Demographic and genetic estimates of effective population size (Ne) reveals genetic compensation in steelhead trout

Estimates of effective population size (Ne) are required to predict the impacts of genetic drift and inbreeding on the evolutionary dynamics of populations. How the ratio of Ne to the number of sexually mature adults (N) varies in natural vertebrate populations has not been addressed. We examined the sensitivity of Ne/N to fluctuations of N and determined the major variables responsible for changing the ratio over a period of 17 years in a population of steelhead trout (Oncorhynchus mykiss) from Washington State. Demographic and genetic methods were used to estimate Ne. Genetic estimates of Ne were gained via temporal and linkage disequilibrium methods using data from eight microsatellite loci. DNA for genetic analysis was amplified from archived smolt scales. The Ne/N from 1977 to 1994, estimated using the temporal method, was 0.73 and the comprehensive demographic estimate of Ne/N over the same time period was 0.53. Demographic estimates of Ne indicated that variance in reproductive success had the most substantial impact on reducing Ne in this population, followed by fluctuations in population size. We found increased Ne/N ratios at low N, which we identified as genetic compensation. Combining the information from the demographic and genetic methods of estimating Ne allowed us to determine that a reduction in variance in reproductive success must be responsible for this compensation effect. Understanding genetic compensation in natural populations will be valuable for predicting the effects of changes in N (i.e. periods of high population density and bottlenecks) on the fitness and genetic variation of natural populations.     

Effective population size of steelhead trout: influence of variance in reproductive success, hatchery programs, and genetic compensation between life-history forms

The effective population size is influenced by many biological factors in natural populations. To evaluate their relative importance, we estimated the effective number of breeders per year (Nb) and effective population size per generation (Ne) in anadromous steelhead trout (Oncorhynchus mykiss) in the Hood River, Oregon (USA). Using demographic data and genetic parentage analysis on an almost complete sample of all adults that returned to the river over 15 years (>15,000 individuals), we estimated Nb for 13 run years and Ne for three entire generations. The results are as follows: (i) the ratio of Ne to the estimated census population size (N) was 0.17-0.40, with large variance in reproductive success among individuals being the primary cause of the reduction in Ne/N; (ii) fish from a traditional hatchery program (Htrad: nonlocal, multiple generations in a hatchery) had negative effects on Nb, not only by reducing mean reproductive success but also by increasing variance in reproductive success among breeding parents, whereas no sign of such effects was found in fish from supplementation hatchery programs (Hsupp: local, single generation in a hatchery); and (iii) Nb was relatively stable among run years, despite the widely fluctuating annual run sizes of anadromous adults. We found high levels of reproductive contribution of nonanadromous parents to anadromous offspring when anadromous run size is small, suggesting a genetic compensation between life-history forms (anadromous and nonanadromous). This is the first study showing that reproductive interaction between different life-history forms can buffer the genetic impact of fluctuating census size on Ne.     

Large variance in reproductive success and the Ne/N ratio

The ratio of the effective population size to adult (or census) population size (Ne/N) is an indicator of the extent of genetic variation expected in a population. It has been suggested that this ratio may be quite low for highly fecund species in which there is a sweepstakes-like chance of reproductive success, known as the Hedgecock effect. Here I show theoretically how the ratio may be quite small when there are only a few successful breeders (Nb) and that in this case, the Ne/N ratio is approximately Nb/N. In other words, high variance in reproductive success within a generation can result in a very low effective population size in an organism with large numbers of adults and consequently a very low Ne/N ratio. This finding appears robust when there is a large proportion of families with exactly two progeny or when there is random variation in progeny numbers among these families.     

The effects of cyclic dynamics and mating system on the effective size of an island mouflon population

The Haute Island mouflon (Ovis aries) population is isolated on one small (6.5 km2) island of the remote Kerguelen archipelago. Given a promiscuous mating system, a cyclic demography and a strong female-biased sex ratio after population crashes, we expected a low effective population size (Ne). We estimated Ne using demographic and temporal genetic approaches based on genetic information at 25 microsatellite loci from 62 and 58 mouflons sampled in 1988 and 2003, respectively. Genetic Ne estimates were higher than expected, varying between 104 and 250 depending on the methods used. Both demographic and genetic approaches show the Haute Island Ne is buffered against population crashes. The unexpectedly high Ne likely results from the cyclic winter crashes that allow young males to reproduce, limiting the variance of male reproductive success. Based on individual-based simulations, we suggest that despite a strongly female-biased sex ratio, the effects of the mating system on the effective population size more closely resemble random mating or weak polygyny.     

Sibship reconstruction demonstrates the extremely low effective population size of striped bass Morone saxatilis in the Santee–Cooper system, South Carolina, USA

For organisms with great fecundity and high mortality in early life stages, such as shellfish or fishes, the need to match reproductive activity with environmental conditions conducive to spawning, fertilization, larval development and recruitment may result in extreme variance in reproductive success among individuals. The main objective of this study was to investigate evidence of large variance in the reproductive success of the striped bass Morone saxatilis in the Santee–Cooper system, South Carolina, USA. Seven microsatellite loci were analysed in 603 recruits representing three yearly cohorts from 1992 to 1994, and a group analysis was performed to identify full-sib families. Large variance in reproductive success was detected, with a few large, full-sib families contributing disproportionately to each of the cohorts. The severity of sweepstakes reproductive success varied among cohorts depending on environmentally imposed mortality. Estimations of the effective number of breeders in these long-lived fish ranged from 24 in 1992 to 44 in 1994. Furthermore, the estimated genetic effective population size ( N _e = 93) is approximately four orders of magnitude lower than estimates of adult census size ( N  =   362 000). Furthermore, the presence of large full-sib families indicates that striped bass engage in pair mating in the wild. Heterogeneity in genetic composition was also observed among cohorts, suggesting that genetically different adults contribute to different cohorts and that chance rather than fitness variation determines reproductive success.     

Genetic effective size of a wild primate population: influence of current and historical demography

A comprehensive assessment of the determinants of effective population size (N(e)) requires estimates of variance in lifetime reproductive success and past changes in census numbers. For natural populations, such information can be best obtained by combining longitudinal data on individual life histories and genetic marker-based inferences of demographic history. Independent estimates of the variance effective size (N(ev), obtained from life-history data) and the inbreeding effective size (N((eI), obtained from genetic data) provide a means of disentangling the effects of current and historical demography. The purpose of this study was to assess the demographic determinants of N(e) in one of the most intensively studied natural populations of a vertebrate species: the population of savannah baboons (Papio cynocephalus) in the Amboseli Basin, southern Kenya. We tested the hypotheses that N(eV) < N < N(eI) (where N = population census number) due to a recent demographic bottleneck. N(eV) was estimated using a stochastic demographic model based on detailed life-history data spanning a 28-year period. Using empirical estimates of age-specific rates of survival and fertility for both sexes, individual-based simulations were used to estimate the variance in lifetime reproductive success. The resultant values translated into an N(eV)/N estimate of 0.329 (SD = 0.116, 95% CI = 0.172-0.537). Historical N(eI), was estimated from 14-locus microsatellite genotypes using a coalescent-based simulation model. Estimates of N(eI) were 2.2 to 7.2 times higher than the contemporary census number of the Amboseli baboon population. In addition to the effects of immigration, the disparity between historical N(eI) and contemporary N is likely attributable to the time lag between the recent drop in census numbers and the rate of increase in the average probability of allelic identity-by-descent. Thus, observed levels of genetic diversity may primarily reflect the population's prebottleneck history rather than its current demography.     

Temporal genetic stability and high effective population size despite fisheries-induced life-history trait evolution in the North Sea sole

Heavy fishing and other anthropogenic influences can have profound impact on a species' resilience to harvesting. Besides the decrease in the census and effective population size, strong declines in mature adults and recruiting individuals may lead to almost irreversible genetic changes in life-history traits. Here, we investigated the evolution of genetic diversity and effective population size in the heavily exploited sole (Solea solea), through the analysis of historical DNA from a collection of 1379 sole otoliths dating back from 1957. Despite documented shifts in life-history traits, neutral genetic diversity inferred from 11 microsatellite markers showed a remarkable stability over a period of 50 years of heavy fishing. Using simulations and corrections for fisheries induced demographic variation, both single-sample estimates and temporal estimates of effective population size (N(e) ) were always higher than 1000, suggesting that despite the severe census size decrease over a 50-year period of harvesting, genetic drift is probably not strong enough to significantly decrease the neutral diversity of this species in the North Sea. However, the inferred ratio of effective population size to the census size (N(e) /N(c) ) appears very small (10(-5) ), suggesting that overall only a low proportion of adults contribute to the next generation. The high N(e) level together with the low N(e) /N(c) ratio is probably caused by a combination of an equalized reproductive output of younger cohorts, a decrease in generation time and a large variance in reproductive success typical for marine species. Because strong evolutionary changes in age and size at first maturation have been observed for sole, changes in adaptive genetic variation should be further monitored to detect the evolutionary consequences of human-induced selection.     

Genetic consequences of polygyny and social structure in an Indian fruit bat, Cynopterus sphinx. II. Variance in male mating success and effective population size

Variance in reproductive success is a primary determinant of genetically effective population size (Ne), and thus has important implications for the role of genetic drift in the evolutionary dynamics of animal taxa characterized by polygynous mating systems. Here we report the results of a study designed to test the hypothesis that polygynous mating results in significantly reduced Ne in an age-structured population. This hypothesis was tested in a natural population of a harem-forming fruit bat, Cynopterus sphinx (Chiroptera: Pteropodidae), in western India. The influence of the mating system on the ratio of variance Ne to adult census number (N) was assessed using a mathematical model designed for age-structured populations that incorporated demographic and genetic data. Male mating success was assessed by means of direct and indirect paternity analysis using 10-locus microsatellite genotypes of adults and progeny from two consecutive breeding periods (n = 431 individually marked bats). Combined results from both analyses were used to infer the effective number of male parents in each breeding period. The relative proportion of successfully reproducing males and the size distribution of paternal sibships comprising each offspring cohort revealed an extremely high within-season variance in male mating success (up to 9.2 times higher than Poisson expectation). The resultant estimate of Ne/N for the C. sphinx study population was 0.42. As a result of polygynous mating, the predicted rate of drift (1/2Ne per generation) was 17.6% higher than expected from a Poisson distribution of male mating success. However, the estimated Ne/N was well within the 0.25-0.75 range expected for age-structured populations under normal demographic conditions. The life-history schedule of C. sphinx is characterized by a disproportionately short sexual maturation period scaled to adult life span. Consequently, the influence of polygynous mating on Ne/N is mitigated by the extensive overlap of generations. In C. sphinx, turnover of breeding males between seasons ensures a broader sampling of the adult male gamete pool than expected from the variance in mating success within a single breeding period.     

The effective size of annual plant populations: the interaction of a seed bank with fluctuating population size in maintaining genetic variation

Many annual plant populations undergo dramatic fluctuations in size. Such fluctuations can result in the loss of genetic variability. Here I formalize the potential for a seed bank to buffer against such genetic loss. The average time to seed germination (T) defines the generation time of "annuals" with a seed bank, and assuming random seed germination, I show that, under otherwise ideal conditions, a population's effective size (Ne) equals NT, where N is the number of adult plants. This result supports the general principle that lengthening the prereproductive period increases Ne. When adult numbers vary, Ne at any time depends on N and on the numbers contributing to the seed bank in previous seasons. Averaging these effects over time gives Ne approximately Nh + (T - 1)Na, where Nh and Na are the harmonic and arithmetic means of the adult population. Thus if T > 1, Ne is determined primarily by Na. Simulations showed that until fluctuations in N are large (>25x) this relationship is accurate. I extended the theory to incorporate a selfing rate (S) and reproductive variance (I) through seed production (k), outcrossed pollen (m), and variation in selfing rate: Ne = NT(1 -S/2)/(1 + I) = NT/[1 + FIS)(1 + I)]. Reproductive variance (I) equals [Ik(1 + S)2 + IM(1 - S)2 + 2(1 - S2)Ikm = S2IS(1 + Ik)]/4, , where Ij is the standardized variance (Vj/j2) of factor j and Ikm is the standardized covariance between k and m. These results are applicable to other organisms with a similar life history, such as freshwater crustaceans with diapausing eggs (e.g., tadpole shrimp, clam shrimp, and fairy shrimp) and other semelparous species with discrete breeding seasons and a variable maturation time (e.g., Pacific salmon).     

Impact of clonal growth on effective population size in Hymenoxys herbacea (Asteraceae)

By influencing the proliferation of different genotypes, clonal growth can affect the maintenance of genetic variability and magnitude of genetic drift within plant populations. However, estimates of effective population size rarely incorporate the contribution of both asexual and sexual reproduction. We estimated effective size (Ne) for two populations of the clonal, self-incompatible plant, Hymenoxys herbacea, using a stage-structured demographic model for organisms with asexual and sexual recruitment and then examined the impact of reproductive strategy using an elasticity analysis. Plant rosettes monitored in two successive years had high survival rates in both populations (mean 0.94). The mean number of sexually derived recruits per initial ramet was 0.041 (SE 0.039), whereas the mean number of clonal recruits was 0.61 (SE 0.90). Effective size was 1642 and 5769 in the two populations and the Ne/N ratio averaged 0.34, comparable to values for other clonal species. Elasticity analysis indicated that increases in both clonal and sexual recruitment cause an increase in Ne while increasing the variance reduced Ne. However, Ne was more sensitive to changes in the mean and variance of asexual recruitment than sexual recruitment. These results highlight the importance of considering asexual modes of reproduction when examining the role of genetic stochasticity in populations.     

Genetic effective size is three orders of magnitude smaller than adult census size in an abundant,Estuarine-dependent marine fish (Sciaenops ocellatus)

Using eight microsatellite loci and a variety of analytical methods, we estimated genetic effective size (N(e)) of an abundant and long-lived marine fish species, the red drum (Sciaenops ocellatus), in the northern Gulf of Mexico (Gulf). The ratio N(e)/N, where short-term variance N(e) was estimated via the temporal method from shifts in allele-frequency data over four cohorts and where N reflected a current estimate of adult census size in the northern Gulf, was approximately 0.001. In an idealized population, this ratio should approximate unity. The extraordinarily low value of N(e)/N appears to arise from high variance in individual reproductive success and perhaps more importantly from variance in productivity of critical spawning and nursery habitats located in spatially discrete bays and estuaries throughout the northern Gulf. An estimate of N(e) based on a coalescent approach, which measures long-term, inbreeding effective size, was four orders of magnitude lower than the estimate of current census size, suggesting that factors presently driving N(e)/N to low values among red drum in the northern Gulf may have operated similarly in the past. Models that predict N(e)/N exclusively from demographic and life-history features will seriously overestimate N(e) if variance in reproductive success and variance in productivity among spatially discrete demes is underestimated. Our results indicate that these variances, especially variance in productivity among demes, must be large for red drum. Moreover, our study indicates that vertebrate populations with enormous adult census numbers may still be at risk relative to decline and extinction from genetic factors.     

Temporal recruitment patterns and gene flow in kelp rockfish (Sebastes atrovirens)

Pelagic dispersal of marine organisms provides abundant opportunity for gene flow and presumably inhibits population genetic divergence. However, ephemeral, fine-scale, temporal and spatial genetic heterogeneity is frequently observed in settled propagules of marine species that otherwise exhibit broad-scale genetic homogeneity. A large variance in reproductive success is one explanation for this phenomenon. Here, genetic analyses of 16 microsatellite loci are used to examine temporal patterns of variation in young-of-year kelp rockfish (Sebastes atrovirens) recruiting to nearshore habitat in Monterey Bay, California, USA. Population structure of adults from central California is also evaluated to determine if spatial structure exists and might potentially contribute to recruitment patterns. Genetic homogeneity was found among 414 young-of-year sampled throughout the entire 1998 recruitment season. No substantial adult population structure was found among seven populations spanning 800 km of coastline that includes the Point Conception marine biogeographic boundary. Comparison of young-of-year and adult samples revealed no genetic differentiation and no measurable reduction in genetic variation of offspring, indicating little variance in reproductive success and no reduction in effective population size for this year class. Simulation analyses determined that the data set was sufficiently powerful to detect both slight population structure among adults and a small reduction in effective number of breeders contributing to this year class. The findings of high gene flow and low genetic drift have important implications for fisheries management and conservation efforts.     

Reproductive success and effective population size in woodrats (Neotoma macrotis)

Discrepancies between the census size and the genetically effective size of populations (N(e)) can be caused by a number of behavioural and demographic factors operating within populations. Specifically, strong skew in male reproductive success, as would be expected in a polygynous mating system, could cause a substantial decrease in N(e) relative to census size. Because the mating system of Neotoma macrotis had previously been described as one nearing harem polygyny, I examined the distribution of reproductive success and genetic variation within a population of this species. Combining genetic data and three years of field observations, I show that variance in reproductive success does not deviate from poisson expectations within either sex and variance in success is similar between the sexes. Furthermore, both males and females had multiple partners across litters in addition to some evidence of multiple paternity within litters. Despite a lack of strong skew in reproductive success, an estimate of N(e) based on a number of demographic parameters suggests that the ratio of N(e)/N in this population is 0.48. Although the ratio of N(e)/N suggests that the population is experiencing higher rates of genetic drift than would be expected based on census size alone, the population maintains high levels of genetic diversity. Estimates of neighbourhood size and patterns of recruitment to the study site suggest that immigration plays an important role in this population and may contribute to the maintenance of high levels of genetic diversity.     

Genetically dispersed effective population size determined by mitochondrial genes

A formula for variance effective population size (Ne) for analysis of mitochondrial genes is deduced and discussed. Only the female part of the population is taken into account; hence, Ne is, in the given case, the effective number of females. Ne = m2(N - 1)/sigma 2, where N is the number of females, sigma 2 is the variance of the reproductive contributions of individual females (measured as the number of their daughters that are part of the next generation), and m is the mean number of daughters per female.     

Effective number of breeding adults in Bufo bufo estimated from age-specific variation at minisatellite loci

Estimates of the effective number of breeding adults were derived for three semi-isolated populations of the common toad Bufo bufo based on temporal (i.e. adult-progeny) variance in allele frequency for three highly polymorphic minisatellite loci. Estimates of spatial variance in allele frequency among populations and of age-specific measures of genetic variability are also described. Each population was characterized by a low effective adult breeding number ( N _b) based on a large age-specific variance in mini-satellite allele frequency. Estimates of N _b (range 21–46 for population means across three loci) were ≊ 55–230-fold lower than estimates of total adult census size. The implications of low effective breeding numbers for long-term maintenance of genetic variability and population viability are discussed relative to the species' reproductive ecology, current land-use practices, and present and historical habitat modification and loss. The utility of indirect measures of population parameters such as N _b and N _e based on time-series data of minisatellite allele frequencies is discussed relative to similar measures estimated from commonly used genetic markers such as protein allozymes.     

Seed banks, salmon, and sleeping genes: effective population size in semelparous, age-structured species with fluctuating abundance

Previous studies reached contrasting conclusions regarding how fluctuations in abundance affect Ne in semelparous species with variable age at maturity: that Ne is determined by the arithmetic mean N among the T years within a generation (Ne approximately = T(N)t; monocarpic plants with seed banks) or the harmonic mean (Ne approximately T[symbol: see text]; Pacific salmon). I show that these conclusions arise from different model assumptions rather than inherent differences between the species. Sequentially applying standard, discrete-generation formulas for inbreeding Ne to a series of nominal generations accurately predicts the multigenerational rate of increase in inbreeding. Variability in mean realized reproductive success across years (kt) is the most important factor determining Ne and Ne/N. When abundance is driven by random variation in kt, Ne < or = T[symbol: see text] < T(N)t. With random variation in Nt and constant per capita seed production (C), variation in kt is low and Ne approximately T[symbol: see text]; however, if C varies among years, Ne can be closer to T[symbol: see text]. Because population regulation affects the genetic contribution of entire cohorts of monocarpic perennials, Ne for these species may be more closely approximated by T[symbol: see text] than by T(N)t. With density-dependent compensation, Cov(kt, Nt) < 0, and Ne is further reduced because relatively few breeders make a disproportionate contribution to the next generation.     

Determinants of effective population size for loci with different modes of inheritance

Here we report an assessment of the determinants of effective population size (N(e)) in species with overlapping generations. Specifically, we used a stochastic demographic model to investigate the influence of different life-history variables on N(e)/N (where N = population census number) and the influence of sex differences in life-history variables on N(e) for loci with different modes of inheritance. We applied an individual-based modeling approach to two datasets: one from a natural population of savannah baboons (Papio cynocephalus) in the Amboseli basin of southern Kenya and one from a human tribal population (the Gainj of Papua New Guinea). Simulation-based estimates of N(e)/N averaged 0.329 for the Amboseli baboon population (SD = 0.116, 95% CI = 0.172 - 0.537) and 0.786 for the Gainj (SD = 0.184, 95% CI = 0.498 - 1.115). Although variance in male fitness had a substantial impact on N(e)/N in each of the two primate populations, ratios of N(e) values for autosomal and sex-linked loci exhibited no significant departures from Poisson-expected values. In each case, similarities in sex-specific N(e) values were attributable to the unexpectedly high variance in female fitness. Variance in male fitness resulted primarily from age-dependent variance in reproductive success, whereas variance in female fitness resulted primarily from stochastic variance in survival during the reproductive phase.     

On the Potential for Estimating the Effective Number of Breeders from Heterozygote-Excess in Progeny

The important parameter of effective population size is rarely estimable directly from demographic data. Indirect estimates of effective population size may be made from genetic data such as temporal variation of allelic frequencies or linkage disequilibrium in cohorts. We suggest here that an indirect estimate of the effective number of breeders might be based on the excess of heterozygosity expected in a cohort of progeny produced by a limited number of males and females. In computer simulations, heterozygote excesses for 30 unlinked loci having various numbers of alleles and allele-frequency profiles were obtained for cohorts produced by samples of breeders drawn from an age-structured population and having known variance in reproductive success and effective number. The 95% confidence limits around the estimate contained the true effective population size in 70 of 72 trials and the Spearman rank correlation of estimated and actual values was 0.991. An estimate based on heterozygote excess might have certain advantages over the previous estimates, requiring only single-locus and single-cohort data, but the sampling error among individuals and the effect of departures from random union of gametes still need to be explored.     

Oceanographic drivers of offspring abundance may increase or decrease reproductive variance in a temperate marine fish

In species that reproduce into uncertain environments, the relationship between mean reproductive success (the abundance of new recruits) and the variance in reproductive success (whether adults contribute disproportionally more offspring) may not be straightforward because of stochastic environmental processes that create high variance in reproductive success among adults. In this study, we investigated the relationships between oceanography, reproductive success and reproductive variance in the black rockfish, Sebastes melanops, a long‐lived temperate reef fish with pelagic larvae. We quantified black rockfish recruitment, genetic diversity and growth rates from otolith microstructure over 5 years (2005–2009) during which oceanographic conditions differed. We used cross‐correlations to determine windows of time during which oceanographic variables were significantly correlated with the resulting abundance or genetic diversity of recruits. We found that warmer ocean temperatures were positively correlated with the abundance of recruits, as well as the effective number of breeders. In contrast, the strength of coastal upwelling during settlement was positively correlated with the annual abundance of new recruits, but was negatively correlated with the effective number of breeders. Larval growth rates were explained substantially more by temperature than by upwelling and suggested that temperature affected survival through growth, while upwelling affected survival through transport. Our results indicated that cold ocean temperatures and intense upwelling caused sweepstakes‐like processes to operate on black rockfish populations, despite high abundances of recruits. We propose that a decoupling of the mean and variance in reproductive success may be characteristic of organisms that reproduce into uncertain environments.     

Temporal effective size estimates of a managed walleye Sander vitreus population and implications for genetic-based management

The goal of this research was to use the long-term fishery data set and DNA from archived scales of walleye Sander vitreus in Escanaba Lake, WI, U.S.A., to improve the understanding of the underlying mechanism(s) influencing genetic diversity in naturally recruiting populations. The introduced population of S. vitreus in Escanaba Lake has a low mean effective population size ( N _E) between 124·6 and 185·5 despite a mean census size ( N _C) of 4659 ( N _E/ N _C c. 0·04), suggesting an accelerated rate of genetic drift between 1952 and 2002. These values are smaller than the median N _E range of several studies suggesting typical N _E/ N _C ratios of 0·11–0·16 in a wide range of taxa. N _E increased steadily during the past two sampled decades (1992 and 2002) and was consistent with a lowering of the variance in S. vitreus reproductive success, possibly linked to a large, sustained exploitation (mean 28%) rate. Variance in reproductive success is one of the most important factors influencing N _E in species, like S. vitreus , which have a potential for large fecundities and large juvenile mortalities (type III survivorship). The N _B estimates across six sequential cohorts (age classes of S. vitreus , assayed from 1994 to 1999) was consistent with estimates of N _E reported for 1992–2002. These results, coupled with in-depth census and exploitation data, show that the genetic characteristics of Escanaba Lake S. vitreus have changed substantially and that management activities, such as supplemental stocking and harvest practices, have profoundly influenced the genetic dynamics of S. vitreus in this lake.