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1.
Shannon E. Pittman Timothy L. King Søren Faurby Michael E. Dorcas 《Conservation Genetics》2011,12(6):1589-1601
In this study, we sought to determine the population stability and genetic diversity of one isolated population of the federally-threatened
bog turtle (Glyptemys muhlenbergii) in North Carolina. Using capture–recapture data, we estimated adult survival and population growth rate from 1992 to 2007.
We found that the population decreased from an estimated 36 adult turtles in 1994 to approximately 11 adult turtles in 2007.
We found a constant adult survival of 0.893 (SE = 0.018, 95% confidence interval, 0.853–0.924) between 1992 and 2007. Using
18 microsatellite markers, we compared the genetic status of this population with five other bog turtle populations. The target
population displayed allelic richness (4.8 ± 0.5) and observed heterozygosity (0.619 ± 0.064) within the range of the other
bog turtle populations. Coalescent analysis of population growth rate, effective population size, and timing of population
structuring event also indicated the genetics of the target population were comparable to the other populations studied. Estimates
of effective population size were a proportion of the census size in all populations except the target population, in which
the effective population size was larger than the census size (30 turtles vs. 11 turtles). We attribute the high genetic diversity
in the target population to the presence of multiple generations of old turtles. This study illustrates that the demographic
status of populations of long-lived species may not be reflected genetically if a decline occurred recently. Consequently,
the genetic integrity of populations of long-lived animals experiencing rapid demographic bottlenecks may be preserved through
conservation efforts effective in addressing demographic problems. 相似文献
2.
Mary Brooke McEachern Dirk H. Van Vuren Chris H. Floyd Bernie May John M. Eadie 《Conservation Genetics》2011,12(1):285-296
Mammal species characterized by highly fluctuating populations often maintain genetic diversity in response to frequent demographic
bottlenecks, suggesting the ameliorating influence of life history and behavioral factors. Immigration in particular is expected
to promote genetic recovery and is hypothesized to be the most likely process maintaining genetic diversity in fluctuating
mammal populations. Most demographic bottlenecks have been inferred retrospectively, and direct analysis of a natural population
before, during, and after a bottleneck is rare. Using a continuous 10-year dataset detailing the complete demographic and
genetic history of a fluctuating population of golden-mantled ground squirrels (Spermophilus lateralis), we analyzed the genetic consequences of a 4-year demographic bottleneck that reduced the population to seven adult squirrels,
and we evaluated the potential “rescue effect” of immigration. Analysis of six microsatellite loci revealed that, while a
decline in allelic richness was observed during the bottleneck, there was no observed excess of heterozygosity, a characteristic
bottleneck signature, and no evidence for heterozygote deficiency during the recovery phase. In addition, we found no evidence
for inbreeding depression during or after the bottleneck. By identifying immigrants and analyzing their demographic and genetic
contributions, we found that immigration promoted demographic recovery and countered the genetic effects of the bottleneck,
especially the loss of allelic richness. Within 3 years both population size and genetic variation had recovered to pre-bottleneck
levels, supporting the role of immigration in maintaining genetic variation during bottleneck events in fluctuating populations.
Our analyses revealed considerable variation among analytical techniques in their ability to detect genetic bottlenecks, suggesting
that caution is warranted when evaluating bottleneck events based on one technique. 相似文献
3.
Genetic diversity is often considered important for species that inhabit highly disturbed environments to allow for adaptation.
Many variables affect levels of genetic variation; however, the two most influential variables are population size and type
of reproduction. When analyzed separately, both small population size and asexual reproduction can lead to reductions in genetic
variation, although the exact nature of which can be contrasting. Genetic variables such as allelic richness, heterozygosity,
inbreeding coefficient, and population differentiation have opposite predictions depending upon the trait (rarity or clonality)
examined. The goal of this study was to quantify genetic variation and population differentiation in a species that resides
in a highly stochastic environment and is both rare and highly clonal, Spiraea virginiana, and to determine if one trait is more influential genetically than the other. From populations sampled throughout the natural
range of S. virginiana, we used microsatellite loci to estimate overall genetic variation. We also calculated clonal structure within populations,
which included genotypic richness, evenness, and diversity. Gene flow was investigated by quantifying the relationship between
genetic and geographic distances, and population differentiation (θ) among populations. Observed heterozygosity, genotypic richness, and inbreeding coefficients were found to be representative
of high clonal reproduction (averaging 0.505, 0.1, and –0.356, respectively) and the number of alleles within populations
was low (range = 2.0–3.6), being more indicative of rarity. Population differentiation (θ) among populations was high (average = 0.302) and there was no relationship between genetic and geographic distances. By
examining a species that exhibits two traits that both can lead to reduced genetic variation, we may find an enhanced urgency
for conservation. Accurate demographic counts of clonal species are rarely, if ever, possible and genetic exploration for
every species is not feasible. Therefore, the conclusions in this study can be potentially extrapolated to other riparian,
clonal shrubs that share similar biology as S. virginiana. 相似文献
4.
Jonathan M. Conard Mark J. Statham Philip S. Gipson Samantha M. Wisely 《Restoration Ecology》2010,18(Z1):85-93
Reintroduction of terrestrial vertebrates with the goal of ecosystem restoration typically establishes small and isolated populations that may experience reduced genetic variability due to founder effects and genetic drift. Understanding the genetic structure of these populations and maintaining adequate genetic diversity is important for long‐term restoration success. We quantified genetic variability at six microsatellite loci for a reintroduced population of Cervus elaphus (elk) restored to the tallgrass prairie ecosystem of northeastern Kansas. Allelic richness, observed and expected heterozygosity were intermediate to levels reported in other North American elk populations. Current levels of genetic variability in restored North American elk populations were not well explained by founding population size, number of founding populations, or number of years since the last translocation. Simulation results suggest that the retention of genetic variability in isolated populations is strongly influenced by mating system while also being impacted by temporal variability in population size and population growth rate. Our results have implications for understanding how translocation strategies and post‐reintroduction management may influence genetic variability in restored populations. 相似文献
5.
Hallvard Haanes Knut H. Røed Silvia Perez-Espona Olav Rosef 《European Journal of Wildlife Research》2011,57(6):1137-1150
Loss of genetic variation from genetic drift during population bottlenecks has been shown for many species. Red deer (Cervus elaphus) may have been exposed to bottlenecks due to founder events during postglacial colonisation in the early Holocene and during
known population reductions in the eighteenth and nineteenth centuries. In this study, we assess loss of genetic variation
in Scandinavian red deer due to potential bottlenecks by comparing microsatellite (n = 14) and mitochondrial DNA variation in the Norwegian and Swedish populations with the Scottish, Lithuanian and Hungarian
populations. Bottlenecks are also assessed from the M ratio of populations, heterozygosity excess and from hierarchical Bayesian
analyses of their demographic history. Strong genetic drift and differentiation was identified in both Scandinavian populations.
Microsatellite variation was lower in both Scandinavian populations compared with the other European populations and mitochondrial
DNA variation was especially low in the Swedish population where only one unique haplotype was observed. Loss of microsatellite
alleles was demonstrated by low M ratios in all populations except the Hungarian. M ratios’ were especially low in the Scandinavian
populations, indicating additional or more severe bottlenecks. Heterozygosity excess compared with the expectation from the
number of observed microsatellite alleles suggested a recent bottleneck of low severity in the Norwegian population. Hierarchical
Bayesian coalescent analyses consistently yielded estimates of a large ancestral and a small current population size in all
investigated European populations and suggested the onset of population decline to be between 5,000 and 10,000 years ago,
which coincide well with postglacial colonisation. 相似文献
6.
Species introductions provide a rare opportunity to study rapid evolutionary and genetic processes in natural systems, often under novel environmental pressures. Few empirical studies have been able to characterize genetic founder effects associated with demographic bottlenecks at the earliest stages of species introductions. This study utilizes prior mitochondrial DNA information which identifies the putative source population for a recently established ( c . 7 years between import and sampling) species introduction. We investigated the evidence for a founder effect in a highly successful introduction of a Puerto Rican Anolis species that has established itself on Dominica to the localized exclusion of the native, endemic anole. Five highly polymorphic microsatellite loci were used to explore the partitioning of genetic diversity within and between native source, native nonsource, and introduced populations of Anolis cristatellus . Group comparisons reveal significantly lower allelic richness and expected heterozygosity in introduced populations compared to native populations; however, tests for heterozygosity excess relative to allelic richness failed to provide consistent evidence for a founder effect within introduced populations. Significant levels of within-population genetic variation were present in both native and introduced populations. We suggest that aspects of the reproductive ecology of Anolis (high fecundity, sperm storage and multiple paternity) offer an important mechanism by which genetic variation may be maintained following demographic bottlenecks and founder events in some squamate taxa. 相似文献
7.
R. S. A. Pickles J. J. Groombridge V. D. Zambrana Rojas P. Van Damme D. Gottelli C. V. Ariani W. C. Jordan 《Conservation Genetics》2012,13(1):235-245
We assessed levels of genetic diversity and investigated patterns of population structure in three remnant populations of
the endangered giant otter, Pteronura brasiliensis, using microsatellite loci. All populations displayed moderate to low levels of heterozygosity and allelic richness (H
O
0.56–0.57, A
R
4.00–5.15) and effective population sizes were low (N
E
10.8–54) although only the Iténez population exhibited the signature of a genetic bottleneck. Population structure analyses
revealed a pattern in which the populations of the Upper Amazon, Orinoco and Essequibo drainages comprised partially differentiated
segments of a northern South American metapopulation, whereas the population of the Iténez appeared isolated. The observed
patterns are congruent with previous mitochondrial DNA analysis which suggested the Iténez and northern South American groups
constitute two evolutionary significant units. The results presented here should be considered in planning future policies
aiming to manage the recovery of the giant otter across its range. 相似文献
8.
Asymmetric gene flow and the evolutionary maintenance of genetic diversity
in small,peripheral Atlantic salmon populations 总被引:4,自引:4,他引:0
Small populations may be expected to harbour less genetic variation than large populations, but the relation between census
size (N), effective population size (N
e), and genetic diversity is not well understood. We compared microsatellite variation in four small peripheral Atlantic salmon
populations from the Iberian peninsula and three larger populations from Scotland to test whether genetic diversity was related
to population size. We also examined the historical decline of one Iberian population over a 50-year period using archival
scales in order to test whether a marked reduction in abundance was accompanied by a decrease in genetic diversity. Estimates
of effective population size (N
e) calculated by three temporal methods were consistently low in Iberian populations, ranging from 12 to 31 individuals per
generation considering migration, and from 38 to 175 individuals per generation if they were regarded as closed populations.
Corresponding N
e/N ratios varied from 0.02 to 0.04 assuming migration (mean=0.03) and from 0.04 to 0.18 (mean=0.10) assuming closed populations.
Population bottlenecks, inferred from the excess of heterozygosity in relation to allelic diversity, were detected in all
four Iberian populations, particularly in those year classes derived from a smaller number of returning adults. However, despite
their small size and declining status, Iberian populations continue to display relatively high levels of heterozygosity and
allelic richness, similar to those found in larger Scottish populations. Furthermore, in the R. Asón no evidence was found
for a historical loss of genetic diversity despite a marked decline in abundance during the last five decades. Thus, our results
point to two familiar paradigms in salmonid conservation: (1)␣endangered populations can maintain relatively high levels of
genetic variation despite their small size, and (2) marked population declines may not necessarily result in a significant
loss of genetic diversity. Although there are several explanations for such results, microsatellite data and physical tagging
suggest that high levels of dispersal and asymmetric gene flow have probably helped to maintain genetic diversity in these
peripheral populations, and thus to avoid the negative consequences of inbreeding. 相似文献
9.
Documented demographic bottlenecks resultingfrom introductions of the dice snake to severallakes in Switzerland provide a rare opportunityto study the effect of serial bottlenecks onthe genetic properties of Natrixtessellata populations. We investigated twointroduced populations using informationderived from eight microsatellite markers. Bothintroduced populations had significantlyreduced levels of allelic diversity relative tonon-bottlenecked populations. The severity ofthe bottlenecks was underlined by thesignificant reduction in observed and expectedheterozygosity. The loss of allelic diversityand observed heterozygosity was stronger in theserially bottlenecked population than in thepopulation that was bottlenecked only once.From previous studies, scale anomalies wereknown to be more common in introducedpopulations relative to native populations. Weinvestigated whether the higher occurrence ofscale anomalies in introduced populations isassociated with individual heterozygosity andmean genomic diversity d
2. We founda significant relationship between theoccurrence of scale anomalies and individualheterozygosity but no significant relationshipbetween scale anomalies and the microsatellitespecific measurement, d
2, was found.Because of their known history, introducedpopulations in Switzerland may serve as a modelto demonstrate the effect of severe populationbottlenecks on genetic variability anddevelopmental stability in N. tessellata.The results therefore help to device strategiesfor the management and protection of endangerednatural N. tessellata populations. 相似文献
10.
Jacob Höglund Jobs Karl Larsson Hugh A. H. Jansman Gernot Segelbacher 《Conservation Genetics》2007,8(1):239-243
We studied microsatellite genetic variation in 14 different geographic populations of black grouse (Tetrao tetrix) across the European range. Populations were grouped in three different fragmentation categories: isolated, contiguous and
continuous, respectively. Genetic diversity, measured as observed heterozygosity (H
O), expected heterozygosity (H
E) and allelic richness, were lower in isolated populations as compared to the other two categories that did not differ amongst
one another. These results imply that lowered genetic variability in black grouse populations is negatively affected by population
isolation. Our results suggest that the connectivity of small and isolated populations in Western Europe should be improved
or else these face an increased risk of extinction due to genetic and demographic stochasticity. 相似文献
11.
The objectives of this study were to assess the level of genetic variability and population differentiation within captive populations of an endangered large mammal, Baird's tapir (Tapirus bairdii). We genotyped 37 captive animals from North American (NA) and Central American (CA) zoos and conservation ranches using six polymorphic microsatellite loci. Standard indices of genetic variability (allelic richness and diversity, and heterozygosity) were estimated and compared between captive populations, and between captive and wild population samples. In addition, we evaluated levels of population differentiation using Weir and Cockerham's version of Wright's F-statistics. The results indicate that the NA and CA captive populations of Baird's tapirs have retained levels of genetic variability similar to that measured in a wild population. However, inbreeding coefficients estimated from the molecular data indicate that the CA captive population is at increased risk of losing genetic variability due to inbreeding. Despite this, estimated levels of population differentiation indicate limited divergence of the CA captive population from the wild population. Careful management appears to have kept inbreeding coefficients low in the NA captive population; however, population differentiation levels indicate that the NA population has experienced increased divergence from wild populations due to a founder effect and isolation. Based on these results, we conclude that intermittent exchanges of Baird's tapirs between the NA and CA captive populations will benefit both populations by increasing genetic variability and effective population size, while reducing inbreeding and divergence from wild populations. Zoo Biol 23:521–531, 2004. © 2004 Wiley-Liss, Inc. 相似文献
12.
Nikoleta Karaiskou Maria Lappa Stefanos Kalomoiris George Oikonomidis Chariklia Psaltopoulou Theodore J. Abatzopoulos Costas Triantaphyllidis Alexander Triantafyllidis 《Conservation Genetics》2011,12(5):1299-1311
The ability to detect genetic differences both in space and time is crucial for conserving genetic variation. It can reveal
genetic diversity and genetic composition changes of declining native populations that are supported through stocking with
captive bred individuals. The present study was designed to analyse the temporal stability of a declining common carp (Cyprinus carpio) population from Lake Volvi (North Greece). Polymorphism was evaluated using seven microsatellite loci at two sampling time
points (separated by 12 years). The genetic variability of four additional populations (from two rivers and two lakes) in
Northern Greece was also investigated for comparison. Heterozygosity values (0.692–0.868) and allelic richness (8.530–11.148)
were high for all studied populations and comparable to other European populations. However, the analysis of temporal common
carp samples from Lake Volvi revealed a significant change in their genetic composition and admixture analysis demonstrated
significant introgression of stocked individuals into the native population. Both temporal and point estimate methods revealed
low effective size (Ne = 61–171.3) for this population, possibly a result of an ancient genetic bottleneck that led to population decline and/or
recent anthropogenic interventions. This low Ne has rendered the native population vulnerable to alteration of its genetic composition. Our study demonstrates that enhancement
programs should be applied cautiously, especially for small populations. Moreover, it underlines the need for temporal analyses,
which may contribute to the evaluation of previous management policies and to future decision making. 相似文献
13.
Bradley J. Cosentino Robert L. Schooley Brandon T. Bestelmeyer Alison J. McCarthy Kevin Sierzega 《Molecular ecology》2015,24(24):6120-6133
Genetic founder effects are often expected when animals colonize restored habitat in fragmented landscapes, but empirical data on genetic responses to restoration are limited. We examined the genetic response of banner‐tailed kangaroo rats (Dipodomys spectabilis) to landscape‐scale grassland restoration in the Chihuahuan Desert of New Mexico, USA. Dipodomys spectabilis is a grassland specialist and keystone species. At sites treated with herbicide to remove shrubs, colonization by D. spectabilis is slow and populations persist at low density for ≥10 years (≥6 generations). Persistence at low density and low gene flow may cause strong founder effects. We compared genetic structure of D. spectabilis populations between treated sites and remnant grasslands, and we examined how the genetic response to restoration depended on treatment age, area, and connectivity to source populations. Allelic richness and heterozygosity were similar between treated sites and remnant grasslands. Allelic richness at treated sites was greatest early in the restoration trajectory, and genetic divergence did not differ between recently colonized and established populations. These results indicated that founder effects during colonization of treated sites were weak or absent. Moreover, our results suggested founder effects were not mitigated by treatment area or connectivity. Dispersal is negatively density‐dependent in D. spectabilis, and we hypothesize that high gene flow may occur early in the restoration trajectory when density is low. Our study shows genetic diversity can be recovered more rapidly than demographic components of populations after habitat restoration and that founder effects are not inevitable for animals colonizing restored habitat in fragmented landscapes. 相似文献
14.
Due to the importance of preserving the genetic integrity of populations, strategies to restore damaged coral reefs should
attempt to retain the allelic diversity of the disturbed population; however, genetic diversity estimates are not available
for most coral populations. To provide a generalized estimate of genetic diversity (in terms of allelic richness) of scleractinian
coral populations, the literature was surveyed for studies describing the genetic structure of coral populations using microsatellites.
The mean number of alleles per locus across 72 surveyed scleractinian coral populations was 8.27 (±0.75 SE). In addition,
population genetic datasets from four species (Acropora palmata, Montastraea cavernosa, Montastraea faveolata and Pocillopora damicornis) were analyzed to assess the minimum number of donor colonies required to retain specific proportions of the genetic diversity
of the population. Rarefaction analysis of the population genetic datasets indicated that using 10 donor colonies randomly
sampled from the original population would retain >50% of the allelic diversity, while 35 colonies would retain >90% of the
original diversity. In general, scleractinian coral populations are genetically diverse and restoration methods utilizing
few clonal genotypes to re-populate a reef will diminish the genetic integrity of the population. Coral restoration strategies
using 10–35 randomly selected local donor colonies will retain at least 50–90% of the genetic diversity of the original population.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
15.
Paul L. Leberg 《Evolution; international journal of organic evolution》1992,46(2):477-494
Low levels of allozyme heterozygosity in populations are often attributed to previous population bottlenecks; however, few experiments have examined the relationship between heterozygosity and bottlenecks under natural conditions. The composition and number of founders of 55 experimental populations of the eastern mosquitofish (Gambusia holbrooki), maintained under simulated field conditions, were manipulated to examine the effects of bottlenecks on three components of allozyme diversity. Correlations between observed and expected values of allozyme heterozygosity, proportions of polymorphic loci, and numbers of alleles per locus were 0.423, 0.602, and 0.772, respectively. The numbers of polymorphic loci and of alleles per locus were more sensitive indicators of differences in genetic diversity between the pre-bottleneck and post-bottleneck populations than was multiple-locus heterozygosity. In many populations, single- and multiple-locus heterozygosity actually increased as a result of the founder event. The weak relationship between a population's heterozygosity and the number and composition of its founders resulted from an increase in the variance of heterozygosity due to drift of allele frequencies. There was little evidence that selection influenced the loss of allozyme variation. When it is not possible to estimate heterozygosity at a large number of polymorphic loci, allozyme surveys attempting to detect founder events and other types of bottlenecks should focus on levels of locus polymorphism and allelic diversity rather than on heterozygosity. 相似文献
16.
Genetic diversity of a successful colonizer: isolated populations of Metrioptera roeselii regain variation at an unusually rapid rate 下载免费PDF全文
Newly founded isolated populations need to overcome detrimental effects of low genetic diversity. The establishment success of a population may therefore depend on various mechanisms such as assortative mating, purging of deleterious alleles, creation of new mutations and/or repeated inflow of new genotypes to reduce the effects of inbreeding and further loss of genetic variation. We compared the level of genetic variation in introduced populations of an insect species (Metrioptera roeselii) far beyond its natural distribution with levels found in their respective founder populations and coupled the data with timing since establishment. This allowed us to analyze if the introduced populations showed signs of temporal changes in genetic variation and have made it possible to evaluate underlying mechanisms. For this, we used neutral genetic markers, seven microsatellite loci and a 676–bp‐long sequence of the mtDNA COI gene. All tested indices (allelic richness, unbiased expected heterozygosity, effective size, haplotype diversity, and nucleotide diversity) except inbreeding coefficient had significantly higher values in populations within the founding populations inside the continuous area of the species distribution compared with the introduced populations. A logarithmic model showed a significant correlation of both allelic richness and unbiased expected heterozygosity with age of the isolated populations. Considering the species' inferred colonization history and likely introduction pathways, we suggest that multiple introductions are the main mechanism behind the temporal pattern observed. However, we argue that influences of assortative mating, directional selection, and effects of an exceptional high intrapopulation mutation rate may have impacts. The ability to regain genetic diversity at this level may be one of the main reasons why M. roeselii successfully continue to colonize northern Europe. 相似文献
17.
Warangkana Prakoon Suriyan Tunkijjanukij Thuy T. T. Nguyen Uthairat Na-Nakorn 《Marine biotechnology (New York, N.Y.)》2010,12(5):506-515
The culture of green mussel (Perna viridis) in the Gulf of Thailand depends on natural spat which are believed to come from spawning grounds adjacent to major river
mouths. In the present paper, genetic diversity of spatial and temporal populations of green mussel in the Gulf of Thailand
was investigated using five microsatellite loci. The results showed moderate genetic variation of all 11 populations (averaged
number of alleles per locus, A = 10.4–12.2; effective number of alleles per locus, A
e = 5.36–6.59; mean allelic richness, A
r = 10.23–12.06; observed heterozygosity, H
o = 0.52–0.63, and expected heterozygosity, H
e = 0.66–0.73) without significant differences among populations. No sign of bottleneck or genetic disequilibrium was observed.
Genetic differentiation among spatial populations was low (F
ST = 0.0046, CI0.95 = 0.0020–0.0083 for the samples collected in January, 2007, and F
ST = 0.0088, CI0.95 = 0.0010–0.0162 for the samples collected in July, 2007) while temporal variation was significant as revealed by the analysis
of molecular variance. Multidimensional scaling separated temporal population groups with minor exception. The assignment
test revealed that most of the recruits were from other populations. 相似文献
18.
Biological invasions offer excellent systems to study the evolutionary processes involved in introductions of species to new
ranges. Molecular markers can reveal invasion histories and the effects of introductions on amounts and structuring of genetic
variation. We used five polymorphic microsatellite loci to elucidate genetic diversity and population structure between native
range and introduced range populations of a prominent North American rangeland weed, Centaurea diffusa (Asteraceae). We found that the total number of alleles and the number of private alleles was slightly higher in the native
Eurasian range, and that allelic richness did not differ between the ranges, indicating overall levels of diversity were similar
in Eurasia and North America. It therefore seems unlikely that this invasion has been affected by genetic bottlenecks or founder
effects. Indeed, results of assignment tests suggest that multiple introductions have contributed to North America’s C. diffusa invasion. Additionally, assignment tests show that both Eurasian and North American sites had a strong pattern of mixed genetic
ancestry. This mixed assignment corresponded to a lack of geographic population structure among Eurasian samples. The lack
of population structure in the native range conflicts with general expectations and findings to date for invasion genetics,
and cautions that even species’ native ranges may show signs of recent ecological upheaval. Despite the mixed assignments,
North American samples showed strong population structure, suggesting that the invasion has been characterized by long-range
dispersal of genetically distinct propagules across the introduced range. 相似文献
19.
Levels of genetic variability at 12 microsatellite loci and 19 single nucleotide polymorphisms in mitochondrial DNA were studied
in four farm strains and four wild populations of Atlantic salmon. Within populations, the farm strains showed significantly
lower allelic richness and expected heterozygosity than wild populations at the 12 microsatellite loci, but a significantly
higher genetic variability with respect to observed number of haplotypes and haplotype diversity in mtDNA. Significant differences
in allele- and haplotype-frequencies were observed between farm strains and wild populations, as well as between different
farm strains and between different wild populations. The large genetic differentiation at mitochondrial DNA between wild populations
(FST = 0.24), suggests that the farm strains attained a high mitochondrial genetic variability when created from different wild
populations seven generations ago. A large proportion of this variability remains despite an expected lower effective population
size for mitochondrial than nuclear DNA. This is best explained by the particular mating schemes in the breeding programmes,
with 2–4 females per male. Our observations suggest that for some genetic polymorphisms farm populations might currently hold
equal or higher genetic variability than wild populations, but lower overall genetic variability. In the short-term, genetic
interactions between escaped farm salmon and wild salmon might increase genetic variability in wild populations, for some,
but not most, genetic polymorphisms. In the long term, further losses of genetic variability in farm populations are expected
for all genetic polymorphisms, and genetic variability in wild populations will be reduced if escapes of farm salmon continue. 相似文献
20.
Sharp declines in population size, known as genetic bottlenecks, increase the level of inbreeding and reduce genetic diversity
threatening population sustainability in both short- and long-term. We evaluated the presence, severity and approximate time
of bottlenecks in 34 European grayling (Thymallus thymallus) populations covering the majority of the species distribution using microsatellite markers. We identified footprints of
population decline in all grayling populations using the M ratio test. In contrast to earlier simulation studies assuming isolated populations, forward simulations allowing low levels
of migration demonstrated that bottleneck footprints measured using the M ratio can persist within small populations much longer (up to thousands of generations) than previously anticipated. Using
a coalescence approach, the beginning of population reduction was dated back to 1,000–10,000 years ago which suggests that
the extremely low M ratio in European grayling is most likely caused by the last glaciation and subsequent post-glacial recolonization processes.
In contrast to the M ratio, two alternative methods for bottleneck detection identified more recent bottlenecks in six populations and thus, from
a conservation perspective, these populations warrant future monitoring. Based on a single time-point analysis using approximate
Bayesian computation methodology, all grayling populations exhibited very small effective population sizes with the majority
of N
e estimates below 50. Taken together, our results demonstrate the predominate role of genetic drift in European grayling populations
in the short term but also emphasize the importance of gene flow counteracting the effects of genetic drift and loss of variation
over longer evolutionary timescales. 相似文献