Assessing temporal changes in genetic diversity of maize varieties using microsatellite markers

To quantify genetic diversity among modern and earlier maize cultivars, 133 varieties, representative of the maize grown in France during the last five decades, were fingerprinted using 51 SSR. The varieties were grouped into four periods. For each period, allelic richness, genetic diversity and genetic differentiation among periods were computed. A total of 239 alleles were generated. Allelic richness, in terms of number of alleles per locus, for each period was 4.5, 3.6, 3.9 and 3.6 respectively. Genetic diversity corresponding to Neis unbiased heterozygosity was calculated, based on allelic frequencies. Values ranged from 0.56 to 0.61. Period I presented the highest genetic diversity, whereas the three other periods all presented a similar value. A great proportion of the total genetic diversity (H_T=0.59) was conserved within all periods (H_S=0.57), rather than among periods (G_ST=0.04). The analysis of molecular variance showed that the variation among periods represented only 10% of the total molecular variation. However, the differentiation among periods, although low, was significant, except for the last two periods. Our results showed that the genetic diversity has been reduced by about 10% in the maize cultivars bred before 1976 compared to those bred after 1985. The very low differentiation (G_ST=0.21%) observed among cultivars of the last two decades should alert French maize breeders to enlarge genetic basis in their variety breeding programmes.     

A new method for the partition of allelic diversity within and between subpopulations

A method is proposed for the analysis of allelic diversity in the context of subdivided populations. The definition of an allelic distance between subpopulations allows for the partition of total allelic diversity into within- and between-subpopulation components, in a way analogous to the classical partition of gene diversity. A new definition of allelic differentiation, A _ST , between subpopulations results from this partition, and is contrasted with the concept of allelic richness differentiation. The partition of allelic diversity makes it possible to establish the relative contribution of each subpopulation to within and between-subpopulation components of diversity with implications in priorisation for conservation. A comparison between this partition and that corresponding to allelic richness is illustrated with an example. Computer simulations are used to investigate the behaviour of the new statistic A _ST in comparison with F _ST for a finite island model under a range of mutation and migration rates. A _ST has less dependence on migration rate than F _ST for large values of migration rate, but the opposite occurs for low migration rates. In addition, the variance in the estimates of A _ST is higher than that of F _ST for low mutation rates, but the opposite for high mutation rates.     

Across-species patterns of genetic variation in forest trees of Central Europe

The study focuses on geographical patterns of genetic variation at allozyme loci common for four main tree species of Central Europe (Norway spruce, silver fir, common beech and sessile oak). Moving-window averaging of four indicators of allelic richness and diversity (proportion of polymorphic loci, mean number of alleles per locus, effective number of alleles and expected heterozygosity) with window size of 50 × 50 km was used to identify the patterns. Moreover, local genetic divergence was assessed using the G _ST (Nei, Molecular population genetic and evolution, Amsterdam and Oxford, North-Holland, 1975) and D _j (Gregorius and Roberds, Theor Appl Genet 71:826–834, 1986) statistics for common beech and silver fir, where raw genotype data were available. Spatial patterns of diversity and allelic richness were quite similar. Romanian Carpathians were identified as the most important hotspot of genetic diversity and evolutionary divergence in Central Europe. Implications for genetic conservation are briefly discussed.     

High level of genetic differentiation for allelic richness among populations of the argan tree [Argania spinosa (L.) Skeels] endemic to Morocco

Genetic diversity at nine isozyme loci was surveyed in an endangered tree species, the argan tree, endemic to south-western Morocco. The species is highly diverse (3.6 alleles/locus) with populations strongly differentiated from each other (F _ST=0.25). This example is used to illustrate a method for standardizing measures of allelic richness in samples of unequal sample sizes, which was developed for the estimation of the number of species and relies on the technique of rarefaction. In addition, it is shown that the measure of subdivision, _ST, obtained when allelic richness is used in place ofh (Nei's index of diversity), is much larger than the F _ST [e.g. _ST(40)=0.52, where (40) indicates the specified sample used to estimate the allelic richness]. This suggests that rare alleles (which strongly influence measures of allelic richness) have a more scattered distribution than more frequent ones, a result which raises special conservation issues for the argan tree.     

Genetic variability and the effect of habitat fragmentation in spotted suslik Spermophilus suslicus populations from two different regions

Endangered species worldwide exist in remnant populations, often within fragmented landscapes. Although assessment of genetic diversity in fragmented habitats is very important for conservation purposes, it is usually impossible to evaluate the amount of diversity that has actually been lost. Here, we compared population structure and levels of genetic diversity within populations of spotted suslik Spermophilus suslicus, inhabiting two different parts of the species range characterized by different levels of habitat connectivity. We used microsatellites to analyze 10 critically endangered populations located at the western part of the range, where suslik habitat have been severely devastated due to agriculture industrialization. Their genetic composition was compared with four populations from the eastern part of the range where the species still occupies habitat with reasonable levels of connectivity. In the western region, we detected extreme population structure (F _ST = 0.20) and levels of genetic diversity (Allelic richness ranged from 1.45 to 3.07) characteristic for highly endangered populations. Alternatively, in the eastern region we found significantly higher allelic richness (from 5.09 to 5.81) and insignificant population structure (F _ST = 0.03). As we identified a strong correlation between genetic and geographic distance and a lack of private alleles in the western region, we conclude that extreme population structure and lower genetic diversity is due to recent habitat loss. Results from this study provide guidelines for conservation and management of this highly endangered species.     

Genetic Structure of Wild Rice Oryza Glumaepatula Populations in Three Brazilian Biomes Using Microsatellite Markers

The existence of Oryza glumaepatula is threatened by devastation and, thus, the implementation of conservation strategies is extremely relevant. This study aimed to characterize the genetic variability and estimate population parameters of 30 O. glumaepatula populations from three Brazilian biomes using 10 microsatellite markers. The levels of allelic variability for the SSR loci presented a mean of 10.3 alleles per locus and a value of 0.10 for the average allelic frequency value. The expected total heterozygosity (H_e) ranged from 0.63 to 0.86. For the 30 populations tested, the mean observed (H_o) and expected heterozygosities (H_e) were 0.03 and 0.11within population, respectively, indicating an excess of homozygotes resulting from the preferentially self-pollinating reproduction habit. The estimated fixation index ( _IS ) was 0.79 that differed significantly from zero, indicating high inbreeding within each O. glumaepatula population. The total inbreeding of the species (_IT ) was 0.98 and the genetic diversity indexes among populations, _ST and _ST, were 0.85 and 0.90, respectively, indicating high genetic variability among them. Thus, especially for populations located in regions threatened with devastation, it is urgent that in situ preservation conditions should be created or that collections be made for ex situ preservation to prevent loss of the species genetic variability.     

REDUCED GENETIC DIVERSITY AND INCREASED POPULATION DIFFERENTIATION IN PERIPHERAL AND OVERHARVESTED POPULATIONS OF GIGARTINA SKOTTSBERGII (RHODOPHYTA,GIGARTINALES) IN SOUTHERN CHILE1

This study assesses two hypotheses on the genetic diversity of populations of Gigartina skottsbergii Setchell et Gardner (Rhodophyta, Gigartinales) at the border of the species distribution: 1) peripheral populations display a reduced genetic diversity compared with central populations, and 2) genetic differentiation is higher among peripheral than among central populations. Two peripheral and four central populations were sampled along the Chilean coast and 113 haploid individuals were analyzed using 17 random amplification of polymorphic DNA loci. The genetic diversity was estimated by allele diversity (H_e), allele richness (Â), and the mean pair‐wise differences among multilocus genotypes. All three estimates consistently and significantly indicated a lower genetic diversity within the peripheral than within the central populations. Genetic differentiation between the two peripheral populations was stronger (F_ST=0.35) than between central populations at similar spatial scales (F_ST ranging from 0 to 0.25). In addition, it appeared from the distribution of pair‐wise differences that peripheral populations are in demographic expansion after a recent bottleneck. The results are discussed in the specific context of potential overharvesting of these wild populations.     

Population genetic inferences using immune gene SNPs mirror patterns inferred by microsatellites

Single nucleotide polymorphisms (SNPs) are replacing microsatellites for population genetic analyses, but it is not apparent how many SNPs are needed or how well SNPs correlate with microsatellites. We used data from the gopher tortoise, Gopherus polyphemus—a species with small populations, to compare SNPs and microsatellites to estimate population genetic parameters. Specifically, we compared one SNP data set (16 tortoises from four populations sequenced at 17 901 SNPs) to two microsatellite data sets, a full data set of 101 tortoises and a partial data set of 16 tortoises previously genotyped at 10 microsatellites. For the full microsatellite data set, observed heterozygosity, expected heterozygosity and F_ST were correlated between SNPs and microsatellites; however, allelic richness was not. The same was true for the partial microsatellite data set, except that allelic richness, but not observed heterozygosity, was correlated. The number of clusters estimated by structure differed for each data set (SNPs = 2; partial microsatellite = 3; full microsatellite = 4). Principle component analyses (PCA) showed four clusters for all data sets. More than 800 SNPs were needed to correlate with allelic richness, observed heterozygosity and expected heterozygosity, but only 100 were needed for F_ST. The number of SNPs typically obtained from next‐generation sequencing (NGS) far exceeds the number needed to correlate with microsatellite parameter estimates. Our study illustrates that diversity, F_ST and PCA results from microsatellites can mirror those obtained with SNPs. These results may be generally applicable to small populations, a defining feature of endangered and threatened species, because theory predicts that genetic drift will tend to outweigh selection in small populations.     

Loss of historical immigration and the unsuccessful rehabilitation of extirpated salmon populations

Comprehensive evaluations of multiple genetic factors are rarely undertaken in rehabilitation attempts of extirpated populations, despite a growing need to address why some rehabilitation projects succeed and others fail. Using temporally-spaced samples of microsatellite DNA, we tested several genetic hypotheses that might explain an unsuccessful attempt to re-establish Atlantic salmon populations (Salmo salar) in two rivers of the inner Bay of Fundy, Canada. Census sizes (N) in both populations plummeted to near zero from initial increases after reintroduction/human-mediated recolonization occurred. Over the same period (1974–1996), both populations were characterized by low or relatively low effective sizes (N _e ) and temporally unstable genetic structuring, whereas neighbouring populations, known historically for their significant salmon production, were not. Despite evidence for genetic bottlenecking and continual linkage disequilibrium over time in both populations, neither exhibited detectable inbreeding or a significant loss of allelic diversity or heterozygosity relative to known donor/source populations. Ratios of N _e to N also increased with decreasing N in both populations, implying a buffering capacity against losses of genetic diversity at depressed abundances. Most significantly, multiple lines of evidence were consistent with the hypothesis that there has been substantial and recurrent asymmetric migration (migration rate, m) from neighbouring areas into both populations even after initial rehabilitation. This included migration from a historically productive population that became extirpated during the course of rehabilitation efforts, indicating that both populations might have naturally depended on immigration from neighbouring areas for persistence. Our results highlight the value of incorporating temporal genetic data beyond commonly used metrics of neutral genetic diversity (F _ST, allelic richness, heterozygosity) to evaluate rehabilitation successes or failures. They also illustrate how the joint evaluation of multiple genetic concerns in rehabilitation attempts, at spatial scales beyond donor and rehabilitated populations, is useful for focusing future rehabilitation efforts.     

Human disturbance reduces genetic diversity of an endangered tropical tree, <Emphasis Type="Italic">Prunus africana</Emphasis> (Rosaceae)

Human activities such as fragmentation and selective logging of forests can threaten population viability by modification of ecological and genetic processes. Using six microsatellite markers, we examined the effects of forest fragmentation and local disturbance on the genetic diversity and structure of adult trees (N = 110) and seedlings (N = 110) of Prunus africana in Kakamega Forest, western Kenya. Taking samples of adults and seedlings allowed for study of changes in genetic diversity and structure between generations. Thereby, adults reflect the pattern before and seedlings after intensive human impact. Overall, we found 105 different alleles in the six loci examined, 97 in adults and 88 in seedlings. Allelic richness and heterozygosity were significantly lower in seedlings than in adults. Inbreeding increased from adult tree to seedling populations. Genetic differentiation of adult trees was low (overall F _ST = 0.032), reflecting large population sizes and extensive gene flow in the past. Genetic differentiation of seedlings was slightly higher (overall F _ST = 0.044) with all of the 28 pairwise F _ST-values being significantly different from zero. These results suggest that human disturbance in Kakamega Forest has significantly reduced allelic richness and heterozygosity, increased inbreeding and slightly reduced gene flow in P. africana in the past 80–100 years.     

Genetic Variation in Fragmented Forest Stands of the Andean Oak Quercus humboldtii Bonpl. (Fagaceae)1

Quercus humboldtii is a montane forest dominant species in Colombia, which has experienced significant habitat loss. Using three microsatellite loci, we compared the genetic diversity of adults and seedlings in fragments of small and large size. Results show high genetic diversity, comparable to other temperate oak species (H_o= 0.813, H_e= 0.780, and f=?0.044). However, allelic richness reduction in seedlings of the most fragmented part of the landscape, suggested restricted gene flow and risk of future genetic bottlenecks, if larger tracts of forest disappear.     

Genetic variation in island populations of tuatara (<Emphasis Type="Italic">Sphenodon</Emphasis> spp) inferred from microsatellite markers

Tuatara (Sphenodon spp) populations are restricted to 35 offshore islands in the Hauraki Gulf, Bay of Plenty and Cook Strait of New Zealand. Low levels of genetic variation have previously been revealed by allozyme and mtDNA analyses. In this new study, we show that six polymorphic microsatellite loci display high levels of genetic variation in 14 populations across the geographic range of tuatara. These populations are characterised by disjunct allele frequency spectra with high numbers of private alleles. High F _ST (0.26) values indicate marked population structure and assignment tests allocate 96% of all individuals to their source populations. These genetic data confirm that islands support genetically distinct populations. Principal component analysis and allelic sequence data supplied information about genetic relationships between populations. Low numbers of rare alleles and low allelic richness identified populations with reduced genetic diversity. Little Barrier Island has very low numbers of old tuatara which have retained some relictual diversity. North Brother Island’s tuatara population is inbred with fixed alleles at 5 of the 6 loci.     

Spatial and Temporal Genetic Variation of Green Mussel, Perna viridis in the Gulf of Thailand and Implication for Aquaculture

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, CI_0.95 = 0.0020–0.0083 for the samples collected in January, 2007, and F _ST = 0.0088, CI_0.95 = 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.     

Genetic diversity and structure of the endemic Caesalpinia hintonii complex (Leguminosae: Caesalpinioideae) in Mexico

The Caesalpinia hintonii complex is formed by five endemic species (C. hintonii, C. laxa, C. macvaughii, C. melanadenia and C. epifanioi) occurring in central Mexico. This species complex is under incipient genetic divergence as by-product of local adaptations in reproductive and morphological traits to different habitats. We estimate the genetic variation and structure of populations of this species complex to assess the extent of genetic differentiation among populations and related species along its geographic distribution. Estimations of genetic diversity and structure were done based on ten enzymes and 18 loci. Mean number of alleles per locus ranged from 1.5 to 1.9. Polymorphic loci ranged from 42.1 to 68.4. Observed (H_o: range 0.191–0.275) and expected (H_e: range 0.205–0.317) heterozygosities in this complex were higher compared with other endemic and legume species. Neis genetic diversity estimates showed that most genetic variation was found within (H_S = 0.325) rather than among populations (D_ST = 0.085). Populations of the species C. hintonii showed a considerable genetic differentiation (F_ST = 0.207). The results of genetic diversity and structure within and among populations are in accord with the great morphological differentiation described for this species complex.     

A mountain range is a strong genetic barrier between populations of <Emphasis Type="Italic">Afzelia quanzensis</Emphasis> (pod mahogany) with low genetic diversity

Understanding patterns of genetic diversity of plants is important in guiding conservation programs. The aim of our study was to characterize genetic diversity in Afzelia quanzensis, an economically important African tree species. We genotyped 192 individuals at 10 nuclear microsatellite loci. Samples were collected from nine sites in Zimbabwe, five in the north and four in the south, separated by a mountain range, the Kalahari-Zimbabwe axis. Overall, genetic diversity was relatively low across all sites (expected heterozygosity (H _E)?=?0.452, mean number of alleles (A)?=?4.367, allelic richness (A _R)?=?2.917, effective number of alleles (A _E)?=?2.208, and private allelic richness (PA_R)?=?0.197). Genetic diversity estimates, H _E, A, A _R, and PA_R, were not significantly different between northern and southern sites. Allelic richness was significantly higher in southern sites. Significant population differentiation was observed among all sites (F _ST ?=?0.0936, G′ _ST ?=?0.1982, G _ST ?=?0.1001, D _JOST?=?0.0598). STRUCTURE analysis and principal components analysis identified two gene pools, one predominantly made up of southern individuals, and the other of northern individuals. A Monmonier’s function detected a genetic barrier that coincided with the Kalahari-Zimbabwe axis. The relatively low level of genetic diversity in A. quanzensis may reduce adaptability and limit future evolutionary responses. All sites should be monitored for deleterious effects of low genetic diversity, and genetic resource management should take into consideration the existence of the distinct gene pools to capture the entire extant genetic variation.     

Negligible impact of deer-induced habitat degradation on the genetic diversity of extant <Emphasis Type="Italic">Bombus diversus</Emphasis> populations in comparison with museum specimens

The genetic diversity of bumblebees can be adversely affected by habitat degradation. An overabundance of deer has altered the composition and diversity of herbaceous plants in many places of the world, resulting in decreases of herbaceous flowers. Populations of Bombus diversus may be strongly affected by this degradation of habitat in the Ashiu primary beech forest in Kyoto, Japan. To estimate the effects of deer browsing on B. diversus populations, we analyzed and compared the genetic diversity of the extant population in Ashiu to museum specimens collected prior to heavy deer browsing in Ashiu (1980s) and the extant population in Hyonosen primary beech forest in Tottori, Japan, which has not been as severely degraded by deer. We successfully amplified DNA from ~20-year-old museum specimens and determined the genetic diversity of B. diversus in Ashiu populations from the 1980s. Results were analyzed for indications of a bottleneck as well as estimates of N _e, allelic richness, rare allelic richness, expected heterozygosity, and the effective number of alleles. Our findings did not reveal clear evidence of degradation in genetic diversity of the extant Ashiu population compared to the museum specimens or to the Hyonosen population. Thus, the Ashiu population of B. diversus appears to have maintained a level of genetic diversity during 20 years irrespective of habitat degradation and the levels have been similar to that of the Hyonosen population.     

Genetic diversity and population structure of the endangered insect species Carabus variolosus in its western distribution range: Implications for conservation

Genetic variation was assessed in the endangered species C. variolosus (Coleoptera: Carabidae), which is listed in the European Habitats and Species Directive. Twelve populations from the north-western margin of its range in Germany and France to the border region between Slovenia and Croatia were investigated for variation at 16 allozyme loci. In general, genetic diversity was rather low as indicated by a mean allelic richness of 1.3 alleles per locus, a mean gene diversity (H _E ) of 0.071 and a mean proportion of polymorphic loci (P _95% ) of 16%. Genetic diversity did not change directionally from the margin towards the core of the range. Very high differentiation between populations (overall F _ST  = 0.465), the results of a Mantel test, and poor accordance between geographical and genetic distance suggest a high degree of isolation of the island-like distributed populations. High F _ST values and genetic distance measures, even between geographically close populations within the same drainage, confirm a very low dispersal power of this habitat specialist of headwater areas and swamps in woodlands, even in comparison with other flightless beetles. It is concluded that the majority of populations are demographically independent. Hierarchical F-statistics indicate that almost half of the genetic variance is found between regions and populations. Therefore, we recommend that conservation efforts consider every population as a management unit and aim to maintain as many populations as possible over as many regions as possible.     

Contrasted levels of genetic diversity in a benthic Mediterranean octocoral: Consequences of different demographic histories?

Understanding the factors explaining the observed patterns of genetic diversity is an important question in evolutionary biology. We provide the first data on the genetic structure of a Mediterranean octocoral, the yellow gorgonian Eunicella cavolini, along with insights into the demographic history of this species. We sampled populations in four areas of the Mediterranean Sea: continental France, Algeria, Turkey, and the Balearic and Corsica islands. Along French coasts, three sites were sampled at two depths (20 and 40 m). We demonstrated a high genetic structure in this species (overall F_ST = 0.13), and most pairwise differentiation tests were significant. We did not detect any difference between depths at the same site. Clustering analyses revealed four differentiated groups corresponding to the main geographical areas. The levels of allelic richness and heterozygosity were significantly different between regions, with highest diversity in Algeria and lowest levels in Turkey. The highest levels of private allelic richness were observed in Algeria followed by Turkey. Such contrasted patterns of genetic diversity were not observed in other Mediterranean octocorals and could be the result of different evolutionary histories. We also provide new empirical evidence of contrasting results between tests and model‐based studies of demographic history. Our results have important consequences for the management of this species.     

Conservation genomics of an Australian cycad Cycas calcicola,and the Absence of Key Genotypes in Botanic Gardens

Understanding the genetic diversity of wild populations is fundamental to conserving species in-situ and ex-situ. To aid conservation plans and to inform ex-situ conservation, we examined the genetic diversity of the cycad Cycas calcicola (Cycadaceae). Samples were collected from wild populations in the Litchfield National Park and Katherine regions in the Northern Territory, Australia. Additional samples were obtained from botanic garden plants that were originally collected in the Katherine region, Daly River and Spirit Hills in the Northern Territory, Australia. Using RADseq we recovered 2271 informative genome-wide SNPs, revealing low to moderate levels of gene diversity (uH_e?=?0.037 to 0.135), very low levels of gene flow, and significant levels of inbreeding (mean F_IS?=?0.491). Population structure and multivariate analysis showed that populations fall into two genetic groups (Katherine vs Litchfield?+?Daly River?+?Spirit Hills). Genetic differentiation was twice as high between populations of the Katherine and Litchfield regions (F_ST?~?0.1) compared to within these two regions (F_ST?~?0.05). Increasing population fragmentation together with high levels of inbreeding and very little gene flow are concerning for the future adaptability of this species. The results indicated that the ex-situ collections (1) had significantly lower genetic diversity than the wild populations, and (2) only partly capture the genetic diversity present, particularly because the Litchfield National Park populations are not represented. We recommend that ex-situ collections be expanded to incorporate the genetic diversity found in Litchfield National Park and to increase the number of representatives from Daly River/Spirit Hills, and that in-situ populations from the Katherine and Greater Litchfield regions be conserved as separate management units.

     

Population genetics after fragmentation: the case of the endangered Spanish imperial eagle (Aquila adalberti)

The highly endangered Spanish imperial eagle, Aquila adalberti, has suffered from both population decline and fragmentation during the last century. Here we describe the current genetic status of the population using an extensive sampling of its current distribution range and both mitochondrial control region sequences and nuclear microsatellite markers. Results were evaluated in comparison to those obtained for the Eastern imperial eagle, Aquila heliaca, its nearest extant relative. Mitochondrial haplotype diversity was lower in the Spanish than in the Eastern species whereas microsatellite allelic richness and expected heterozygosity did not differ. Both allelic richness and expected heterozygosity were lower in the small Parque Nacional de Doñana breeding nucleus compared to the remaining nuclei. A signal for a recent genetic bottleneck was not detected in the current Spanish imperial eagle population. We obtained low but significant pairwise F_ST values that were congruent with a model of isolation by distance. F_ST and exact tests showed differentiation among the peripheral and small Parque Nacional de Doñana population and the remaining breeding subgroups. The centrally located Montes de Toledo population did not differ from the surrounding Centro, Extremadura and Sierra Morena populations whereas the latter were significantly differentiated. On the other hand, a Bayesian approach identified two groups, Parque Nacional de Doñana and the rest of breeding nuclei. Recent migration rates into and from Parque Nacional de Doñana and the rest of breeding nuclei were detected by assignment methods and estimated as 2.4 and 5.7 individuals per generation, respectively, by a Bayesian approach. We discuss how management strategies should aim at the maintenance of current genetic variability levels and the avoidance of inbreeding depression through the connection of the different nuclei.