Shifts in Zygosity and Allele Frequencies over the First Year of Life in Yellow Perch

The first year of life represents a period of high mortality in most fishes, often typified by highly selective mortality on size, growth rates, or other genotypic or phenotypic factors.  However, the direction and trends of selection on genotypes in fish populations during the first year of life remain uncertain.  Selection could increase average genome-wide heterozygosity in populations via benefits to more genetically diverse individuals (i.e., heterozygosity-fitness correlations).  Alternatively, selection may increase or decrease the frequency of advantageous or deleterious alleles, or random mortality could result in little change.  We examined these hypotheses by stocking adult yellow perch into two ponds, allowing them to spawn naturally, and subsampling the offspring throughout the first year of life (August, late October, and the following April).  All individuals were genotyped at 10 microsatellite loci to determine whether levels of heterozygosity or allele frequencies significantly differed between offspring and adults, and whether they shifted over time in offspring. We examined potential heterozygosity-fitness correlations in each pond by correlating heterozygosity to individual size.  Our results could elucidate the importance of selective mortality during early life in fish and allow us to postulate how selection during early life may alter the genetic structure of later generations.