Disentangling stocking introgression and natural migration in brown trout: survival success and recruitment failure in populations with semi‐supportive breeding

1. Introgression into natural salmonid populations from stocked conspecifics has been widely studied. Outcomes vary from no effect even after decades of stocking, to population replacement after only a couple of generations. Potential introgression caused by semi‐supportive breeding (i.e. using a mixture of local strains as brood stock) is, however, less well studied. 2. We investigated population structure of brown trout (Salmo trutta) in a regulated alpine lake with three natural, environmentally contrasting tributaries used as spawning and rearing habitat. Massive semi‐supportive breeding of admixed local strains has been implemented for decades. Stocked trout represented c. 17% of the total lake population, and a substantial post‐release survival reflects a considerable potential for introgression. However, the mark‐recapture studies indicate no spawning runs of stocked fish. 3. Using 13 polymorphic microsatellite loci, we found natural straying and non‐native reproduction, especially among wild populations inhabiting environmentally unstable habitat. Retained genetic structure across tributaries indicated low reproductive success of wild‐born non‐natives. Moreover, the genetic structure among tributaries has probably not been influenced by semi‐supportive breeding, because of recruitment failure of stocked trout.     

Dynamic micro-geographic and temporal genetic diversity in vertebrates: the case of lake-spawning populations of brown trout (Salmo trutta)

Conservation of species should be based on knowledge of effective population sizes and understanding of how breeding tactics and selection of recruitment habitats lead to genetic structuring. In the stream‐spawning and genetically diverse brown trout, spawning and rearing areas may be restricted source habitats. Spatio–temporal genetic variability patterns were studied in brown trout occupying three lakes characterized by restricted stream habitat but high recruitment levels. This suggested non‐typical lake‐spawning, potentially representing additional spatio–temporal genetic variation in continuous habitats. Three years of sampling documented presence of young‐of‐the‐year cohorts in littoral lake areas with groundwater inflow, confirming lake‐spawning trout in all three lakes. Nine microsatellite markers assayed across 901 young‐of‐the‐year individuals indicated overall substantial genetic differentiation in space and time. Nested gene diversity analyses revealed highly significant (≤P = 0.002) differentiation on all hierarchical levels, represented by regional lakes (F_LT = 0.281), stream vs. lake habitat within regional lakes (F_HL = 0.045), sample site within habitats (F_SH = 0.010), and cohorts within sample sites (F_CS = 0.016). Genetic structuring was, however, different among lakes. It was more pronounced in a natural lake, which exhibited temporally stable structuring both between two lake‐spawning populations and between lake‐ and stream spawners. Hence, it is demonstrated that lake‐spawning brown trout form genetically distinct populations and may significantly contribute to genetic diversity. In another lake, differentiation was substantial between stream‐ and lake‐spawning populations but not within habitat. In the third lake, there was less apparent spatial or temporal genetic structuring. Calculation of effective population sizes suggested small spawning populations in general, both within streams and lakes, and indicates that the presence of lake‐spawning populations tended to reduce genetic drift in the total (meta‐) population of the lake.     

Identifying footprints of selection in stocked brown trout populations: a spatio‐temporal approach

Studies of interactions between farmed and wild salmonid fishes have suggested reduced fitness of farmed strains in the wild, but evidence for selection at the genic level is lacking. We studied three brown trout populations in Denmark which have been significantly admixed with stocked hatchery trout (19–64%), along with two hatchery strains used for stocking. The wild populations were represented by contemporary samples (2000–2006) and two of them by historical samples (1943–1956). We analysed 61 microsatellite loci, nine of which showed putative functional relationships [expressed sequence tag (EST)‐linked or quantitative trait loci]. F_ST‐based outlier tests provided support for diversifying selection at chromosome regions marked by three loci, two anonymous and one EST‐linked. Patterns of differentiation suggested that the loci were candidates for being under diversifying hitch‐hiking selection in hatchery vs. wild environments. Analysis of hatchery strain admixture proportions showed that in one wild population, two of the loci showed significantly lower admixture proportions than the putatively neutral loci, implying contemporary selection against alleles introduced by hatchery strain trout. In the most strongly admixed population, however, there was no evidence for selection, possibly because of immigration by stocked trout overcoming selection against hatchery‐derived alleles or supportive breeding practices allowing hatchery strain trout to escape natural selection. To our knowledge, this is the first study demonstrating footprints of selection in wild salmonid populations subject to spawning intrusion by farmed fish.     

High level of population genetic structuring in lake-run brown trout, Salmo trutta, of the Inari Basin, northern Finland

Rivers draining into (Lake) Inarijärvi, northern Finland, sustain a number of lake‐run brown trout, Salmo trutta, populations but, as with most lake‐run S. trutta systems, the level of population genetic structuring among populations is unknown. To address this and to assist fish stock management in the region, the population genetic structure of S. trutta collected from 28 sampling sites in rivers flowing into Inarijärvi was studied using 13 microsatellite loci. Populations were clustered into three separate groups, largely corresponding to geographic regions, with between‐region F_ST values ranging from 0·11 to 0·16. The significant differentiation observed between most populations within each region also implies that individual populations should be recognized as separate management units and actions to improve, and subsequently maintain, conditions for natural spawning should be prioritized. The results of this study further indicate that the trout from each of these regions may have different biological characteristics, such as local‐lake feeding behaviour among the western populations and strong isolation among the northern stocks. As a consequence, further research is warranted to better understand the level of ecological uniqueness of lake‐run S. trutta populations.     

Contrasting genetic metrics and patterns among naturalized rainbow trout (Oncorhynchus mykiss) in two Patagonian lakes differentially impacted by trout aquaculture

Different pathways of propagation and dispersal of non‐native species into new environments may have contrasting demographic and genetic impacts on established populations. Repeated introductions of rainbow trout (Oncorhynchus mykiss) to Chile in South America, initially through stocking and later through aquaculture escapes, provide a unique setting to contrast these two pathways. Using a panel of single nucleotide polymorphisms, we found contrasting genetic metrics and patterns among naturalized trout in Lake Llanquihue, Chile's largest producer of salmonid smolts for nearly 50 years, and Lake Todos Los Santos (TLS), a reference lake where aquaculture has been prohibited by law. Trout from Lake Llanquihue showed higher genetic diversity, weaker genetic structure, and larger estimates for the effective number of breeders (N_b) than trout from Lake TLS. Trout from Lake TLS were divergent from Lake Llanquihue and showed marked genetic structure and a significant isolation‐by‐distance pattern consistent with secondary contact between documented and undocumented stocking events in opposite shores of the lake. Multiple factors, including differences in propagule pressure, origin of donor populations, lake geomorphology, habitat quality or quantity, and life history, may help explain contrasting genetic metrics and patterns for trout between lakes. We contend that high propagule pressure from aquaculture may not only increase genetic diversity and N_b via demographic effects and admixture, but also may impact the evolution of genetic structure and increase gene flow, consistent with findings from artificially propagated salmonid populations in their native and naturalized ranges.     

A reintroduced lake sturgeon population comes of age: A genetic evaluation of stocking success in the St. Louis River

Lake sturgeon (Acipenser fulvescens) have experienced significant declines throughout the Great Lakes, leading to stocking efforts at some locations to reestablish extirpated populations. Given the late sexual maturity of the species, assessment of stocking program success is often delayed. Lake sturgeon were extirpated from the St. Louis River in western Lake Superior. Stocking began in 1983 and continued until 1994, using the Wolf River (Lake Winnebago) in the Lake Michigan basin as the source. Stocking resumed from 1998 to 2000, using the Sturgeon River in Lake Superior as the source. Our objectives were to (a) determine the movement patterns of stocked Wolf River sturgeon, (b) determine whether stocked individuals are migrating into natural spawning populations during the spawning season, (c) identify the origins of individuals captured in the St. Louis River, and (d) assess the genetic diversity of the reintroduced St. Louis River population. All collected samples were analyzed using 12 microsatellite loci, followed by genetic assignment testing to achieve the first three objectives. Genetic diversity was compared to natural spawning populations in Lake Superior. The highest proportion of stocked Wolf River lake sturgeon was detected in western Lake Superior, close to the stocking site. However, individuals were detected throughout Lake Superior. Wolf River individuals were detected in most of the spawning populations in Lake Superior, with the greatest number in the Sturgeon River and the Goulais River. The majority of individuals captured in the St. Louis River were of stocked origin (88.1%), with 73.5% from the Wolf River and 14.6% from the Sturgeon River. These observed proportions differed from the expected proportions based on the number of sturgeon released from each source (χ² = 55.37, p < 0.00001), with a higher representation of Sturgeon River individuals. Evidence of natural recolonization in the St. Louis River was detected from Lake Huron and Goulais River individuals. Genetic diversity of the St. Louis River population was comparable to levels observed in the remnant natural populations in Lake Superior. However, the effective population size of the St. Louis River was small (N_e = 38.1) and average relatedness among individuals was relatively high (r = 0.151). Monitoring of movement of stocked Wolf River sturgeon throughout Lake Superior should continue, with careful attention to the potential for outbreeding depression in remnant populations. Genetic diversity of the St. Louis River population should also continue to be monitored to see if it improves with increased natural reproduction.     

Effects of sea trout stocking on the population genetics of landlocked brown trout, Salmo trutta L., in the Conwy River system, North Wales, U.K.

The effect of the introduction of fry of anadromous sea trout, Salmo trutta L., on the genetic integrity of landlocked brown trout populations was evaluated. Samples were taken from six brown trout populations from streams above impassable waterfalls in the Conwy river system (North Wales, U.K.) in 1989 and 1990. Three of these streams had no known stocking history and three had been stocked with sea trout fry from the lower Conwy system over the last few years. Representatives of these sea trout were collected from two streams in the lower Conwy system and from a hatchery. Allele frequencies at 13 loci, six of which were polymorphic, were determined by starch gel electrophoresis.
The stocked populations were intermediate in their allele frequencies between unstocked brown trout and sea trout samples. A principal component analysis suggested significant numbers of hybrids in all of the stocked streams. This shows that some of the introduced sea trout did not migrate down the falls to the sea, but stayed in fresh water and hybridized with the local population. The significance of this finding for the conservation of the genetic resource of brown trout stocks is discussed.     

Microsatellite and mtDNA analysis of lake trout,Salvelinus namaycush,from Great Bear Lake,Northwest Territories: impacts of historical and contemporary evolutionary forces on Arctic ecosystems

Resolving the genetic population structure of species inhabiting pristine, high latitude ecosystems can provide novel insights into the post‐glacial, evolutionary processes shaping the distribution of contemporary genetic variation. In this study, we assayed genetic variation in lake trout (Salvelinus namaycush) from Great Bear Lake (GBL), NT and one population outside of this lake (Sandy Lake, NT) at 11 microsatellite loci and the mtDNA control region (d‐loop). Overall, population subdivision was low, but significant (global F_ST θ = 0.025), and pairwise comparisons indicated that significance was heavily influenced by comparisons between GBL localities and Sandy Lake. Our data indicate that there is no obvious genetic structure among the various basins within GBL (global F_ST = 0.002) despite the large geographic distances between sampling areas. We found evidence of low levels of contemporary gene flow among arms within GBL, but not between Sandy Lake and GBL. Coalescent analyses suggested that some historical gene flow occurred among arms within GBL and between GBL and Sandy Lake. It appears, therefore, that contemporary (ongoing dispersal and gene flow) and historical (historical gene flow and large founding and present‐day effective population sizes) factors contribute to the lack of neutral genetic structure in GBL. Overall, our results illustrate the importance of history (e.g., post‐glacial colonization) and contemporary dispersal ecology in shaping genetic population structure of Arctic faunas and provide a better understanding of the evolutionary ecology of long‐lived salmonids in pristine, interconnected habitats.     

Evidence for selective angling of introduced trout and their hybrids in a stocked brown trout population

Comparisons of the genetic composition of brown trout Salmo trutta captured by anglers and by electrofishing based on three diagnostic microsatellite loci provided strong evidence that angling is selective in a stocked brown trout population. At two sites, anglers caught significantly younger trout and proportionally more introduced hatchery trout and hybrids than were observed in electrofishing surveys. Selective angling, in combination with a small legal catch size, may have considerably eliminated introduced trout and hybrids before spawning at the study sites, and thus may have reduced the introgression of alien genes into the local gene pool. Angling can be an important factor influencing the genetic structure of fish populations and should be taken into account in studies of introgressive hybridization in stocked fish populations and their management. In this study, demographic consequences of stocking were not assessed. Thus, even though the genetic consequences of stocking may be minimal or largely reversible through angling, resource competition between native and introduced trout, until they reach legal catch size, is expected to have a negative effect on the productivity of the indigenous trout population.     

Impacts of acidification on brown trout Salmo trutta populations and the contribution of stocking to population recovery and genetic diversity

Anthropogenic acidification in SW-Scotland, from the early 19th Century onwards, led to the extinction of several loch (lake) brown trout (Salmo trutta) populations and substantial reductions in numbers in many others. Higher altitude populations with no stocking influence, which are isolated above natural and artificial barriers and subjected to the greatest effect of acidification, exhibited the least intrapopulation genetic diversity (34% of the allelic richness of the populations accessible to anadromous S. trutta). These, however, were characterised by the greatest interpopulation divergence (highest pairwise D_EST 0.61 and F_ST 0.53 in contemporary samples) based on 16 microsatellite loci and are among the most differentiated S. trutta populations in NW-Europe. Five lochs above impassable waterfalls, where S. trutta were thought to be extinct, are documented as having been stocked in the late 1980s or 1990s. All five lochs now support self-sustaining S. trutta populations; three as a direct result of restoration stocking and two adjoining lochs largely arising from a small remnant wild population in one, but with some stocking input. The genetically unique Loch Grannoch S. trutta, which has been shown to have a heritable increased tolerance to acid conditions, was successfully used as a donor stock to restore populations in two acidic lochs. Loch Fleet S. trutta, which were re-established from four separate donor sources in the late 1980s, showed differential contribution from these ancestors and a higher genetic diversity than all 17 natural loch populations examined in the area. Genetically distinct inlet and outlet spawning S. trutta populations were found in this loch. Three genetically distinct sympatric populations of S. trutta were identified in Loch Grannoch, most likely representing recruitment from the three main spawning rivers. A distinct genetic signature of Loch Leven S. trutta, the progenitor of many Scottish farm strains, facilitated detection of stocking with these strains. One artificially created loch was shown to have a population genetically very similar to Loch Leven S. trutta. In spite of recorded historical supplemental stocking with Loch Leven derived farm strains, much of the indigenous S. trutta genetic diversity in the area remains intact, aside from the effects of acidification induced bottlenecks. Overall genetic diversity and extant populations have been increased by allochthonous stocking.     

Life history and ecological characteristics of humper and lean ecotypes of lake trout stocked in Lake Erie

Through combined effects of over-exploitation and predation by invasive non-native sea lamprey Petromyzon marinus (Linneaus 1958), the lake trout Salvelinus namaycush (Walbaum 1972) population in Lake Erie collapsed and was considered extirpated by 1950; annual stocking occurred in 1969 to bolster and maintain this population as natural recruitment ceased. While various hatchery strains of lean ecotype lake trout remain the focus of Lake Erie’s stocking, between 2004 and 2011 a humper-like ecotype was stocked to aid re-establishment efforts. We assessed ecotype performance via adult fish collected during the summer-stratified period (2004–2017) and evaluated if life history and ecological characteristics varied between stocked ecotypes. Ecotype-specific differences in survival, length-at-age, accumulation of weight with length, and diet were observed. Lean lake trout grew faster (length-at-age) and matured at larger sizes than the humper ecotype. Humper lake trout exhibited higher sea lamprey wounding and lower survival rates than lean lake trout. Humpers also consumed more benthic prey fish than lean lake trout, suggesting this ecotype may exhibit a more benthic orientation than leans. Our study represents the first evaluation of how a non-lean ecotype lake trout performs outside their native ecosystem and provides fishery managers with valuable information relevant to re-establishing lake trout populations in the Great Lakes.

     

Investigating the extent of parallelism in morphological and genomic divergence among lake trout ecotypes in Lake Superior

Understanding the emergence of species through the process of ecological speciation is a central question in evolutionary biology which also has implications for conservation and management. Lake trout (Salvelinus namaycush) is renowned for the occurrence of different ecotypes linked to resource and habitat use throughout North America. We aimed to unravel the fine genetic structure of the four lake trout ecotypes in Lake Superior. A total of 486 individuals from four sites were genotyped at 6822 filtered SNPs using RADseq technology. Our results revealed different extent of morphological and genetic differentiation within the different sites. Overall, genetic differentiation was weak but significant and was on average three times higher between sites (mean F_ST = 0.016) than between ecotypes within sites (mean F_ST = 0.005) indicating higher level of gene flow or a more recent shared ancestor between ecotypes within each site than between populations of the same ecotype. Evidence of divergent selection was also found between ecotypes and/or in association with morphological variation. Outlier loci found in genes related to lipid metabolism and visual acuity were of particular interest in this context of ecotypic divergence. However, we did not find clear indication of parallelism at the genomic level, despite the presence of phenotypic parallelism among some ecotypes from different sampling sites. Overall, the occurrence of different levels of both genomic and phenotypic differentiation between ecotypes within each site with several differentiated loci linked to relevant biological functions supports the presence of a continuum of divergence in lake trout.     

Admixture analysis of stocked brown trout populations using mapped microsatellite DNA markers: indigenous trout persist in introgressed populations

Admixture between wild and captive populations is an increasing concern in conservation biology. Understanding the extent of admixture and the processes involved requires identification of admixed and non-admixed individuals. This can be achieved by statistical methods employing Bayesian clustering, but resolution is low if genetic differentiation is weak. Here, we analyse stocked brown trout populations represented by historical (1943–1956) and contemporary (2000s) samples, where genetic differentiation between wild populations and stocked trout is weak (pairwise F_ST of 0.047 and 0.053). By analysing a high number of microsatellite DNA markers (50) and making use of linkage map information, we achieve clear identification of admixed and non-admixed trout. Moreover, despite strong population-level admixture by hatchery strain trout in one of the populations (70.8%), non-admixed individuals nevertheless persist (7 out of 53 individuals). These remnants of the indigenous population are characterized by later spawning time than the majority of the admixed individuals. We hypothesize that isolation by time mediated by spawning time differences between wild and hatchery strain trout is a major factor rescuing a part of the indigenous population from introgression.     

Hierarchical population structure and genetic diversity of lake trout (Salvelinus namaycush) in a dendritic system in Northern Labrador

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Estimating the long-term effects of stocking domesticated trout into wild brown trout (Salmo trutta) populations: an approach using microsatellite DNA analysis of historical and contemporary samples

Indigenous salmonid fish gene pools are affected by domesticated conspecifics, derived from aquaculture escapes and deliberate releases. Variability was examined at nine microsatellite loci in order to assess the long-term impact of stocking domesticated trout in two brown trout populations. The study was based on analysis of two historical samples (1945-56), represented by old scale collections, and seven contemporary samples (1986-2000). In one population historical and contemporary samples were remarkably genetically similar despite more than a decade of intense stocking. Estimation of admixture proportions showed a small genetic contribution from domesticated trout (approximately 6%), and individual admixture analysis demonstrated a majority of nonadmixed individuals. The expected genetic contribution by domesticated trout was 64%, assessed from the number of stocked trout and assuming equal survival and reproductive performance of wild and domesticated trout. This demonstrates poor performance and low fitness of domesticated trout in the wild. In another population there was a strong genetic contribution from domesticated trout (between 57% and 88% in different samples), both in samples from a broodstock thought to represent the indigenous population and in a sample of wild spawners. Survival of domesticated trout and admixture with indigenous fish in the broodstock and subsequent stocking into the river, combined with a low population size of native trout relative to the number of stocked trout, could explain the observed introgression. Few nonadmixed individuals remained in the introgressed population, and I discuss how individual admixture analysis can be used to identify and conserve nonintrogressed remains of the population.     

Effects of vitamin B1 (thiamine) deficiency in lake trout (Salvelinus namaycush) alevins at hatching stage

The objectives of this study were to examine the relationship between thiamine concentrations in unfertilized eggs and yolksac individuals of lake trout (Salvelinus namaycush), along with any associated histopathological changes in the tissues of alevins at the hatching stage. We address these questions in a lake trout population from different spawning grounds of Lake Michigan (North and South), known for compromised survival due to early mortality syndrome (EMS). However, a dichotomous forage base of lake trout spawning stocks, with a dietary thiaminase-rich alewife in the North, and dietary low-thiaminase round goby in the South, provides the basis for the assumption that different diets may lead to differences in severity of EMS between different stocks. Lake trout eggs of 18 females were collected and fertilized individually with the sperm of several males. The eggs, eyed embryos and newly-hatched alevins were sampled to examine thiamine utilization during embryogenesis. Progenies of females with low (< 0.73 nmol/g) and high (> 0.85 nmol/g) levels of thiamine were chosen for histological studies. The obtained results showed that total thiamine levels in the body and yolk of eyed embryos and alevins at hatching were influenced by thiamine levels of unfertilized eggs and it decreased during embryogenesis (to 51% in eyed embryos and 28% in newly-hatched alevins in comparison to unfertilized eggs). The survival of lake trout until hatching stage does not correlate with the thiamine level, however it was affected by collection site and was significantly higher in fish from the South site (Julian's Reef). At the hatching stage, no pathological changes were observed in the brain, olfactory lobe, retina or liver in embryos regardless of thiamine concentrations in unfertilized eggs. It has been concluded that an enhanced thiamine requirement for the fast muscle mass growth near the swim-up stage is responsible for overt and histopathological signs of EMS. Current study confirms earlier findings that lake trout suffering from EMS can be successfully treated by immersion in thiamine solution as late as at the swim-up stage.     

Comparison of brook trout reproductive success and recruitment in an acidic adirondack lake following whole lake liming and watershed liming

Limestone applications to the catchment of one tributary to Woods Lake were highly effective in reducing stream acidity and stabilizing seasonal fluctuations in pH. The resulting improvement in stream water quality also led to a dramatic shift in reproductive strategy of the Woods Lake brook trout population. Prior to catchment liming, brook trout in Woods Lake were restricted to spawning on poor quality near shore substrate with limited ground water seepage. Reproductive success was limited by high mortality of eggs and larvae and recruitment from in lake spawning was not successful. Spawning brook trout did not utilize the tributary for spawning prior to watershed liming. Mitigation of acidity in the tributary, by catchment liming, effectively extended the spawning habitat available to the Woods Lake brook trout population and one year following treatment brook trout spawned successfully in the tributary for the first time in 6 years of observation. Significant recruitment of young trout into the lake population occurred from 1991 through 1993, although the absolute number of fish captured was relatively small. In the fall of 1993, four year classes of naturally spawned brook trout were present in the lake. Although reproductive success was enhanced by improving tributary spawning habitat in the Woods Lake basin, self maintenance of the population may be limited by low recruitment rates of young trout, due to high levels of summer mortality resulting from predation. Mitigation of this constraint would require substantially higher levels of fry production than were observed in Woods Lake and/or enhanced refugia for young trout. The results of this experiment suggest that re-establishment of tributary spawning populations of brook trout may be possible, with future reductions in acidic deposition, in acidic Adirondack lakes with limited in-lake spawning habitat.     

Migration barriers protect indigenous brown trout (<Emphasis Type="Italic">Salmo trutta</Emphasis>) populations from introgression with stocked hatchery fish

Brown trout populations in the Belgian rivers Scheldt and Meuse have been intensively stocked in the past decades, often with material of uncertain origin. Moreover, the species habitat has become increasingly fragmented, preventing gene flow between neighboring populations. We assessed how this impacted genetic diversity and population structure by analyzing 12 wild populations (total n=309) and seven hatchery stocks (n=200) at the mitochondrial control region with SSCP and at 27 RAPD loci. Historical records indicate that brown trout from distant locations have been used to supplement hatchery stocks; nevertheless we detected non-Atlantic mitochondrial genomes in only one population of the Scheldt basin and in one hatchery. In general, the hatchery samples displayed a higher genetic diversity and differentiated less among each other (global F_ST(mtDNA)=0.311/F_ST(RAPD)=0.029) compared to the wild populations (global F_ST(mtDNA)=0.477/F_ST(RAPD)=0.204). This is due to frequent exchanges between hatcheries and regular supplementation from several indigenous populations. Gene pools present in most downstream sections from tributaries of the Meuse were similar to each other and to the hatchery samples, despite the presence of migration barriers. Assignment analyses indicated that the contribution of hatchery material to the upstream parts was limited or even completely absent in populations separated by a physical barrier. Intensive stocking and exchange between hatcheries has homogenized the downstream sections of the Meuse River, whereas the migration barriers preserved the indigenous upstream populations. As such, uncontrolled removal of barriers might result in an irreversible loss of the remnant indigenous gene pools.     

Genetic and morphoecological characteristics of peled <Emphasis Type="Italic">Coregonus peled</Emphasis> acclimatized in lakes of Tuva Republic

Morphoecological and genetic characters were studied of peled Coregonus peled naturalized in lakes of Tuva Republic. For comparison (as a donor), peled was considered from Leningrad oblast to originate from “wild” peled from Lake Endyr and dispersed widely into water bodies of the former Soviet Union. The results of analysis of variations in 18 polymorphic nuclear loci, coding the proteins (allozymes), and the part of mitochondrial (mt)DNA, coding the first subunit of NADH-dehydrogenase, attest genetic and morphoecological differentiation of populations formed in Tuva lakes. Significant differences were found between them in age composition, rate of growth, and external morphology. Statistically significant differences in allele frequencies of some loci were observed between the samples of acclimatized peled, though total level of genetic differentiation between the populations was not high (F _ST = 0.028). Estimates of gene diversity by allozyme loci were maximal in the population of alpine Lake Sut-Khol, but almost minimum diversity of mtDNA was observed in this population. It is obvious that “own” genetic appearance is formed in introduced fishes in every lake with peculiar diversity in the result of interaction between relatively homogeneous donor material and specific conditions of new environment, and this interaction is especially intense at the first stages of introduction.     

Genetic Integrity and Microgeographic Population Structure of Westslope Cutthroat Trout, Oncorhynchus clarki lewisi, in the Pend Oreille Basin in Washington

Five microsatellite DNA loci (Ots-101 ^*,Ots-107 ^*,Oki-10 ^*, Ogo-3 ^*, and FGT-3 ^*) were screened to evaluate the genetic characteristics and population structure for cutthroat trout from eight tributaries of the Pend Oreille River in northeastern Washington and to compare these collections with two hatchery stocks of westslope cutthroat trout, Oncorhynchus clarki lewisi, Yellowstone cutthroat trout, Oncorhynchus clarki bouvieri and a hatchery rainbow trout, Oncorhynchus mykiss, strain that have been stocked in northeastern Washington. Relatively high levels of variation (numbers of alleles and heterozygosity) were observed in all collections and allele frequencies were quite variable among collections. Evidence of limited introgression by rainbow and/or Yellowstone cutthroat was found at several locations. Both F_ST values and tests of genetic differentiation indicated the existence of numerous, reproductively isolated populations. The population in Slate Creek was very similar to the Kings Lake Hatchery strain, and we conclude that this similarity is the result of historical introductions of this hatchery strain into what was presumably a stream without a native cutthroat population. In one stream, differences in introgression and allele frequencies were found above and below a barrier falls. Because of the substantial level of population differentiation observed among the various collections, we recommend that management and conservation actions be focused at the level of individual streams in order to maintain the productivity and genetic character of the existing populations of cutthroat trout.