidence of isolation by time was lacking based on low variance in allele frequency (FST) between early and late spawning groups and lack of correlation between pairwise relatedness and pairwise differences in spawning time. Third, I estimated effective population size (Ne), effective number of breeders (Nb) and degrees to which inter-annual variation in Nb was correlated with adult demographic characteristics. Estimates of Nb and adult census sizes were fairly constant among years. The Nb/N ratios varied 0.26 - 0.61 among years, consistent with low standardized variance (variance/(mean)2) in RS across years. Ne per generation (132, 95% CI: 104-167) was close to the estimates of annual Nb (harmonic mean: 88). Fourth, I evaluated the relative importance of environmental factors (water temperature and discharge) and maternal effects (female body size, location and timing of spawning) on the embryonic and larval developmental time until dispersal (ELDTUD). Both environmental variables and maternal effects of female and spawning time were equally important predictors of ELDTUD. Finally, I evaluated differences in relative larval loss among females when larvae dispersed a short distance (from two sites 0.15 and 1.5 km from spawning areas) during two consecutive nights. Larval collections were composed of unequal proportions of offspring from females but there was no significant difference in relative larval loss among females. Overall, the study greatly improves understanding of adult reproductive ecology, the roles of adult spawning behavior and environmental factors on timing to dispersal and survival of lake sturgeon at critical early life stages.
Read
