Demographic Factors and Male Behavioral Plasticity Affect Temporal Variation in Effective Breeding Number in Lake Sturgeon

Mating systems of polygamous fishes are dynamic and contribute to levels and apportionment of genetic diversity within and among populations and over time.  We used genetic parentage assignment to quantify the degree of intra- and inter-annual variation in reproductive success, mate number, and the effective number of breeding adults in lake sturgeon (Acipenser fulvescens) in a closed population in Black Lake, Michigan. Adults (N= 611 individuals captured 1,024 times) and larvae (N=3,566) were sampled during the entire spawning season in each of 7 consecutive years (2001-2007).  Reproductive success (RS) and mate number (MN) differed between sexes and varied greatly among individuals of each sex across years.  In all years, we observed a similar linear positive relationship between RS and MN for males and females.  Spawning time and location did not affect female RS or MN.  Male behavioral plasticity reflected in varying retention times at spawning sites affected male reproductive success. We estimated the effective number of breeding adults Nb using the linkage disequilibrium method (LD) for larval samples collected each year. Estimates of Nb were fairly constant as were breeding adult census sizes (N) among years (mean Nb ranged 63-126). Low inter-annual variation in Nb/N ratios (0.26 - 0.61) resulted from consistently low standardized variance of relative reproductive success across years even though the number of larvae collected, a surrogate measure of total annual larval production, varied 40-fold across years (437 – 16,417).