Temporal trends in genetic diversity within a northern pike population and estimates of effective population size, based on microsatellite DNA data

I developed an approach to examining temporal trends in genetic variation within fish populations and applied it to the northern pike (Esox lucius) population of Lake Escanaba, Wisconsin. First, fifteen microsatellite DNA markers were developed. Genetic variation at these microsatellite loci was assessed using the polymerase chain reaction, which allowed for the use of unpreserved fish scales as a source of DNA. Samples from collections of scales originally taken in 1961, 1977, and 1993 showed polymorphisms in seven (47%) of the 15 microsatellite loci. I resolved higher levels of genetic variation than previously reported for northern pike.; Effective population size (N{dollar}sb{lcub}rm e{rcub}{dollar}), an indicator of the rate of loss of neutral genetic variation within a population, was estimated from temporal changes in allele frequencies at the seven polymorphic loci. Use of a historical fish scale collection made it possible to: (1) increase the precision of estimates by increasing the time interval between samples, and (2) use an equation developed for discrete generations without correcting for demographic parameters. Estimates of N{dollar}sb{lcub}rm e{rcub}{dollar} for the time intervals 1961-77 and 1977-93 were 35 and 72, respectively. For the entire interval, 1961-93, the estimate of N{dollar}sb{lcub}e{rcub}{dollar} was 48 when based on the weighted harmonic mean of the above two estimates or 125 when calculated from 1961 and 1993 samples only. An N{dollar}sb{lcub}e{rcub}{dollar} of 48 over a 32-year period would imply that this population lost as much as 8% of its heterozygosity in that time.; A second method of estimating N{dollar}sb{lcub}rm e{rcub}{dollar}, based on gametic disequlibrium, was applied to the molecular data. Estimates for 1961, 1977, and 1993 were 8, 124, and 33, respectively. Ratios of N{dollar}sb{lcub}rm e{rcub}{dollar} to census size (N) were similar for both methods of estimation; they ranged from 0.01 to 0.14 and averaged only 0.07.; Results suggest the feasibility of using genetic methods based on microsatellite loci data to compare historical trends in N{dollar}sb{lcub}rm e{rcub}{dollar} with population dynamic parameters (e.g., population size, survival and reproductive rates). Such comparisons will help to evaluate the relationship between genetic diversity and long-term persistence and productivity of natural populations.