Genetic diversity,admixture, and hatchery influence in Brook Trout (Salvelinus fontinalis) throughout western New York State

Although Brook Trout are distributed across most of eastern North America, population numbers have declined in many regions due to habitat loss, climate change, and competition with non‐native species. In New York State, Brook Trout habitat has been substantially reduced, with many areas showing complete extirpation of Brook Trout populations, predominantly in the western portion of the state. Small, fragmented populations are at risk of genetic diversity loss, inbreeding depression, and reduced fitness, leading to a greater potential for local extirpation. Genetic monitoring is a practical tool that can facilitate further conservation‐decision making regarding small populations. In this study, we used 12 microsatellite loci to examine 3,436 sampled Brook Trout, representing 75 sites from the Allegheny, Erie/Niagara, Genesee, Oswego, Lake Ontario, and Susquehanna drainage basins throughout western New York State. Three Brook Trout hatchery strains were also genetically characterized to evaluate the degree of hatchery introgression between wild populations and hatchery strains stocked in the region. Overall, estimates of genetic diversity varied widely: Allelic richness ranged from 2.23 to 7.485, and expected heterozygosity ranged from 0.402 to 0.766. As observed for Brook Trout in other regions, we found a high degree of genetic differentiation among populations, with all comparisons except one showing significant F_ST values. Hatchery introgression was found to be minimal, with estimates ranging from 1.96% to 3.10% of wild individuals exhibiting membership proportions to a hatchery strain cluster exceeding 10% (q ≥ 0.10). Results from this investigation can be used to prioritize management efforts for Brook Trout in western New York State and act as a baseline to monitor future population trends.     

Concomitant Antibiotic and Mercury Resistance Among Gastrointestinal Microflora of Feral Brook Trout, Salvelinus fontinalis

Twenty-nine bacterial isolates representing eight genera from the gastrointestinal tracts of feral brook trout Salvelinus fontinalis (Mitchell) demonstrated multiple maximal antibiotic resistances and concomitant broad-spectrum mercury (Hg) resistance. Equivalent viable plate counts on tryptic soy agar supplemented with either 0 or 25?μM HgCl₂ verified the ubiquity of mercury resistance in this microbial environment. Mercury levels in lake water samples measured 1.5?ng?L^?1; mercury concentrations in fish filets ranged from 81.8 to 1,080?ng?g^?1 and correlated with fish length. The presence of similar antibiotic and Hg resistance patterns in multiple genera of gastrointestinal microflora supports a growing body of research that multiple selective genes can be transferred horizontally in the presence of an unrelated individual selective pressure. We present data that bioaccumulation of non-point source Hg pollution could be a selective pressure to accumulate both antibiotic and Hg resistant bacteria.     

硬头鳟与溪红点鲑杂交三倍体育种技术的初步研究

为了获得同时具有杂交及三倍体优势的鲑鳟鱼苗种,开展了利用6-二甲基氨基嘌呤(6-DMAP)诱导硬头鳟(Oncorhynchus mykiss)、溪红点鲑(Salvelinus fontinalis)正反杂交受精卵的实验。杂交结果,溪红点鲑(♀)×硬头鳟(♂)实验组卵子在受精10 min后全部死亡,而硬头鳟(♀)×溪红点鲑(♂)组的受精卵正常,可以进行6-DMAP三倍体诱导实验。6-DMAP诱导受精卵结果,起始诱导时间在12~15 min,受精卵的发眼率最高,为75.87%~76.64%,在5个起始诱导时间梯度内,受精卵的孵化率在86.44%~90.31%之间,苗种三倍体率在92.45%~95.55%之间,差异不显著(P0.05)。诱导持续时间为10~15 min时,受精卵发眼率达到最高,为74.28%~76.81%,在5个诱导持续时间梯度内,受精卵孵化率在87.28%~90.24%之间,苗种三倍体率在93.67%~96.25%之间,变化不显著(P0.05)。药物诱导浓度为120~150 mg/L时,受精卵的发眼率达到最高,为73.57%~76.27%,在5个不同的药物浓度梯度内,受精卵孵化率在88.57%~90.03%之间,苗种三倍体率在92.56%~96.38%之间,变化不显著(P0.05)。结果表明,利用6-DMAP诱导受精卵制备杂交三倍体苗种的方法是可行的,实验最佳方法为硬头鳟(♀)×溪红点鲑(♂)卵子受精后12~15 min内,利用浓度为120~150 mg/L的6-DMAP溶液诱导,持续时间为10~15 min,然后放入孵化桶内正常孵化,获得苗种的三倍体率可达92.56%~96.38%,可满足正常生产的需要。     

Limestone Treatment of Whetstone Brook, Massachusetts. II. Changes in the Brown Trout (Salmo trutta)and Brook Trout (Salvelinus fontinalis)Fishery

Density, age structure, and growth rates of wild brook trout (Salvelinus fontinalis)and brown trout (Salmo trutta)in Whetstone Brook in northcentral Massachusetts were monitored for 4 years before and 3 years during limestone treatment to mitigate acidic conditions. The population density of brook trout increased significantly during treatment. Liming did not have any significant effects on the growth rates of brook trout or brown trout. Actual survival rates of brook trout and brown trout were not calculated due to the low density of both species, but more older individuals of both species were captured during the treatment period. Fulton condition factors (an index of fish condition) increased significantly for both brook trout and brown trout during treatment. Seven-day in situ bioassays of brown trout and rainbow trout demonstrated that liming improved the chemical environment for fish in Whetstone Brook. During a pretreatment bioassay in 1987, 100% rainbow trout mortality was observed at both the control and treatment stations in Whetstone Brook. Brown trout mortality was 67% in the control station and 70% in the treatment station. The pH during the 1987 bioassay averaged 4.90 in the control station and 4.99 in the treated station. During a bioassay conducted in 1990 after treatment began, rainbow trout mortality was 100% in the control station and 0% in the treatment station. Brown trout mortality was 17% in the control station and 0% in the treatment station. The pH during the 1990 bioassay averaged 5.23 in the control station and 6.60 in the treatment station. Analysis of total aluminum in the gills of fish from the 1990 bioassay revealed higher levels in fish from the control station than in those from the treatment station.     

Occurrence of Salmincola sp. on brook charr Salvelinus fontinalis in Lake Superior

Hydrobiologia - Salmincola sp. infect fishes of the family Salmonidae and can negatively affect host health. The parasite–host relationship was examined between Salmincola sp. and a remnant...     

Distribution of Telomeric DNA Sequences on the X-Radiation-Induced Chromosome Fragments Observed in the Genome of Androgenetic Brook Trout ( Salvelinus fontinalis , Mitchill 1814)

Cytogenetic screening of the androgenetic brook trout (Salvelinus fontinalis, Mitchill 1814) offspring hatched from eggs exposed to 420 Gy of X-radiation before insemination exhibited residues of the irradiated maternal nuclear genome in the form of small chromosome fragments. Remnants of the irradiated chromosomes had different sizes, and their number varied intraindividually from 1 to 15. To efficiently pass through the series of the cell divisions, such chromosome fragments must have had functional kinetochores. Distribution patterns of the telomeric hybridization signals on the chromosome fragments enabled us to distinguish their 3 groups: (i) telomere-less ring chromosomes with fused broken chromosome arms, (ii) rings formed in the course of fusion of the radiation-broken chromosome arm with the opposite telomeric region and exhibiting interstitial telomeric signals at the fusion point, and (iii) chromosome fragments with fused unprotected sister chromatids of 1 broken arm and intact telomeres from the other arm. Disturbances during segregation of such fragments, mainly breakages during anaphase, may partially explain intraindividual variation in the number and size of the chromosome fragments observed in the androgenetic brook trout.     

引进美洲红点鲑群体遗传多样性微卫星的分析

为了解引进种美洲红点鲑种群遗传结构和种质资源现状,本研究利用15个微卫星标记对其养殖群体遗传多样性进行了分析。结果表明:在30个个体中,15对微卫星引物除1对扩增产物为单态外,其余14对在美洲红点鲑群体内扩增均出现了多态,14个多态性位点等位基因数目为3～7不等,共检测到等位基因数为69个,平均有效等位基因数为3.03;期望杂合度在0.540～0.809之间,平均期望杂合度为0.664;多态信息含量在0.360～0.719之间,平均多态信息含量为0.578,表明引进的美洲红点鲑遗传多样性水平较高,具有良好的选育潜力,可以作为良好的育种材料。     

Behaviour-Genetics of Lake Charr (Salvelinus namaycush) and Brook Charr (S. fontinalis): Observation of Backcross and F2 Generations

Brook charr (Salvelinus fontinalis) defend territories and show high levels of agonistic behaviour. In contrast, lake charr (S. namaycush) are non-territorial and rarely show any agonistic behaviour. The genetic determinance of behavioural differences between these species was confirmed by the behavioural similarity of brook charr backcross hybrids and brook charr and a significant maternal effect on hybrid behavioural phenotypes. Backcross and F₂ generations showed either one of two distinct behavioural strategies, one aggressive and territorial and the other non-aggressive and non-territorial. It seems most likely that these strategies are conditional on individual phenotypes, such as size of nearby conspecifics. However, precise measurements of costs and benefits of each strategy are required to distinguish between these alternate hypotheses for either species. Each action pattern was an independent pattern of variation and a distinct behavioural unit. However, patterns were coordinated with all other patterns at a higher hierarchical level (corresponding to the particular behavioural strategy). It seems most likely that these strategies would be controlled by a polygenic system, even though the nature of our data does not allow us to make firm conclusions in this regard.     

Divergence in physiological factors affecting swimming performance between anadromous and resident populations of brook charr Salvelinus fontinalis

In this study, an anadromous strain (L) and a freshwater‐resident (R) strain of brook charr Salvelinus fontinalis as well as their reciprocal hybrids, were reared in a common environment and submitted to swimming tests combined with salinity challenges. The critical swimming speeds (U_crit) of the different crosses were measured in both fresh (FW) and salt water (SW) and the variations in several physiological traits (osmotic, energetic and metabolic capacities) that are predicted to influence swimming performance were documented. Anadromous and resident fish reached the same U_crit in both FW and SW, with U_crit being 14% lower in SW compared with FW. The strains, however, seemed to use different underlying strategies: the anadromous strain relied on its streamlined body shape and higher osmoregulatory capacity, while the resident strain had greater citrate synthase (FW) and lactate dehydrogenase (FW, SW) capacity and either greater initial stores or more efficient use of liver (FW, SW) and muscle (FW) glycogen during exercise. Compared with R_♀L_♂ hybrids, L_♀R_♂ hybrids had a 20% lower swimming speed, which was associated with a 24% smaller cardio‐somatic index and higher physiological costs. Thus swimming performance depends on cross direction (i.e. which parental line was used as dam or sire). The study thus suggests that divergent physiological factors between anadromous and resident S. fontinalis may result in similar swimming capacities that are adapted to their respective lifestyles.     

Genetic signatures of historical bottlenecks in sympatric lake trout (Salvelinus namaycush) morphotypes in Lake Superior

Humans have played a significant role in reducing levels of genetic diversity and differentiation of many teleost fishes, leading to homogenization across biological entities. We compare patterns of historical and contemporary genetic structure for three sympatric Great Lake??s lake trout (Salvelinus namaycush) morphs (lean, siscowet, and humper) that differ in patterns of habitat occupancy, susceptibility to overfishing and predation by invasive sea lamprey (Petromyzon marinus). Differential susceptibilities to overfishing and predation were expected to result in different impacts to levels of genetic diversity loss for each morphotype. Genetic data was collected for samples at three points in time: 1948 (pre-collapse), 1959 (collapse) and 1990s (current), corresponding to periods of intensive fishing, mortality due to lamprey and recovery, respectively. The lean morph preferentially targeted by the fishery and recognized as highly preyed upon by sea lamprey was more highly impacted genetically than other morphs, as evidenced by greater loss of genetic diversity first during the period of overfishing, then during the period of high sea lamprey abundance once the fishery collapsed. The siscowet morph also experienced genetic bottlenecks during the period of overfishing (pre-collapse period). Results indicate significant levels of genetic differentiation among morphs historically prior to declines in abundance and also among contemporary populations, suggesting that periods of population decline and resurgence in abundance and distribution did not result in loss of genetic distinctiveness among morphs.     

Adaptive and maladaptive genetic diversity in small populations: Insights from the Brook Charr (Salvelinus fontinalis) case study

Investigating the relative importance of neutral versus selective processes governing the accumulation of genetic variants is a key goal in both evolutionary and conservation biology. This is particularly true in the context of small populations, where genetic drift can counteract the effect of selection. Using Brook Charr (Salvelinus fontinalis) from Québec, Canada, as a case study, we investigated the importance of demographic versus selective processes governing the accumulation of both adaptive and maladaptive mutations in closed versus open and connected populations to assess gene flow effect. This was achieved by using 14,779 high‐quality filtered SNPs genotyped among 1,416 fish representing 50 populations from three life history types: lacustrine (closed populations), riverine and anadromous (connected populations). Using the PROVEAN algorithm, we observed a considerable accumulation of putative deleterious mutations across populations. The absence of correlation between the occurrence of putatively beneficial or deleterious mutations and local recombination rate supports the hypothesis that genetic drift might be the main driver of the accumulation of such variants. However, despite a lower genetic diversity observed in lacustrine than in riverine or anadromous populations, lacustrine populations do not exhibit more deleterious mutations than the two other history types, suggesting that the negative effect of genetic drift in lacustrine populations may be mitigated by that of relaxed purifying selection. Moreover, we also identified genomic regions associated with anadromy, as well as an overrepresentation of transposable elements associated with variation in environmental variables, thus supporting the importance of transposable elements in adaptation.     

Long-term suppression of the Lake Trout (Salvelinus namaycush) population in Lake Pend Oreille,Idaho

Hydrobiologia - A simulation model of lake trout Salvelinus namaycush (Walbaum 1792) population dynamics in Lake Pend Oreille, Idaho, was used to estimate (1) the optimal allocation of effort among...     

Genetic Divergence in Mandible Form in Relation to Molecular Divergence in Inbred Mouse Strains

Genetic divergence in the form of the mandible is examined in ten inbred strains of mice. Several univariate and multivariate genetic distance estimates are given for the morphological data and these estimates are compared to measures of genealogical and molecular divergence. Highly significant divergence occurs among the ten strains in all 11 mandible traits considered individually and simultaneously. Genealogical relationship among strains is highly correlated with genetic divergence in single locus molecular traits. However, the concordance between genealogical relationship and multivariate genetic divergence in morphology is much more complex. Whether there is a significant correlation between morphological divergence and genealogy depends upon the method of analysis and the particular genetic distance statistic being employed.     

Evolution and origin of sympatric shallow-water morphotypes of Lake Trout,Salvelinus namaycush,in Canada's Great Bear Lake

Range expansion in north-temperate fishes subsequent to the retreat of the Wisconsinan glaciers has resulted in the rapid colonization of previously unexploited, heterogeneous habitats and, in many situations, secondary contact among conspecific lineages that were once previously isolated. Such ecological opportunity coupled with reduced competition likely promoted morphological and genetic differentiation within and among post-glacial fish populations. Discrete morphological forms existing in sympatry, for example, have now been described in many species, yet few studies have directly assessed the association between morphological and genetic variation. Morphotypes of Lake Trout, Salvelinus namaycush, are found in several large-lake systems including Great Bear Lake (GBL), Northwest Territories, Canada, where several shallow-water forms are known. Here, we assess microsatellite and mitochondrial DNA variation among four morphotypes of Lake Trout from the five distinct arms of GBL, and also from locations outside of this system to evaluate several hypotheses concerning the evolution of morphological variation in this species. Our data indicate that morphotypes of Lake Trout from GBL are genetically differentiated from one another, yet the morphotypes are still genetically more similar to one another compared with populations from outside of this system. Furthermore, our data suggest that Lake Trout colonized GBL following dispersal from a single glacial refugium (the Mississippian) and support an intra-lake model of divergence. Overall, our study provides insights into the origins of morphological and genetic variation in post-glacial populations of fishes and provides benchmarks important for monitoring Lake Trout biodiversity in a region thought to be disproportionately susceptible to impacts from climate change.     

Tc1-Like Transposable Elements in the Genome of Lake Trout (Salvelinus namaycush)

This study reports on the DNA sequence of a Tc1-like transposable element Tsn1 from lake trout (Salvelinus namaycush). Tc1-like elements were amplified by PCR using an oligonucleotide primer based on the Tdr1 element of zebrafish. One full-length and two partial-length copies of the transposon were sequenced. In addition, partial Tsn1 elements were recovered from PCR reactions run with primers specific to the 3′ terminus of the 28S rDNA. However, sequence analysis of cloned fragments found that these sequences were not associated with the rDNA cistron. Sequence comparisons indicate that Tsn1 is a type A element common to both salmonid and cyprinid fishes. The consensus sequence of the full-length element (Tsn1) was 1643 nucleotides with long terminal repeats (LTRs) of 225 nucleotides. Tsn1 contains a transposase coding region corresponding to 340 amino acids that includes all of the functional elements of Tc1-like transposons. Southern analysis found a high proportion of the Tsn1 transposons in the lake trout genome to be full-length copies. Received March 7, 1998; accepted July 20, 1998