Spatial heterogeneity of mitochondrial DNA and allozymes among populations of white-tailed deer and mule deer.

A white-tailed deer (Odocoileus virginianus) population in northeastern Minnesota and a mule deer (O. hemionus) population in the Bridger Mountains Montana, have previously been shown to be spatially subdivided into contiguous subpopulations. We assessed the degree of genetic differentiation among subpopulations and tested the hypothesis that differentiation will be greater for mitochondrial DNA (mtDNA) than for nuclear-encoded allozymes. Differentiation of the white-tailed deer subpopulations was significant for two allozyme loci but not for mtDNA, and the overall degree of differentiation was low. Gene flow, recent founding of the subpopulations, and polygamous breeding structure may all have contributed to this pattern. Greater differentiation was evident among disjunct populations than between the contiguous subpopulations of white-tailed deer. The contiguous mule deer subpopulations were significantly differentiated for mtDNA and one allozyme locus. Differentiation was greater for mtDNA than for allozymes. These results are consistent with demographic data that indicate mule deer males disperse more than do females. Disjunct mule deer populations may be similar or dramatically different in mtDNA haplotype frequencies that do not necessarily vary with geographic distance. Current and historical gene flow and breeding structure will influence population genetic patterns.     

Rapid evolutionary responses in a translocated population of intertidal snail (<Emphasis Type="Italic">Bembicium vittatum</Emphasis>) utilise variation from different source populations

The artificial movement of individuals between populations (translocation) can be an effective way to increase genetic diversity within populations, but few studies have undertaken long term genetic monitoring to determine if variation introduced by translocation is maintained over many generations or whether it can be used to adapt to local conditions. Here, we report on the changes in morphological and molecular variation over a 12-year period in a population of an intertidal littorine snail (Bembicium vittatum) that was created by mixing individuals from three geographically disjunct populations. These source populations differ genetically in shell shape and in allele frequency at several allozyme loci. We found that the translocated population had higher allozyme diversity than any of the source populations and that this pattern was maintained over multiple generations. Variation in shell shape also increased, but this declined over time as shells became taller. Some allozyme loci also showed significant changes in frequency over time. These changes were not consistently towards the genetic makeup of a single source population, and in the case of shell shape, were towards a phenotype that was most suited to the local environment. Our results suggest that genetic variation introduced into a population by translocation can be rapidly incorporated and used to adapt to local conditions without domination by a single source population’s genome. However, more studies are needed before generalisations on the benefits of mixing individuals from disjunct populations can be made.     

Isolation of new microsatellite loci from the Green Lizard (Lacerta viridis viridis)

Twelve new microsatellite loci were isolated from the Green Lizard (Lacerta viridis viridis). Primers for 28 loci were designed and 18 of these loci amplified well for 10 individuals of four populations. Twelve of these loci were further characterized for a population in Hungary. The results document the suitability of these identified loci for the characterization of the genetic diversity of the endangered species L. viridis viridis.     

Population genetic consequences of geographic disjunction: a prairie plant isolated on Great Lakes alvars

Species may often exhibit geographic variation in population genetic structure due to contemporary and historical variation in population size and gene flow. Here, we test the predictions that populations on the margins of a species' distribution contain less genetic variation and are more differentiated than populations towards the core of the range by comparing patterns of genetic variation at five microsatellite loci between disjunct and core populations of the perennial, allohexaploid herb Geum triflorum. We sampled nine populations isolated on alvar habitat within the eastern Great Lakes region in North America, habitats that include disjunct populations of several plant species, and compared these to 16 populations sampled from prairie habitat throughout the core of the species' distribution in midwestern Canada and the USA. Alvar populations exhibited much lower within-population diversity and contained only a subset of alleles found in prairie populations. We detected isolation by distance across the species' range and within alvar and prairie regions separately. As predicted, genetic differentiation was higher among alvar populations than among prairie populations, even after controlling for the geographic distance between sampled populations. Low diversity and high differentiation can be accounted for by the greater contemporary spatial isolation of alvar populations. However, the genetic structure of alvar populations may also have been influenced by postglacial range expansion and contraction. Our results are consistent with alvar populations being founded during an expansion of prairie habitat during the warmer, hypsithermal period approximately 5000 bp and subsequently becoming stranded on isolated alvar habitat as the climate grew cooler and wetter.     

Conservation genetics of Amorpha georgiana (Fabaceae), an endangered legume of the Southeastern United States

Amorpha georgiana (Fabaceae) is an endangered legume species found in longleaf pine savannas in the Southeastern United States. Approximately 900 individuals and 14 populations remain, most of which are concentrated in North Carolina. Eleven microsatellite loci were used to explore genetic diversity, population structure and recent population bottlenecks using genotypic data from 132 individuals collected at ten different localities. Although A. georgiana is quite rare, it exhibited high levels of genetic diversity (17.7 alleles/locus; H _o = 0.65, H _E = 0.75). Most of the genetic variation was found within rather than between populations of this species. The single remaining Georgia population was well differentiated from populations of the Carolinas ( F _ST > 0.1), which had weaker structure among them ( F _ST < 0.1). Only a geographically disjunct population showed strong evidence of a recent population bottleneck, perhaps due to a recent founder event. Hybridization with A. herbacea was also detected. For conservation management plans, A. georgiana populations in each geographic region (North Carolina, South Carolina and Georgia) plus a disjunct population in North Carolina (Holly Shelter) should be treated as separate management units for which in situ conservation, including habitat restoration and use of prescribed burns, should ensure persistence of this species and preservation of its evolutionary potential.     

Genetic similarity of disjunct populations of the giant sea bass Stereolepis gigas

Sequence variation in nuclear and mitochondrial genes of the giant sea bass Stereolepis gigas collected from the Pacific coast and the northern Sea of Cortez was examined. Restriction fragment length polymorphism analysis and direct sequencing showed extremely low mtDNA sequence diversity (13 closely related haplotypes with no evidence of geographical population subdivision). The mitochondrial haplotype mismatch distribution is consistent with a population expansion following the Last Pleistocene glaciation. Differences in single nucleotide polymorphism frequencies between Pacific and Sea of Cortez populations were detected at two of four nuclear loci, which may reflect natural selection or genetic drift in populations with low effective numbers of males. Although Pacific coast and Sea of Cortez populations of giant sea bass do not exhibit the mitochondrial phylogenetic break characteristic of many species with disjunct Pacific and Gulf populations, the possibility of genetic differentiation at nuclear loci suggests that a cautious approach to broodstock selection for captive breeding and restoration programmes be exercised.     

Genetic diversity and population parameters of sea otters, Enhydra lutris, before fur trade extirpation from 1741-1911

All existing sea otter, Enhydra lutris, populations have suffered at least one historic population bottleneck stemming from the fur trade extirpations of the eighteenth and nineteenth centuries. We examined genetic variation, gene flow, and population structure at five microsatellite loci in samples from five pre-fur trade populations throughout the sea otter's historical range: California, Oregon, Washington, Alaska, and Russia. We then compared those values to genetic diversity and population structure found within five modern sea otter populations throughout their current range: California, Prince William Sound, Amchitka Island, Southeast Alaska and Washington. We found twice the genetic diversity in the pre-fur trade populations when compared to modern sea otters, a level of diversity that was similar to levels that are found in other mammal populations that have not experienced population bottlenecks. Even with the significant loss in genetic diversity modern sea otters have retained historical structure. There was greater gene flow before extirpation than that found among modern sea otter populations but the difference was not statistically significant. The most dramatic effect of pre fur trade population extirpation was the loss of genetic diversity. For long term conservation of these populations increasing gene flow and the maintenance of remnant genetic diversity should be encouraged.     

Low population genetic differentiation in the Orchidaceae: implications for the diversification of the family

A leading hypothesis for the immense diversity of the Orchidaceae is that skewed mating success and small, disjunct populations lead to strong genetic drift and switches between adaptive peaks. This mechanism is only possible under conditions of low gene flow that lead to high genetic differentiation among populations. We tested whether orchids typically exhibit high levels of population genetic differentiation by conducting a meta‐analysis to compare mean levels of population genetic differentiation (F_ST) between orchids and other diverse families and between rare and common orchids. Compared with other families, the Orchidaceae is typically characterized by relatively low genetic differentiation among populations (mean F_ST = 0.146) at allozyme loci. Rare terrestrial orchids showed higher population genetic differentiation than common orchids, although this value was still lower than the mean for most plant families. All lines of evidence suggest that orchids are typically characterized by low levels of population genetic differentiation, even in species with naturally disjunct populations. As such, we found no strong evidence that genetic drift in isolated populations has played a major role in the diversification of the Orchidaceae. Further research into the diversification of the family needs to unravel the relative roles of biotic and environmental selective pressures in the speciation of orchids.     

Comparison of population genetic diversity between a rare, narrowly distributed species and a common, widespread species of Alnus (Betulaceae)

Comparisons of population genetic diversity between related rare and widespread species provide valuable insights to the consequences of rarity and are critical for conservation planning. Population genetic diversity of A. maritima, a rare species, was compared with its common, widespread congener A. serrulata to evaluate the impacts of small population size and high isolation on genetic diversity in A. maritima and to provide population genetic data to be used in conservation planning for A. maritima. Genetic data were also used to evaluate whether the disjunct distribution of A. maritima was due to range reduction or anthropogenic dispersal. Genetic diversity was lower in A. maritima (H(e) = 0.217) than in A. serrulata (H(e) = 0.268), and there is also higher inbreeding within A. maritima populations (f = 0.483) than A. serrulata populations (f = 0.269). The partitioning of genetic variation was also higher among A. maritima populations (Θ = 0.278), but not significantly different from that of A. serrulata (Θ = 0.197). Significant genetic differences among A. maritima populations support using local populations as seed sources for regional conservation efforts. The results also indicate that the highly disjunct distribution of A. maritima is due to natural range reduction in the past and not anthropogenic establishment of Oklahoma and Georgia populations.     

Lack of congruence between morphometric evolution and genetic differentiation suggests a recent dispersal and local habitat adaptation of the Madeiran lizard Lacerta dugesii

Genetic differentiation among nine populations of the endemic lizard Lacerta dugesii Milne-Edwards 1829 (Lacertidae) from four groups of islands constituting the Archipelago of Madeira, was investigated by protein electrophoresis at 23 enzyme loci. Among twenty polymorphic loci, the total genetic diversity was due primarily to intra-population variation. The allele and genotypic frequencies among populations showed some heterogeneity, allowing the species to present a structuring pattern compatible with their geographical clustering. Some evidence suggests that selection acting on some loci in different ecological conditions may be responsible for the clustering of the populations studied. There was no apparent isolation effect expected under an "island" model of population divergence, and no correlation was found between genetic and geographic distances among populations. Morphological variation of the proposed three L. dugesii subspecies is not congruent with the allozyme analysis. This most probably suggests a rapid colonization of the islands followed by a strong effect of selection operating over the morphological characters used to define the subspecies.     

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.     

Conservation genetics of the Common Tern (Sterna hirundo) in the North Atlantic region; implications for the critically endangered population at Bermuda

Common Terns nesting at Bermuda are isolated by 1,000–4,000?km from other populations of the species around the North Atlantic Ocean. This population experienced a severe demographic bottleneck as a result of a hurricane in 2003 and was subsequently re-established by four males and four females. Using seven microsatellite loci, we compared the genetic diversity of the pre- and post-bottleneck populations, compared the genetic profile of the Bermuda population with those of other populations around the North Atlantic Ocean and mainland Europe, and assessed the potential contribution of immigration to genetic diversity. We found a loss of genetic diversity (number of alleles and heterozygosity) in the post-bottleneck Bermudian population (4.6–2.9 and 0.56–0.52, respectively). We also report significant differentiation among all sampled locations (global F_ST?=?0.16) with no evidence for immigration into Bermuda. Common Terns from the Azores were genetically more similar to those from mainland North America than to those from Bermuda or mainland Europe. Our results suggest that the critically endangered population in Bermuda is genetically distinct and requires continued and enhanced conservation priority.     

Impact of founder population, drift and selection on the genetic diversity of a recently translocated tree population

Recently established, temperate tree populations combine a high level of differentiation for adaptive traits, suggesting rapid genetic evolution, with a high level of genetic diversity within population, suggesting a limited impact of genetic drift and purifying selection. To study experimentally the evolutionary forces in a recently established population, we assessed the spatial and temporal patterns of genetic diversity within a disjunct population of Cedrus atlantica established 140 years ago in south-eastern France from a North African source. The population is expanding through natural regeneration. Three generations were sampled, including founder trees. We analysed 12 isozyme loci, three of which were previously found in tight association with selected genes, and quantitative traits. No bottleneck effect was detected in the founder generation, but a simple test of allelic association revealed an initial disequilibrium which disappeared in the following generations. The impact of genetic drift during secondary evolution was limited, as suggested by the weak temporal differentiation. The genetic load was not reduced after 3 generations, and the quantitative variation for adaptive traits did not change either. Thus, initial genetic changes first proceed from a rapid re-organisation of the diversity through mating and recombination, whereas genetic erosion through drift and selection is delayed due to temporal and spatial stochasticity. Two life-history traits of trees contribute to slowing down the processes of genetic erosion: perenniality and large spatial scale. Thus, one would expect recently established tree populations to have a higher diversity than older ones, which seems in accordance with experimental surveys.     

The structure of allozyme and leaf shape variation in isolated, range-margin populations of the shrub Hippocrepis emerus (Leguminosae)

We investigated allozyme variation and phenotypic variation in leaf shape in 15 populations of the shrub Hippocrepis emerus (Leguminosae) from the three isolated, regional populations in Scandinavia and analysed patterns of differentiation and the hierarchical structuring of diversity on different geographic scales There are pronounced geographic differences between the Norwegian and Swedish isolates of the species and most of the polymorphic allozyme loci show reciprocal fixation in the two isolates The Scandinavian populations of H emerus are not only disjunct on a macrogeographic scale but also show considerable disjunction within regions Within the Oland regional population, a central group of populations shows low levels of Inter-population differentiation the Gotland group of populations is related to this core group of Oland populations The geographically marginal populations on Oland are spatially isolated and show a higher degree of divergence between populations than does the central group of Oland populations We interpret genetic divergence between the marginal populations in terms of genetic drift - as a result of historical fluctuations in habitat availability and population size     

Genic Heterozygosity and Protein Polymorphism among Local Populations of OENOTHERA BIENNIS

Twenty enzyme loci were studied in 44 Illinois populations of Oenothera biennis; four were polymorphic. Most of the variation was distributed between populations. Fifty-nine percent of the populations had one genotype, 27% two genotypes and the remaining 16% from three to five genotypes; the average was 1.50. The proportion of genetic diversity present in single populations is.38 of that present in the state. Members of single populations were uniformly heterozygous for 1 to 4 loci. The mean heterozygosity per population ranged from 0 to 20%. For Illinois populations collectively, heterozygosity averaged 4.5%. There was much gene frequency heterogeneity between populations. The true standardized genetic variance among populations for alleles at polymorphic loci varied from.40 to.78. Populations from Cook County were much more similar inter se than those downstate, had fewer genotypes and polymorphic loci, and had less heterozygosity than downstate populations. The mean normalized genetic identity among Cook County populations was.987 versus.947 for downstate populations. The mean number of genotypes per population in Cook County was 1.06 versus 2.40 in downstate populations. There was only one polymorphic locus in Cook County, VLP. The genetic structure of Oe. biennis suggests that single populations are colonized by one, or at best a few individuals. Cook County populations are judged to be less variable than downstate populations because the mean age of the populations probably is less than that of those downstate.     

ALLOZYME VARIATION,GENECOLOGY, AND PHYTOGEOGRAPHY OF ANTENNARIA ARCUATA (ASTERACEAE), A RARE SPECIES FROM THE GREAT BASIN AND RED DESERT WITH SMALL DISJUNCT POPULATIONS

Antennaria arcuata (Asteraceae: Inuleae) is a rare sexual diploid species that occurs in three disjunct regions of Idaho, Nevada, and Wyoming. Isozyme diversity in six populations of the species from the three regions utilized 26 putative loci to provide clues to its population genetic structure. Results show that, in general, the amount of genetic diversity in A. arcuata is very low in comparison to other sexual species of Antennaria. The values of several genetic statistics such as mean number of alleles per locus, proportion of loci polymorphic, and observed heterozygosity, are significantly lower than populations of any of 17 other sexual species of Antennaria that have been studied previously. It is likely that the unusual disjunct and restricted distribution of A. arcuata is partially the result of its unusual ecology, as it occurs in moist basins having high concentrations of salts that are frequently disturbed by large grazing animals. Canonical correspondence analysis shows strong relationships between several edaphic, environmental, and geographic features and the genetic variation in the populations. The migration of A. arcuata to other regions since the end of the Wisconsinan might have been inhibited by the fact that suitable habitats occur as small isolated islands in a sea of inhospitable terrain, the dry sagebrush steppe.     

Population differentiation and recombination in wheat scab populations of Gibberella zeae from the United States

In limited previous studies of the Ascomycete fungus Gibberella zeae in North America, the populations examined were genetically and phenotypically diverse and could be viewed as subsamples of a larger population. Our objective in this study was to test the hypothesis that a homogeneous, randomly mating population of G. zeae is contiguous throughout the central and eastern United States across a span of several years. We analysed presence/absence alleles based on amplified fragment length polymorphisms (AFLPs) at 30 loci, 24 of which are defined genetically on a linkage map of G. zeae, from > 500 isolates in eight field populations from seven states collected during the 1998, 1999 and 2000 cropping seasons. All these strains had AFLP profiles similar to those of standard isolates of G. zeae phylogenetic lineage 7. All the populations are genetically similar, have high genotypic diversity and little or no detectable genetic disequilibrium, and show evidence of extensive interpopulation genetic exchange. Allele frequencies in some of the populations examined are not statistically different from one another, but others are. Thus, the populations examined are not mere subsamples from a single, large, randomly mating population. Geographic distance and genetic distance between populations are correlated significantly. The observed differences are relatively small, however, indicating that while genetic isolation by distance may occur, genetic exchange has occurred at a relatively high frequency among US populations of G. zeae. We think that these differences reflect the time required for the alleles to diffuse across the distances that separate them, because relatively little linkage disequilibrium is detected either in the population as a whole or in any of the individual subpopulations.     

The spatial genetic structure of the White‐banded Tanager (Aves,Passeriformes) in fragmented Neotropical savannas suggests two evolutionarily significant units

Understanding the genetic structure of a species is crucial for evolutionary biology research and species conservation. The objectives of this study were to investigate the genetic structure of Neothraupis fasciata in Brazilian savannas and to assess genetic differentiation of its disjunct population in the Amazonian savannas of the state of Amapá. Population genetic structure was assessed in relation to isolation by distance and landscape variables connected with habitat heterogeneity. The influences of factors, such as habitat fragmentation and core–periphery distribution, on genetic diversity were also examined. Data were derived from a set of microsatellite loci of adult individuals from nine localities: eight distributed across the Cerrado and one in the disjunct Amazonian savanna of Amapá. Analysis revealed moderate genetic diversity and moderate population genetic structure, with at least two genetic clusters, one of which is represented exclusively by the disjunct Amapá population. The genetic structure found is not the result of significant influences by geographical distance, habitat heterogeneity, or the core–periphery effect, nor by intense biome fragmentation due to anthropic action. The disjunct Amapá population exhibited a moderate level of genetic differentiation compared to the Cerrado population, suggesting that both can be considered distinct evolutionarily significant units for conservation purposes. Abstract in Portuguese is available with online material.     

Limiting inbreeding in disjunct and isolated populations of a woody shrub

Pollen movements and mating patterns are key features that influence population genetic structure. When gene flow is low, small populations are prone to increased genetic drift and inbreeding, but naturally disjunct species may have features that reduce inbreeding and contribute to their persistence despite genetic isolation. Using microsatellite loci, we investigated outcrossing levels, family mating parameters, pollen dispersal, and spatial genetic structure in three populations of Hakea oldfieldii, a fire‐sensitive shrub with naturally disjunct, isolated populations prone to reduction in size and extinction following fires. We mapped and genotyped a sample of 102 plants from a large population, and all plants from two smaller populations (28 and 20 individuals), and genotyped 158–210 progeny from each population. We found high outcrossing despite the possibility of geitonogamous pollination, small amounts of biparental inbreeding, a limited number of successful pollen parents within populations, and significant correlated paternity. The number of pollen parents for each seed parent was moderate. There was low but significant spatial genetic structure up to 10 m around plants, but the majority of successful pollen came from outside this area including substantial proportions from distant plants within populations. Seed production varied among seven populations investigated but was not correlated with census population size. We suggest there may be a mechanism to prevent self‐pollination in H. oldfieldii and that high outcrossing and pollen dispersal within populations would promote genetic diversity among the relatively small amount of seed stored in the canopy. These features of the mating system would contribute to the persistence of genetically isolated populations prone to fluctuations in size.     

Genetic variation and population structure in Korean populations of eurya japonica (Theaceae)

We investigated levels of genetic diversity, population genetic structure, and gene flow in Eurya japonica, a widespread and broad-leaved evergreen dioecious tree native to Japan, China, Taiwan, and the southern and southwestern coast of the Korean Peninsula. Starch-gel electrophoresis was conducted on leaves collected from 1,000 plants in 20 Korean populations. All 12 loci examined were polymorphic in at least one population, and the mean number of alleles per locus was 3.79. In addition, mean observed population heterozygosity (Ho_p = 0.425), expected heterozygosity (He_p = 0.462), and total genetic diversity (H_T = 0.496) were substantially higher than average values for species with similar life history traits. Although significant differences in allele frequency were detected between populations at all loci (P < 0.001), <7% of the genetic variation was found among populations (F_ST = 0.069). There was a significant negative correlation between genetic identity and distance between populations (r = -0.341; P < 0.05), but this explained only a small amount of the diversity among populations. Indirect estimates of the number of migrants per generation (Nm) (3.37, calculated from F_ST; 3.74, calculated from the mean frequency of eight private alleles) indicate that gene flow is extensive among Korean populations of E. japonica. Factors contributing to the high levels of genetic diversity found within populations of E. japonica include large and contiguous populations, obligating outcrossing (dioecious plant), high fecundity, and long generation time. Occasional seed dispersal by humans and pollen movement by domesticated honey bees may further enhance gene flow within the species.