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1.
The spatial and temporal genetic structure of brown trout populations from three small tributaries of Lake Hald, Denmark,
was studied using analysis of variation at eight microsatellite loci. From two of the populations temporal samples were available,
separated by up to 13 years (3.7 generations). Significant genetic differentiation was observed among all samples, however,
hierarchical analysis of molecular variance (AMOVA) showed that differentiation among populations accounted for a non-significant
amount of the genetic differentiation, whereas differentiation among temporal samples within populations was highly significant
(0.0244, P<0.001). Estimates of effective population size (N
e) using a maximum-likelihood based implementation of the temporal method, yielded small values (N
e ranging from 33 to 79). When a model was applied that allows for migration among populations, N
e estimates were even lower (24–54), and migration rates were suggested to be high (0.13–0.36). All samples displayed a clear
signal of a recent bottleneck, probably stemming from a period of unfavourable conditions due to organic pollution in the
1970–1980’s. By comparison to other estimates of N
e in brown trout, Lake Hald trout represent a system of small populations linked by extensive gene flow, whereas other populations
in larger rivers exhibit much higher N
e values and experience lower levels of immigration. We suggest that management considerations for systems like Lake Hald brown
trout should focus both on a regional scale and at the level of individual populations, as the future persistence of populations
depends both on maintaining individual populations and ensuring sufficient migration links among these populations. 相似文献
2.
Sanne Boessenkool Bastiaan Star Philip J. Seddon Jonathan M. Waters 《Conservation Genetics》2010,11(2):539-546
There is an increasing awareness that the long-term viability of endemic island populations is negatively affected by genetic
factors associated with population bottlenecks and/or persistence at small population size. Here we use contemporary samples
and historic museum specimens (collected 1888–1938) to estimate the effective population size (N
e) for the endangered yellow-eyed penguin (Megadyptes antipodes) in South Island, New Zealand, and evaluate the genetic concern for this iconic species. The South Island population of M. antipodes—constituting almost half of the species’ census size—is thought to be descended from a small number of founders that reached
New Zealand just a few hundred years ago. Despite intensive conservation measures, this population has shown dramatic fluctuations
in size over recent decades. We compare estimates of the harmonic mean N
e for this population, obtained using one moment and three likelihood based-temporal methods, including one method that simultaneously
estimates migration rate. Evaluation of the N
e estimates reveals a harmonic mean N
e in the low hundreds. Additionally, the inferred low immigration rates (m = 0.003) agree well with contemporary migration rate estimates between the South Island and subantarctic populations of M. antipodes. The low N
e of South Island M. antipodes is likely affected by strong fluctuations in population size, and high variance in reproductive success. These results show
that genetic concerns for this population are valid and that the long-term viability of this species may be compromised by
reduced adaptive potential. 相似文献
3.
Genetic neighbourhood and effective population size (N
e) are critical factors when determining the potential survival of threatened species. Carnivores have intrinsically small effective numbers, because, as top predators, they show low densities. The European mink, Mustela lutreola, is one of the most endangered carnivores in the world and has suffered continual decline and local extinctions. The genetic neighbourhood, area within which adults could randomly mate, averaged N
a = 31.7 km diameter, allowing that population size within the neighbourhood area only ranged from N
b = 6.1 to 22.8 animals. Although the population size was assessed in one of the main mink populations in the world, this neighbourhood size is far below the values regarded as critical in literature. However, in contrast with recent propositions, the ratio N
e
/N only ranged between 0.09 and 0.19, estimates close to the average recognised by Frankham [(1995) Genetic Research 66: 95–107] for wildlife populations. In the context of the challenge to conserve this endangered carnivore, the studied neighbourhood provided crucial information suggesting both a low neighbourhood size and severe disturbance of breeding exchanges, emphasising the dramatically threatened status of the European mink. 相似文献
4.
Helle Tessand Baalsrud Bernt‐Erik Sæther Ingerid Julie Hagen Ane Marlene Myhre Thor Harald Ringsby Henrik Pärn Henrik Jensen 《Molecular ecology》2014,23(11):2653-2668
Effective population size (Ne) is a key parameter to understand evolutionary processes and the viability of endangered populations as it determines the rate of genetic drift and inbreeding. Low Ne can lead to inbreeding depression and reduced population adaptability. In this study, we estimated contemporary Ne using genetic estimators (LDNE, ONeSAMP, MLNE and CoNe) as well as a demographic estimator in a natural insular house sparrow metapopulation. We investigated whether population characteristics (population size, sex ratio, immigration rate, variance in population size and population growth rate) explained variation within and among populations in the ratio of effective to census population size (Ne/Nc). In general, Ne/Nc ratios increased with immigration rates. Genetic Ne was much larger than demographic Ne, probably due to a greater effect of immigration on genetic than demographic processes in local populations. Moreover, although estimates of genetic Ne seemed to track Nc quite well, the genetic Ne‐estimates were often larger than Nc within populations. Estimates of genetic Ne for the metapopulation were however within the expected range (<Nc). Our results suggest that in fragmented populations, even low levels of gene flow may have important consequences for the interpretation of genetic estimates of Ne. Consequently, further studies are needed to understand how Ne estimated in local populations or the total metapopulation relates to actual rates of genetic drift and inbreeding. 相似文献
5.
Population subdivision due to habitat loss and modification, exploitation of wild populations and altered spatial population
dynamics is of increasing concern in nature. Detecting population fragmentation is therefore crucial for conservation management.
Using computer simulations, we show that a single sample estimator of N
e based on linkage disequilibrium is a highly sensitive and promising indicator of recent population fragmentation and bottlenecks,
even with some continued gene flow. For example, fragmentation of a panmictic population of N
e = 1,000 into demes of N
e = 100 can be detected with high probability after a single generation when estimates from this method are compared to prefragmentation
estimates, given data for ~20 microsatellite loci in samples of 50 individuals. We consider a range of loci (10–40) and individuals
(25–100) typical of current studies of natural populations and show that increasing the number of loci gives nearly the same
increase in precision as increasing the number of individuals sampled. We also evaluated effects of incomplete fragmentation
and found this N
e-reduction signal is still apparent in the presence of considerable migration (m ~ 0.10–0.25). Single-sample genetic estimates of N
e thus show considerable promise for early detection of population fragmentation and decline. 相似文献
6.
Andrew R. Whiteley Kim Hastings John K. Wenburg Chris A. Frissell Jamie C. Martin Fred W. Allendorf 《Conservation Genetics》2010,11(5):1929-1943
Following glacial recession in southeast Alaska, waterfalls created by isostatic rebound have isolated numerous replicate
populations of coastal cutthroat trout (Oncorhynchus clarkii clarkii) in short coastal streams. These replicate isolated populations offer an unusual opportunity to examine factors associated
with the maintenance of genetic diversity. We used eight microsatellites to examine genetic variation within and differentiation
among 12 population pairs sampled from above and below these natural migration barriers. Geological evidence indicated that
the above-barrier populations have been isolated for 8,000–12,500 years. Genetic differentiation among below-barrier populations
(F
ST = 0.10, 95% C.I. 0.08–0.12) was similar to a previous study of more southern populations of this species. Above-barrier populations
were highly differentiated from adjacent below-barrier populations (mean pairwise F
ST = 0.28; SD 0.18) and multiple lines of evidence were consistent with asymmetric downstream gene flow that varied among streams.
Each above-barrier population had reduced within-population genetic variation when compared to the adjacent below-barrier
population. Within-population genetic diversity was significantly correlated with the amount of available habitat in above-barrier
sites. Increased genetic differentiation of above-barrier populations with lower genetic diversity suggests that genetic drift
has been the primary cause of genetic divergence. Long-term estimates of N
e based on loss of heterozygosity over the time since isolation were large (3,170; range 1,077–7,606) and established an upper
limit for N
e if drift were the only evolutionary process responsible for loss of genetic diversity. However, it is likely that a combination
of mutation, selection, and gene flow have also contributed to the genetic diversity of above-barrier populations. Contemporary
above-barrier N
e estimates were much smaller than long-term N
e estimates, not correlated with within-population genetic diversity, and not consistent with the amount of genetic variation
retained, given the approximate 10,000-year period of isolation. The populations isolated by waterfalls in this study that
occur in larger stream networks have retained substantial genetic variation, which suggests that the amount of habitat in
headwater streams is an important consideration for maintaining the evolutionary potential of isolated populations. 相似文献
7.
Marnie H. Demandt 《Conservation Genetics》2010,11(1):249-255
Genetic drift, together with natural selection and gene flow, affects genetic variation and is the major source of changes
in allele frequencies in small and isolated populations. Temporal shifts in allele frequencies at five polymorphic loci were
used to estimate the amount of genetic drift in an isolated population of perch (Perca fluviatilis L.) and roach (Rutilus rutilus L.). Here, I used the populations from the Biotest basin at Forsmark, Sweden, to investigate genetic diversity between 1977
and 2000, during which time the population can be considered to be totally isolated from other populations. Microsatellite
data reveal stable levels of gene diversity over time for both species. Estimates of genetic differentiation (F
ST) showed a significant divergence between 1977 and 2000 for both perch and roach. A positive correlation between genetic distance
and time was found (Mantel test, perch: r = 0.724, P = 0.0112; roach: r = 0.59, P = 0.036). Estimates of effective population size (N
e) differed with a factor six between two different estimators (NeEstimator and TempoFS) applying the temporal method. Ratios
of N
e/N ranged between 10−2 and 10−3, values normally found in marine species. Despite low N
e the populations have not lost their evolutionary potential due to drift. But two decades of isolation have lead to isolation
by time for populations of perch and roach, respectively. 相似文献
8.
Andrew J. Gregory Robb S. A. Kaler Thomas J. Prebyl Brett K. Sandercock Samantha M. Wisely 《Conservation Genetics》2012,13(2):465-474
Island populations and populations established by reintroductions are prone to extinction, in part because they are vulnerable
to deterministic and stochastic phenomena associated with geographic isolation and small population size. As population size
declines, reduced genetic diversity can result in decreased fitness and reduced adaptive potential, which may hinder short-
or long-term population viability. We used 32 microsatellite markers to investigate the conservation genetics of a newly established
population of Evermann’s Rock Ptarmigan (Lagopus muta evermanni) at Agattu Island, in the western Aleutian Archipelago, Alaska. We found low genetic diversity (observed heterozygosity = 0.41,
allelic richness = 2.2) and a small effective population size (N
e
= 28.6), but a relatively large N
e
/N ratio = 0.55, which was attributed to multiple paternity in 80% of the broods and low reproductive skew among males (λ = 0.29).
Moreover, successful breeding pairs were less related to each other than random male–female pairs. For conservation efforts
based on reintroductions, a mating system with high rates of multiple paternity may facilitate retention of genetic diversity,
thereby reducing the potential for inbreeding in small or isolated populations. Our results underscore the importance of quantifying
genetic diversity and understanding the breeding behavior of translocated populations. 相似文献
9.
Satu Lampila Laura Kvist Ralf Wistbacka Markku Orell 《European Journal of Wildlife Research》2009,55(4):397-406
Siberian flying squirrel (Pteromys volans) has declined in Finland and it is considered an endangered species. We studied microsatellite variation in four flying squirrel
populations in a fragmented landscape in Finland to determine the amount of gene flow and genetic diversity in the populations.
Demographic data from these areas suggest that the populations are declining. All the populations are significantly differentiated
(F
ST = 0.23). The most notable result is the high degree of differentiation between two adjacent populations (F
ST = 0.11) and low genetic variability (number of alleles 3.0) in one of the populations. These findings suggest problems in
dispersal and possible fragmentation effects in the landscape where only 10–20% of habitat favorable for the flying squirrel
is left. Conservation ensuring dispersal should be urgently considered. Future studies should concentrate on the modeling
of the population viability and on the effects of inbreeding in these small populations.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
10.
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
11.
Jeffrey B. Olsen Andrew P. Kinziger John K. Wenburg Cara J. Lewis Catherine T. Phillips Kenneth G. Ostrand 《Conservation Genetics》2016,17(6):1393-1404
The endangered fountain darter Etheostoma fonticola is found only in the Comal and San Marcos rivers in the Guadalupe River basin in central Texas, USA. Comal River fountain darters were believed to be extirpated following a severe drought in the 1950s and were reintroduced in the early 1970s using 457 darters from the San Marcos River. In this study we used 23 microsatellite loci to describe and evaluate the genetic diversity, population structure and effective population size (N e) of fountain darters. We also evaluated the genetic effect of the Comal River reintroduction and the influence of low-head dams (dams) on dispersal in both rivers. Bayesian analysis of individual genotypes and Analysis of Molecular Variation supported two distinct populations concordant with the two rivers. Estimates of N e were much smaller (<10 %) than census size (N c) in both rivers but did not indicate the populations are at risk of an immediate and rapid loss of genetic diversity. Coalescent-based estimates of the genetically effective number of founders (Nf) for the Comal River averaged about 49 darters and, together with the indices of genetic diversity and the bottleneck test (heterozygosity excess) results, were consistent with a founder event following the reintroduction in the Comal River. Finally, our results regarding the influence of dams on fountain darter dispersal were equivocal and did not support a conclusion. We recommend this issue be examined further as part of the fountain darter recovery program. 相似文献
12.
Ian J. Wang Jarrett R. Johnson Benjamin B. Johnson H. Bradley Shaffer 《Conservation Genetics》2011,12(4):911-920
Maintaining genetic diversity and population viability in endangered and threatened species is a primary concern of conservation
biology. Genetic diversity depends on population connectivity and effective population size (Ne), both of which are often compromised in endangered taxa. While the importance of population connectivity and gene flow has
been well studied, investigating effective population sizes in natural systems has received far less attention. However, Ne plays a prominent role in the maintenance of genetic diversity, the prevention of inbreeding depression, and in determining
the probability of population persistence. In this study, we examined the relationship between breeding pond characteristics
and Ne in the endangered California tiger salamander, Ambystoma californiense. We sampled 203 individuals from 10 breeding ponds on a local landscape, and used 11 polymorphic microsatellite loci to quantify
genetic structure, gene flow, and effective population sizes. We also measured the areas of each pond using satellite imagery
and classified ponds as either hydrologically-modified perennial ponds or naturally occurring vernal pools, the latter of
which constitute the natural breeding habitat for A. californiense. We found no correlation between pond area and heterozygosity or allelic diversity, but we identified a strong positive relationship
between breeding pond area and Ne, particularly for vernal pools. Our results provide some of the first empirical evidence that variation in breeding habitat
can be associated with differences in Ne and suggest that a more complete understanding of the environmental features that influence Ne is an important component of conservation genetics and management. 相似文献
13.
Berchemiella wilsonii var. pubipetiolata (Rhamnaceae) is an endangered plant with only four remnant populations in eastern China. Population genetic information is
essential for understanding population history and formulating conservation strategies for this species. Thirteen microsatellite
loci were used to investigate genetic variation and population structure of the four remnant populations. Moderate levels
of expected heterozygosity (H
E = 0.466–0.543) and low allelic diversity (A = 3.1–3.6 and A
R = 2.2–2.4, respectively) were observed within populations. Bottleneck tests found three out of four populations to deviate
from mutation-drift equilibrium under the two-phase model (TPM), suggesting a recent population decline, which is congruent
with known demographic history. The evolutionary history of the species seems dominated by genetic drift rather than gene
flow. Low historical gene flow was inferred from several different approaches and N
m ranged from 0.582 by the private allele method to 0.783 by the coalescent method. Contemporary gene flow was also found to
be even lower for only one first generation migrant was detected with individual-based assignment analysis. Restricted pollen
and seed dispersal as well as a recent decline in population size associated with habitat fragmentation may have contributed
to low levels of historical and contemporary gene flow, and resulted in a high genetic differentiation. Under this scenario,
Berchemiella wilsonii var. pubipetiolata populations are expected to display more pronounced population genetic structure in the future as a result of increased inbreeding
and genetic drift. 相似文献
14.
Genome‐wide linkage disequilibrium and past effective population size in three Korean cattle breeds
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P. Sudrajad D. W. Seo T. J. Choi B. H. Park S. H. Roh W. Y. Jung S. S. Lee J. H. Lee S. Kim S. H. Lee 《Animal genetics》2017,48(1):85-89
The routine collection and use of genomic data are useful for effectively managing breeding programs for endangered populations. Linkage disequilibrium (LD) using high‐density DNA markers has been widely used to determine population structures and predict the genomic regions that are associated with economic traits in beef cattle. The extent of LD also provides information about historical events, including past effective population size (Ne), and it allows inferences on the genetic diversity of breeds. The objective of this study was to estimate the LD and Ne in three Korean cattle breeds that are genetically similar but have different coat colors (Brown, Brindle and Jeju Black Hanwoo). Brindle and Jeju Black are endangered breeds with small populations, whereas Brown Hanwoo is the main breeding population in Korea. DNA samples from these cattle breeds were genotyped using the Illumina BovineSNP50 Bead Chip. We examined 13 cattle breeds, including European taurines, African taurines and indicines, and hybrids to compare their LD values. Brown Hanwoo consistently had the lowest mean LD compared to Jeju Black, Brindle and the other 13 cattle breeds (0.13, 0.19, 0.21 and 0.15–0.22 respectively). The high LD values of Brindle and Jeju Black contributed to small Ne values (53 and 60 respectively), which were distinct from that of Brown Hanwoo (531) for 11 generations ago. The differences in LD and Ne for each breed reflect the breeding strategy applied. The Ne for these endangered cattle breeds remain low; thus, effort is needed to bring them back to a sustainable tract. 相似文献
15.
Yaisel Juan Borrell David Bernardo Gloria Blanco Emilia Vázquez José Antonio Sánchez 《Conservation Genetics》2008,9(4):807-819
Rivers in Asturias (northern Spain) constitute the southern limit of the distribution of Atlantic salmon (Salmo salar L.) in Europe, a biological resource facing one of the more serious challenges for conservation today. In this work, eight microsatellite
loci have been used to analyse samples collected in 1993 and 1999 from four Asturian rivers (Esva, Narcea, Sella, and Cares),
obtaining information about the temporal and the spatial genetic variation in these populations and, in addition, estimations
of their effective population sizes. The temporal analysis revealed a general decrease in all the estimated genetic variability
parameters when samples from 1993 (mean A
(1993) = 6.47, mean H
O(1993) = 0.472, mean H
E(1993) = 0.530) were compared with those obtained in 1999 (mean A
(1999) = 6.16, mean H
O(1999) = 0.460, mean H
E(1999) = 0.490). This reduction was particularly notable for the case of the Esva river. Our results pointed to a pattern of spatial
genetic differentiation inside the Asturian region (F
ST (1993) = 0.016 P < 0.01; F
ST (1999) = 0.023 P < 0.01). Using the standard Temporal Method we found estimates of N
e^
(Esva) = 75.1 (33.2–267.2); N
e^
(Cares) = 96.6 (40.0–507.5), N
e^
(Sella) = 106.5 (39.1–9396.4) and N
e^
(Narcea) = 113.9 (42.0–3693.3). The use of likelihood-based methods for the N
e^ estimations improved the results (smaller CIs) for the Esva and Cares rivers (N
e^
(Esva) = 63.9 (32.3–165.3); N
e^
(Cares) = 76.4 (38.8–202.0) using a Maximum likelihood approach) and suggested the presence of larger populations for the Sella and
Narcea rivers (N
e^≈200). These results showed that the Asturian Atlantic salmon populations (in particular Esva and Cares river populations)
could be close to the conservation genetic borderline for avoiding inbreeding depression although we discuss some implications
of the analysis of temporal genetic change in populations with overlapping generations. 相似文献
16.
The transmembrane transport of anticancer drugs is mainly regulated by P-glycoprotein encoded by the human multidrug resistance
gene 1 gene (MDR1). Since there were controversies regarding the association between MDR1 C3435T polymorphism and response to chemotherapy among patients with advanced breast cancer, a meta-analysis of the link
was conducted. A total of 7 studies consist of 464 advanced breast cancer patients relating MDR1 C3435T polymorphism to the response of chemotherapy were included in this meta-analysis. The main analysis revealed a lack
of association between the MDR1 C3435T and response to chemotherapy, with odds ratios (ORs) and their corresponding 95% confidence intervals (CIs) of 1.37
(95% CI: 0.78–2.40), 1.17 (95% CI: 0.69–2.01), 1.18 (95% CI: 0.76–1.84) and 1.61 (95% CI: 0.70–3.68) for homozygous comparison,
heterozygous comparison, dominant model and recessive model, respectively. The subgroup analysis by ethnicity did not change
the pattern of results, with ORs of 0.99 (95% CI: 0.11–9.07), 0.68 (95% CI: 0.29–1.60), 0.81 (95% CI: 0.36–1.85) and 1.51
(95% CI: 0.77–2.96), in homozygous comparison, heterozygous comparison, dominant model and recessive model, respectively in
Caucasian, and 1.50 (95% CI: 0.75–3.03), 1.72 (95% CI: 0.85–3.47), 1.59 (95% CI: 0.90–2.80) and 2.29 (95% CI: 0.51–10.35),
respectively in Asian. The available evidence indicates that MDR1 C3435T polymorphism cannot be considered as a reliable predictor of response to chemotherapy in patients with advanced breast
cancer. 相似文献
17.
Assessing the genetic divergence of Pinus leucodermis Ant. endangered populations: use of molecular markers for conservation purposes 总被引:2,自引:0,他引:2
G. Bucci G. G. Vendramin L. Lelli F. Vicario 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1997,95(7):1138-1146
In this study, 23 previously identified Mendelian RAPD markers and 16 polymorphic allozymic markers were used to assess divergence
among two Greek populations and five Italian populations of Pinus leucodermis. Confidence intervals of observed genetic divergence were obtained using bootstrap analysis. Divergence among Italian populations
was found to be about as large as that between Italian and Greek populations. Since it is likely that the split of two nuclei
took place more than 10,000 years ago, a larger differentiation between, rather than within, the above nuclei was expected.
If genetic drift was responsible for the larger divergence of Italian populations, large randomly generated disequilibrium
between alleles at neutral, unlinked loci was expected. Indeed, the proportion of pairs of loci showing a non-random association
of alleles within each of the Italian populations was larger than what was expected by pure chance (7.95–10.88%). Effective
population size based on randomly generated disequilibrium was quite small for three out of the five populations considered
(N
e
=17.31±1.88, 16.57± 1.73, and 31.41±7.26, respectively). The implications of the results with respect to the conservation
of endangered species of trees are discussed.
Received: 27 April 1997 / Accepted: 14 June 1997 相似文献
18.
We established replicated experimental populations of the annual plant Clarkia pulchella to evaluate the existence of a causal relationship between loss of genetic variation and population survival probability. Two treatments differing in the relatedness of the founders, and thus in the genetic effective population size (Ne), were maintained as isolated populations in a natural environment. After three generations, the low Ne treatment had significantly lower germination and survival rates than did the high Ne treatment. These lower germination and survival rates led to decreased mean fitness in the low Ne populations: estimated mean fitness in the low Ne populations was only 21% of the estimated mean fitness in the high Ne populations. This inbreeding depression led to a reduction in population survival: at the conclusion of the experiment, 75% of the high Ne populations were still extant, whereas only 31% of the low Ne populations had survived. Decreased genetic effective population size, which leads to both inbreeding and the loss of alleles by genetic drift, increased the probability of population extinction over that expected from demographic and environmental stochasticity alone. This demonstrates that the genetic effective population size can strongly affect the probability of population persistence. 相似文献
19.
Milan Lstib?rek Kristyna Ivankov�� Jan Kadlec Jaroslav Kobliha Jaroslav Kl��p?t�� Yousry A. El-Kassaby 《Tree Genetics & Genomes》2011,7(5):1069-1078
We present a probabilistic model to minimize the fingerprinting effort associated with the implementation of the “breeding
without breeding” scheme under partial pedigree reconstruction. Our approach is directed at achieving a declared target population’s
minimum effective population size (N
e
), following the pedigree reconstruction and genotypic selection and is based on the graph theory algorithm. The primary advantage
of the proposed method is to reduce the cost associated with fingerprinting before the implementation of the pedigree reconstruction
for seed parent–offspring derived from breeding arboreta and production or natural populations. Stochastic simulation was
conducted to test the method’s efficiency assuming a simple polygenic model and a single trait. Hypothetical population consisted
of 30 parental trees that were paired at random (selfing excluded), resulting in 600 individuals (potential candidates for
forwards selection). The male parentage was assumed initially unknown. The model was used to estimate the minimum genotyping
sample size needed to reaching the prescribed N
e
. Results were compared with the known pedigree data. The model was successful in revealing the true relationship pattern
over the whole range of N
e
. Two to three offspring entered genotyping to meet the N
e
= 2 while 41 to 43 were required to satisfy the N
e
= 14. Importantly, genetic gain was affected at the lower limits of the genotyping effort. Doubling the number of parents
resulted in considerable reduction of the genotyping effort at higher N
e
values. 相似文献
20.
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