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.     

Mating system and genetic differentiation inDasypyrum villosum (Poaceae) in Italy

Genetic differentiation at the morphological, isozyme, and DNA levels among sevenDasypyrum villosum (Poaceae, Triticeae, 2n = 14, VV genomes) populations from Italy was studied. A measure of the mating system was also obtained. Genetic diversity was mainly distributed within populations (90%) rather than among populations (10%), typical for most allogamous species. Interpopulation diversity, however, was greatest between the most geographically distant populations (about 750 km apart, 911 m altitude difference). The mating system was estimated to vary from 55 to 100% outcrossing. One population (I-16, Bomarzo) deviated from the others in its uniform early flowering habit and presence of isozyme alleles not found in other populations. It had genetic diversity similar to other populations for isozyme (Got-V2, Got-V3, andEst-VF) and ribosomal RNA (Nor-Vl) loci. This population is believed to be the product of a few migrant founder seeds and its unique characters point out that generalized population biology parameters of genetic diversity are not sufficient for describing species variation nor for developing conservation strategies.     

Wheat storage proteins: diversity of HMW glutenin subunits in wild emmer from Israel

Summary The diversity of HMW glutenin subunits in the tetraploid wild progenitor of wheat, Triticum turgidum var. dicoccoides was studied electrophoretically in 231 individuals representing 11 populations of wild emmer from Israel. The results show that (a) The two HMW glutenin loci, Glu-A1 and Glu-B1, are rich in variation, having 11 and 15 alleles, respectively, (b) Genetic variation in HMW glutenin subunits is often severely restricted in individual populations, supporting an island population genetic model, (c) Significant correlations were found between glutenin diversity and the frequencies of specific glutenin alleles and physical (climate and soil) and biotic (vegetation) variables. Our results suggest that: (a) at least part of the glutenin polymorphisms in wild emmer can be accounted for by environmental factors and (b) the endosperm of wild emmer contains many allelic variants of glutenin storage proteins that are not present in bread wheat and could be utilized in breeding varieties with improved bread-making qualities.     

Allozyme diversity in the federally threatened golden paintbrush, <Emphasis Type="Italic">Castilleja levisecta</Emphasis> (Scrophulariaceae)

Castilleja levisecta (Scrophulariaceae), the golden paintbrush, is an insect-pollinated herbaceaous perennial found in the Pacific Northwest. Currently restricted to two island populations off British Columbia and nine populations (eight on islands) in Washington, C. levisecta is a rare species threatened with extinction. Allozymes were used to describe genetic diversity and structure in these eleven populations. Despite its threatened status and small geographic range, exceptionally high levels of genetic diversity are maintained within C. levisecta. All sixteen of the loci resolved were polymorphic within the species (P_s=100%), while the mean percentage of loci polymorphic within populations (P_p) was 65.7%. The mean number of alleles per polymorphic locus (AP_s) was 2.94 within the species and averaged 2.38 within populations (AP_p). Genetic diversity (H_es) was 0.285 for the species, whereas mean population genetic diversity (H_ep) was 0.213. Smaller populations had, on average, fewer observed alleles and less genetic diversity. A significant negative correlation (r = –0.72) was found between genetic identity and geographic distance, indicating reduced gene flow between distant populations. The most geographically isolated population was one of the larger populations, one of the most genetically diverse and the most genetically divergent. A wide range of pairwise population genetic identities (I = 0.771 – 0.992) was found, indicating considerable genetic divergence between some populations. Overall, 19% of the total genetic diversity was distributed among populations. Results of this survey indicate that genetic augmentation of existing populations is unnecessary. The high allelic diversity found for the species and within its populations holds promise for conservation and restoration efforts to save this rare and threatened plant species.     

Geographic variation and dispersal history in Fennoscandian populations of two forest herbs

 Carex digitata and Melica nutans are forest understorey herbs with wide European distributions and their northern range margins in Fennoscandia. The species have closely similar habitat requirements, occur in small populations in old forest stands on base-rich to neutral soils and have restricted dispersal abilities at the present day. This study investigates the structure of allozyme variation (12 and 8 loci, respectively) in material of both species (38 and 37 populations, respectively) from throughout southern Sweden and southern Finland. Both species show a relatively low overall genetic diversity (H_T excluding monomorphic loci=0.17 and 0.18, respectively). The hierarchic structuring of allelic diversity in the species is similar, with a relatively high between-population component of diversity (G_ST=0.36 and 0.37, respectively). Neither of the species shows a clear intraspecific pattern of geographic differentiation. The lack of large-scale patterns of geographic differentiation is not consistent with a simple scenario of discrete and independent waves of immigration into Fennoscandia. However, particularly in M. nutans, a group of populations from a lowland belt across southwestern Finland and southern central Sweden is somewhat differentiated from populations to the north and south. A number of rare alleles in both species are widely, but patchily distributed in low frequencies. Hybridization may account for the scattered occurence of some of the rare alleles in Carex digitata, but cannot explain the distribution of rare alleles in Melica nutans. Received July 23, 2001 Accepted December 6, 2001     

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.     

Storage-protein variation in wild emmer wheat (Triticum turgidum ssp.dicoccoides) from Jordan and Turkey. I. Electrophoretic characterization of genotypes

Seed storage-protein variation at theGlu-A1,Glu-B1 andGli-B1/Glu-B3 loci in the tetraploid wild progenitor of wheat,T. dicoccoides, was studied electrophoretically in 315 individuals representing nine populations from Jordan and three from Turkey. A total of 44 different HMW-glutenin patterns were identified, resulting from the combination of 15 alleles in the A genome and 19 in the B genome. Twenty-seven new allelic variants, 12 at theGlu-A1 locus and 15 at theGlu-B1 locus, were identified by comparing the mobilities of their subunits to those previously found in bread and durum wheats. The novel variants include six alleles at theGlu-A1 locus showing both x and y subunits. The genes coding for the 1Bx and 1By subunits showed no or very little (3%) inactivity, the 1Ax gene showed a moderate degree (6.3%) of inactivity whereas the gene coding for lAy showed the highest degree of inactivity (84.8%). A high level of polymorphism was also present for the omega- and gamma-gliadins and LMW-glutenin subunits encoded by genes at the linkedGli-B1 andGlu-B3 loci (19 alleles). Some Jordanian accessions were found to contain omega-gliadin 35, gamma-gliadin 45, and LMW-2 also present in cultivated durum wheats and related to good gluten viscoelasticity. The newly-discovered alleles enhance the genetic variability available for improving the technological quality of wheats. Additionally some of them may facilitate basic research on the relationship between industrial properties and the number and functionality of HMW- and LMW-glutenin subunits.     

Genetic biogeography of the rare “copper moss,” Mielichhoferia elongata (Bryaceae)

Mielichhoferia elongata, one of the so-called “copper mosses,” has a broad but highly disjunctive geographic distribution and is rare throughout its range. A genetic analysis of 30 populations based on a survey of 21 allozyme loci reveals the following. 1) Total gene diversity at the specific level is high (0.41). 2) Within-population diversity is low, and over 90% of all genetic variation is among rather than within populations (mean G_ST = 0.93). 3) There is little differentiation in allele frequencies between North American and European populations. 4) Populations consist of one to six multilocus genotypes; 13 of the populations appear to consist of a single clone. 5) Colorado populations contain a tremendous reservoir of genetic variation (88% of all alleles found in the species in North America and Europe occur in one or more Colorado populations). 6) Populations in the eastern and western United States, and in Europe, contain subsets of the allelic diversity found in Colorado. The genetic structure of M. elongata suggests repeated dispersal and founding of populations.     

High-molecular-weight glutenin subunit variation in Turkish emmer wheat [Triticum turgidum L. ssp. dicoccon (Schrank) Thell.] landraces

The genetic diversity of high-molecular-weight (HMW) glutenin subunits in 18 cultivated emmer wheat landrace populations, originating from Turkey, was investigated using sodium dodecyl sulphate polyacrylamide gel electrophoresis. The mean number of alleles (n _a) and effective alleles (n _ea) were observed as 3.67 and 1.53, respectively. The mean values of expected heterozygosity (gene diversity) (H _e) and average heterozygosity (H _e,av) were calculated as 0.31 and 0.12, respectively. Actual genetic differentiation (D) and gene flow (N _m) between the different populations were observed as 0.24 and 0.16, respectively. Statistical analysis of Pearson’s correlation, multiple regressions and principal component analysis indicated that eco-geographical variables have a significant effect on HMW-glutenin diversity. Considering the dramatic decrease in genetic diversity of modern high-yielding cultivars, the conservation of genetic diversity in these wheat landraces, and in other old cultivars, is important for improving modern monocultures and their ability to resist biotic and abiotic conditions caused by climate changes, thus generating a wide adaption to a variety of environmental conditions. Adoptation measures for germplasm conservation of Turkish emmer wheat landraces and utilisation of their germplasm for improvement of modern wheat varieties were discussed in this study.     

Reduced MHC class II diversity in island compared to mainland populations of the black-footed rock-wallaby (<Emphasis Type="Italic">Petrogale lateralis lateralis</Emphasis>)

Many animal populations that are endangered in mainland areas exist in stable island populations, which have the potential to act as an “ark” in case of mainland population declines. Previous studies have found neutral genetic variation in such species to be up to an order of magnitude lower in island compared to mainland populations. If low genetic variation is prevalent across fitness-related loci, this would reduce the effectiveness of island populations as a source of individuals to supplement declining mainland populations or re-establish extinct mainland populations. One such species, the black-footed rock-wallaby (Petrogale lateralis lateralis), exists within fragmented mainland populations and small island populations off Western Australia. We examined sequence variation in this species within a fitness-related locus under positive selection, the MHC class II DAB β1 locus. The mainland populations displayed greater levels of allelic diversity (4–7 alleles) than the island population, despite being small and isolated, and contained at least two DAB gene copies. The island population displayed low allelic diversity (2 alleles) and fewer alleles per individual in comparison to mainland populations, and probably possesses only one DAB gene copy. The patterns of DAB diversity suggested that the island population has a markedly lower level of genetic variation than the mainland populations, in concordance with results from microsatellites (genotyped in a previous study), but preserved unique alleles which were not found in mainland populations. Where possible, conservation actions should pool individuals from multiple populations, not only island populations, for translocation programs, and focus on preventing further declines in mainland populations.     

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.     

Population structure of the olive flounder (Paralichthys olivaceus) in Korea inferred from microsatellite marker analysis

The population structure of olive flounder Paralichthys olivaceus was estimated using nine polymorphic microsatellite (MS) loci in 459 individuals collected from eight populations, including five wild and three hatchery populations in Korea. Genetic variation in hatchery (mean number of alleles per locus, A = 10·2–12·1; allelic richness, A_R = 9·3–10·1; observed heterozygosity, H_O = 0·766–0·805) and wild (mean number of alleles per locus, A = 11·8–19·6; allelic richness, A_R = 10·9–16·1; observed heterozygosity, H_O = 0·820–0·888) samples did not differ significantly, suggesting a sufficient level of genetic variation in these well‐managed hatchery populations, which have not lost a substantial amount of genetic diversity. Neighbour‐joining tree and principal component analyses showed that genetic separation between eastern and pooled western and southern wild populations in Korea was probably influenced by restricted gene flow between regional populations due to the barrier effects of sea currents. The pooled western and southern populations are genetically close, perhaps because larval dispersal may depend on warm currents. One wild population (sample from Wando) was genetically divergent from the main distribution, but it was genetically close to hatchery populations, indicating that the genetic composition of the studied populations may be affected by hydrographic conditions and the release of fish stocks. The estimated genetic population structure and potential applications of MS markers may aid in the proper management of P. olivaceus populations.     

High molecular weight glutenin subunit variation in wild and cultivated einkorn wheats (Triticum spp.,Poaceae)

Variation in high molecular weight (HMW) glutenin subunit composition among wild and cultivated einkorn wheats (2n = 2x = 14, AA) was investigated using one- (SDS-PAGE and urea/SDS-PAGE) and two-dimensional (IEF × SDS-PAGE) electrophoretic analyses. The material comprised 150 accessions ofTriticum urartu, 160 accessions ofT. boeoticum, 24 accessions ofT. boeoticum subsp.thaoudar and 74 accessions of primitive domesticatedT. monococcum from many different germplasm collections. The biochemical characteristics of HMW-glutenin subunits ofT. boeoticum andT. monococcum were highly similar to one another but distinctly different from those ofT. urartu. All the species analysed were characterised by large intraspecific variation and only three HMW-glutenin subunit patterns were identical betweenT. boeoticum andT. monococcum. Consistent with the distinct nature ofT. urartu, all its HMW-glutenin patterns were different from those found inT. boeoticum andT. monococcum. The differences detected between these species might reflect their reproductive isolation and are consistent with recent nomenclatural and biosystematic treatments that recogniseT. urartu as separate species fromT. boeoticum andT. monococcum. The presence of three distinct glutenin components in some accessions of the species studied seems to be evidence for the existence of at least three active genes controlling the synthesis of the HMW-glutenin subunits in the A genome of wild and primitive domesticated diploid wheats. Results indicate also that HMW-glutenin subunits could represent useful markers for the evaluation of genetic variability present in different wild diploid wheat collections and subsequently for their conservation and future utilisation.     

Genetic differentiation and reduced genetic diversity at the northern range edge of two species with different dispersal modes

Theory predicts that genetic variation should be reduced at range margins, but empirical support is equivocal. Here, we used genotyping‐by‐sequencing technology to investigate genetic variation in central and marginal populations of two species in the marine gastropod genus Crepidula. These two species have different development and dispersal types and might therefore show different spatial patterns of genetic variation. Both allelic richness and the proportion of private alleles were highest in the most central populations of both species, and lower at the margin. The species with low dispersal, Crepidula convexa, showed high degrees of structure throughout the range that conform to the pattern found in previous studies using other molecular markers. The northernmost populations of the high‐dispersing species, Crepidula fornicata, are distinct from more central populations, although this species has been previously observed to have little genetic structure over much of its range. Although genetic diversity was significantly lower at the range margin, the absolute reduction in diversity observed with these genomewide markers was slight, and it is not yet known whether there are functional consequences for the marginal populations.     

Genetic diversity in populations of Sphagnum capillifolium from the mountains of Bulgaria,and their possible refugial role

Abstract

Genetic diversity in eight populations of Sphagnum capillifolium from different Bulgarian mountains was investigated by means of isozyme electrophoresis. High levels of allelic diversity were found (H_S = 0.119), comparable to earlier estimates for northern European populations (H_S = 0.116). Strong differentiation among populations and a low number of widespread genotypes suggest a high degree of isolation and restricted gene flow between populations, which is consistent with generally small and scattered populations. The large proportion of distinguishable genotypes (mean 0.498) suggests high levels of out-crossing either currently or in the past. Introgression between S. capillifolium and S. rubellum, a species not found in Bulgaria, was suggested by the occurrence of rubellum-alleles in five populations from different mountains. This could be explained by an ancient hybridization event in a sympatric population. Based on (1) the high genetic diversity, (2) the fairly wide distribution of alien alleles, and (3) the isolated distribution of populations even within one mountain, a possible survival of S. capillifolium in the Balkan area during the Quaternary ice periods is hypothesized.     

Tetranucleotide microsatellite loci from the black bear (Ursus americanus)

We describe primers and polymerase chain reaction conditions to amplify 21 tetranucleotide microsatellite DNA loci in black bears (Ursus americanus). We tested primers using individuals from two populations, one each in Georgia and Florida. Among individuals from Georgia (n = 29), primer pairs yielded an average of 2.9 alleles (range, one to four) and an average observed heterozygosity (H_O) of 0.50 (range, 0.00 to 0.79). Among individuals from Florida (n = 19), primer pairs yielded an average of 5.7 alleles (range, one to 14) and an H_O of 0.55 (range, 0.00 to 1.00). A comparison of previously developed markers with individuals from Georgia suggests that bear populations in Georgia and Florida have reduced allelic diversity relative to other populations.     

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.     

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.     

基于SSR标记探讨三种金花茶植物的遗传多样性和遗传结构

薄叶金花茶、小花金花茶和小瓣金花茶是三种濒危金花茶植物,为了解珍稀濒危植物遗传多样性和遗传结构,该研究利用微卫星标记对他们的7个种群共184个个体进行了遗传多样性和遗传结构分析。结果表明:11个位点共检测到等位基因92个。在物种水平上,小瓣金花茶平均等位基因数(N_A)为3.9、有效等位基因数(N_E)为2.328、观测杂合度(H_o)为0.520、期望杂合度(H_e)为0.501,高于薄叶金花茶和小花金花茶。在种群水平上,有效等位基因数(N_E)在1.788～2.466之间,期望杂合度(H_e)在0.379～0.543之间;种群间遗传分化系数(FST)在0.143 7～0.453 3之间,种群间基因流(N_m)在0.301 5～1.488 9之间。AMOVA分子变异分析显示65.72%的变异存在于种群内。三种金花茶具有较低水平的遗传多样性和高水平的种群间遗传分化。STRUCTURE和PCoA种群遗传结构分析结果将取样种群分为2组,即薄叶金花茶和小花金花茶大部分个体分为一组,小瓣金花茶大部分个体分为一组。现存所有种群应根据实际情况尽快采取就地保护或迁地保护措施。     

Allozyme diversity and genetic structure of marginal and central populations of Corylus avellana L. (Betulaceae) in Europe

Corylus avellana L. (hazel, Betulaceae) is a long-lived, widespread shrub in Europe, having its northern range margin in Fennoscandia and a postglacial history involving range-expansion from refugial areas in southern Europe. In this study, we tested for a relationship between marginality and low within-population genetic diversity by assessing patterns of variation at 14 putatively neutral allozyme loci (comprising 43 putative alleles) within and between 40 natural populations of C. avellana along a north-south transect in Europe. Geographically marginal populations (central Sweden) showed lower levels of within-population diversity than populations in more central regions, as indicated by significant negative correlations between latitude and the percentage of polymorphic loci (r_S=–0.47, P < 0.001), the average number of alleles per locus (r_S=–0.65, P < 0.001), the expected heterozygosity (r_S=–0.19, P < 0.05), and the proportion of distinguishable genotypes (r_S=–0.56, P < 0.001). These patterns, combined with the unusually high between-population component of gene diversity (G_ST=19.7%) and allelic richness (A_ST=24%) in the marginal region, can be attributed to historical bottlenecks during the species postglacial range-expansion, but may also reflect a history of genetic drift in the small, isolated populations occupying the marginal region. Information on the spatial distribution of genotypes provide further support for a role of vegetative reproduction (layering) in the structuring of genetic variation within populations.