The role of disjunction and postglacial population expansion on phylogeographical history and genetic diversity of the circumboreal plant Chamaedaphne calyculata

In the last decade a number of studies has illustrated quite different phylogeographical patterns amongst plants with a northern present‐day geographical distribution, spanning the entire circumboreal region and/or circumarctic region and southern mountains. These works, employing several marker systems, have brought to light the complex evolutionary histories of this group. Here I focus on one circumboreal plant species, Chamaedaphne calyculata (leatherleaf), to unravel its phylogeographical history and patterns of genetic diversity across its geographical range. A survey of 29 populations with combined analyses of chloroplast DNA (cpDNA), internal transcribed spacer (ITS) and AFLP markers revealed structuring into two groups: Eurasian/north‐western North American, and north‐eastern North American. The present geographical distribution of C. calyculata has resulted from colonization from two putative refugial areas: east Beringia and south‐eastern North America. The variation of chloroplast DNA (cpDNA) and ITS sequences strongly indicated that the evolutionary histories of the Eurasian/north‐western North American and the north‐eastern North American populations were independent of each other because of a geographical disjunction in the distribution area and ice‐sheet history between north‐eastern and north‐western North America. Mismatch analysis using ITS confirmed that the present‐day population structure is the result of rapid expansion, probably since the last glacial maximum. The AFLP data revealed low genetic diversity of C. calyculata (P = 19.5%, H = 0.085) over the whole geographical range, and there was no evidence of loss of genetic diversity within populations in the continuous range, either at the margins or in formerly glaciated and nonglaciated regions. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 105 , 761–775.     

A rangewide herbarium‐derived dataset indicates high levels of gene flow in black cherry (Prunus serotina)

Isolation by Distance (IBD) is a genetic pattern in which populations geographically closer to one another are more genetically similar to each other than populations which are farther apart. Black cherry (Prunus serotina Ehrh.) (Rosaceae) is a forest tree species widespread in eastern North America, and found sporadically in the southwestern United States, Mexico, and Guatemala. IBD has been studied in relatively few North American plant taxa, and no study has rigorously sampled across the range of such a widespread species. In this study, IBD and overall genetic structure were assessed in eastern black cherry (P. serotina Ehrh. var. serotina), the widespread variety of eastern North America. Eastern North America. Prunus serotina Ehrh. var. serotina (Rosaceae). Dense sampling across the entire range of eastern black cherry was made possible by genotyping 15 microsatellite loci in 439 herbarium samples from all portions of the range. Mantel tests and STRUCTURE analyses were performed to evaluate the hypothesis of IBD and genetic structure. Mantel tests demonstrated significant but weak IBD, while STRUCTURE analyses revealed no clear geographic pattern of genetic groups. The modest geographic/genetic structure across the eastern black cherry range suggests widespread gene flow in this taxon. This is consistent with P. serotina's status as a disturbance‐associated species. Further studies should similarly evaluate IBD in species characteristic of low‐disturbance forests.     

Genetic Variation in Chinese Pine (Pinus tabulaeformis), a Woody Species Endemic to China

Random amplified polymorphic DNA markers were used to investigate genetic variation of the Chinese pine (Pinus tabulaeformis Carr.), a species endemic to China and the most widely distributed pine species in North China. The results revealed that P. tabulaeformis populations had a relatively high level of genetic diversity (H _t = 0.3268), distributed mainly within (79.2%) rather than among (20.8%) populations. The populations of Lingkong Mountain and Wuling Mountain had a higher level of diversity (0.2687) than the other four populations (0.2537). No statistically significant relationships were found between genetic diversity and climatic factors by correlation analysis and between genetic distance and geographic distance by the Mantel test. These results suggest that the partitioning of genetic diversity in each population might have been influenced not only by water and temperature conditions but also by other factors such as human activities and the Holocene postglacial history of these populations.     

Genetic variation in lowland and mountain populations of Tofieldia calyculata and their ability to survive within low levels of genetic diversity

Loss of genetic diversity is expected to be a reason behind the decline of populations of many rare species. To what extent this is true for populations at the range periphery remains to be explored. Alpine species with peripheral lowland populations are an ideal but little-known model system to address this issue. We used 17 microsatellite markers to investigate the genetic diversity and structure of populations of Tofieldia calyculata, a common species in central European mountains, but highly endangered in lowlands. We showed that lowland populations have lower genetic diversity than mountain populations and that the two groups of populations are not clearly differentiated genetically. The species probably survived the last glaciation in refugia in the margins of the Alps and the western Carpathians and some lowland populations likely originated by postglacial colonisation. Some lowland populations may be relictual, but our data did not unequivocally confirm this. Low genetic diversity of lowland populations is likely the result of the reduction of population sizes, limited gene flow, and selfing. Based on data from herbarium specimens from extinct lowland populations, within-population genetic diversity has not changed over the last century suggesting that, under suitable habitat conditions, these populations are able to survive with low levels of genetic diversity. This idea is also supported by the presence of large viable extant populations with very low genetic diversity. Comparisons between modern and historic collection also showed that a large proportion of genetic diversity was lost, due mainly to the extinction of whole populations. Our results provided detailed insight into the recent past of the populations of Tofieldia calyculata, but the genetic diversity of the populations before the twentieth century remains unknown due to the poor quality of old DNA from herbaria samples. Overall, the study indicates that despite reduced genetic diversity, the lowland populations harbour some unique alleles and, with the current levels of genetic diversity, have a chance to survive in the long-term, and thus deserve conservation.

     

Assessment of Genetic Diversity and Population Genetic Structure of Corylus mandshurica in China Using SSR Markers

Corylus mandshurica, also known as pilose hazelnut, is an economically and ecologically important species in China. In this study, ten polymorphic simple sequence repeat (SSR) markers were applied to evaluate the genetic diversity and population structure of 348 C. mandshurica individuals among 12 populations in China. The SSR markers expressed a relatively high level of genetic diversity (Na = 15.3, Ne = 5.6604, I = 1.8853, Ho = 0.6668, and He = 0.7777). According to the coefficient of genetic differentiation (F _st = 0.1215), genetic variation within the populations (87.85%) were remarkably higher than among populations (12.15%). The average gene flow (Nm = 1.8080) significantly impacts the genetic structure of C. mandshurica populations. The relatively high gene flow (Nm = 1.8080) among wild C. mandshurica may be caused by wind-pollinated flowers, highly nutritious seeds and self-incompatible mating system. The UPGMA (unweighted pair group method of arithmetic averages) dendrogram was divided into two main clusters. Moreover, the results of STRUCTURE analysis suggested that C. mandshurica populations fell into two main clusters. Comparison of the UPGMA dendrogram and the Bayesian STRUCTURE analysis showed general agreement between the population subdivisions and the genetic relationships among populations of C. mandshurica. Group I accessions were located in Northeast China, while Group II accessions were in North China. It is worth noting that a number of genetically similar populations were located in the same geographic region. The results further showed that there was obvious genetic differentiation among populations from Northeast China to North China. Results from the Mantel test showed a weak but still significant positive correlation between Nei’s genetic distance and geographic distance (km) among populations (r = 0.419, P = 0.005), suggesting that genetic differentiation in the 12 C. mandshurica populations might be related to geographic distance. These data provide comprehensive information for the development of conservation strategies of these valuable hazelnut resources.     

Phylogeography and genetic structure of disjunct Salix arbutifolia populations in Japan

Disjunct geographic distributions of boreal plant species at the southern edges of their ranges are expected to result in low genetic diversity and high genetic differentiation in the disjunct populations. This prediction was tested in a riparian willow, Salix arbutifolia, distributed in the northeastern Eurasian continent and the Sakhalin, Hokkaido, and Honshu Islands, using chloroplast DNA haplotypes and nuclear microsatellite genotypes. Hokkaido and Honshu populations shared a chloroplast haplotype identical to a closely related species, S. cardiophylla. This haplotype was divergent from haplotypes in the Eurasian continent (Primorsky) and the Sakhalin Island. In the nuclear microsatellites, most Hokkaido populations were genetically closer to Primorsky populations than to Sakhalin populations in spite of the geographical vicinity between Sakhalin and Hokkaido. The unexpected genetic divergence between Sakhalin and Hokkaido implies a complicated history of migration and colonization. The most peripheral populations in Honshu had the lowest genetic diversity and were most differentiated from the others. Thus, low genetic diversity and high genetic differentiation at the range periphery suggest substantial effects of genetic drift on genetic structure in the disjunct populations of Salix arbutifolia at the southern edge of its range.     

High genetic diversity declines towards the geographic range periphery of Adonis vernalis,a Eurasian dry grassland plant

Genetic diversity is important for species' fitness and evolutionary processes but our knowledge on how it varies across a species' distribution range is limited. The abundant centre hypothesis (ACH) predicts that populations become smaller and more isolated towards the geographic range periphery – a pattern that in turn should be associated with decreasing genetic diversity and increasing genetic differentiation. We tested this hypothesis in Adonis vernalis, a dry grassland plant with an extensive Eurasian distribution. Its life‐history traits and distribution characteristics suggest a low genetic diversity that decreases and a high genetic differentiation that increases towards the range edge. We analysed AFLP fingerprints in 28 populations along a 4698‐km transect from the geographic range core in Russia to the western range periphery in Central and Western Europe. Contrary to our expectation, our analysis revealed high genetic diversity (range of proportion of polymorphic bands = 56–81%, He = 0.168–0.238) and low genetic differentiation across populations (Φ_ST = 0.18). However, in congruence with the genetic predictions of the ACH, genetic diversity decreased and genetic differentiation increased towards the range periphery. Spanish populations were genetically distinct, suggesting a divergent post‐glacial history in this region. The high genetic diversity and low genetic differentiation in the remaining A. vernalis populations is surprising given the species' life‐history traits and points to the possibility that the species has been widely distributed in the studied region or that it has migrated from a diverse source in an East–West direction, in the past.     

Genetic diversity of SSR markers in wild populations of Tapiscia sinensis,an endangered tree species

Tapiscia sinensis is a Tertiary relict and endangered tree species with unique scientific research value and great economic value. In this study, we assessed the genetic diversity of five wild T. sinensis populations from different geographical regions using 10 polymorphic simple sequence repeat (SSR) markers. Our results reveal that the natural populations of T. sinensis have rich genetic diversity (PPL = 100%, He = 0.6904, I = 1.4368), with Shannon's index indicating that the T. sinensis populations are at a relatively stable stage. Of the genetic relationships among populations, the distance between the Hunan Yanling (YL) and Guizhou Xifeng (XF) populations is the smallest (0.4829); the genetic distance between the Shaanxi Ningshan (NS) and the Guizhou Xifeng (XF) populations is the largest (0.9821). A Mantel test shows that there is no correlation among the populations between geographic distance and genetic distance. AMOVA suggest that 33.3% of the genetic variation arose among the populations, while 66.7% of the variation arose within them. The moderate gene flow among populations (Nm = 0.7274) is not sufficient to counteract genetic drift within the populations and result in significant differentiation (Fst = 0.2987). Our results will benefit the conservation and exploitation of T. sinensis and provide a theoretical basis for further study of the evolution and phylogeography of the species.     

Genetic diversity of wild populations of Rheum tanguticum endemic to China as revealed by ISSR analysis

Rheum tanguticum is an important but endangered traditional Chinese medicine endemic to China. The wild resources have been declining. Establishing the genetic diversity of the species would assist in its conservation and breeding program. Inter-simple sequence repeats (ISSR) markers were used to assess the genetic diversity and population genetic structure in 13 wild populations of R. tanguticum from Qinghai Province. Thirteen selected primers produced 329 discernible bands, with 326 (92.94%) being polymorphic, indicating high genetic diversity at the species level. The Nei's gene diversity (He) was estimated to be 0.1724 within populations (range 0.1026–0.2104), and 0.2689 at the species level. Analysis of molecular variance (AMOVA) showed that the genetic variation was found mainly within populations (71.02%), but variance among populations was only 28.98%. In addition, Nei's differentiation coefficients (G_st) was found to be high (0.3585), confirming the relatively high level of genetic differentiation among populations. Mantel test revealed a significant correlation between genetic and geographic distances (r = 0.573, P = 0.002), and the unweighted pair-group method using arithmetic average (UPGMA) clustering and Principal coordinates analysis (PCoA) demonstrated similar results. Meanwhile, the genetic diversity of R. tanguticum positively correlated with altitude and annual mean precipitation, but negatively correlated with latitude and annual mean temperature. This result might be an explanation that the natural distribution of R. tanguticum is limited to alpine cold areas. We propose conservation strategy and breeding program for this plant.     

High genetic diversity detected in the endemic Primula apennina Widmer (Primulaceae) using ISSR fingerprinting

Primula apennina Widmer is endemic to the North Apennines (Italy). ISSR were used to detect the genetic diversity within and among six populations representative of the species distribution range. High levels of genetic diversity were revealed both at population percentage of polymorphic band (PPB = 75.92%, H _S = 0.204, H _pop = 0.319) and at species level (PPB = 96.95%, H _T = 0.242, H _sp = 0.381). Nei gene diversity statistics (15.7%), Shannon diversity index (16.3%) and AMOVA (14%) detected a moderate level of interpopulation diversity. Principal coordinate and Bayesian analyses clustered the populations in three major groups along a geographic gradient. The correlation between genetic and geographic distances was positive (Mantel test, r = 0.232). All together, these analyses revealed a weak but significant spatial genetic structure in P. apennina, with gene flow acting as a homogenizing force that prevents a stronger differentiation of populations. Conservation measures are suggested based on the observed pattern of genetic variability.     

Genetic diversity and relationships among wild and cultivated Stenocereus queretaroensis populations in western Mexico

Stenocereus queretaroensis is an endemic, chiropterophilous, columnar cactus of economic importance in Mexico. To investigate the effect of artificial selection on genetic diversity, inter-simple sequence repeat (ISSR) markers were used to estimate the genetic variation of wild, orchard, and backyard populations of S. queretaroensis from two regions in western Mexico. Six primers were used to generate 62 bands, of which 39 were polymorphic (62.9%). The total genetic diversity was similar in the wild (H_T = 0.296) and orchard (H_T = 0.291) groups, and slightly lower in the backyard group (H_T = 0.281). Wild populations (F_ST = 0.13) were less differentiated than backyard (F_ST = 0.17) and orchard (F_ST = 0.21) populations. The wild and backyard groups were genetically closer (0.015) than the wild and orchard (0.018) groups. A Mantel test revealed a positive correlation between genetic and geographic distances (r = 0.433, p = 0.002). In conclusion, gene flow and the prevailing management system have efficiently maintained genetic diversity and facilitated inter-population differentiation in S. queretaroensis.     

Genetic variability and phylogeographical patterns of a nonindigenous species invasion: a comparison of exotic vs. native zebra and quagga mussel populations

There have been few investigations of the number of founding sources and amount of genetic variability that lead to a successful nonindigenous species invasion, although genetic diversity is believed to play a central role. In the present study, population genetic structure, diversity and divergence patterns were analysed for the zebra mussel Dreissena polymorpha [n=280 samples and 63 putative randomly amplified polymorphic DNA (RAPDs) gene loci] and the quagga mussel D. bugensis (n=136 and 52 loci) from 10 nonindigenous North American and six Eurasian sampling sites, representing their present‐day ranges. Results showed that exotic populations of zebra and quagga mussels had surprisingly high genetic variability, similar to those in the Eurasian populations, suggesting large numbers of founding individuals and consistent with the hypothesis of multiple colonizations. Patterns of genetic relationships indicate that the North American populations of D. polymorpha likely were founded by multiple source populations from north‐western and northcentral Europe, but not from southcentral or eastern Europe. Sampling areas within North America also were significantly divergent, having levels of gene flow and migration about twice those separating long‐established Eurasian populations. Samples of D. bugensis in Lakes Erie and Ontario were significantly different, with the former being more closely related to a native population from the Dnieper River, Ukraine. No evidence for a founder effect was discerned for either species.     

Isolation by distance and gene flow in the Eurasian badger (Meles meles) at both a local and broad scale

Eurasian badgers, Meles meles, have been shown to possess limited genetic population structure within Europe; however, field studies have detected high levels of philopatry, which are expected to increase population structure. Population structure will be a consequence of both contemporary dispersal and historical processes, each of which is expected to be evident at a different scale. Therefore, to gain a greater understanding of gene flow in the badger, we examined microsatellite diversity both among and within badger populations, focusing on populations from the British Isles and western Europe. We found that while populations differed in their allelic diversity, the British Isles displayed a similar degree of diversity to the rest of western Europe. The lower genetic diversity occurring in Ireland, Norway and Scotland was more likely to have resulted from founder effects rather than contemporary population density. While there was significant population structure (F ST = 0.19), divergence among populations was generally well explained by geographic distance (P < 0.0001) across the entire range studied of more than 3000 km. Transient effects from the Pleistocene appear to have been replaced by a strong pattern of genetic isolation by distance across western Europe, suggestive of colonization from a single refugium. Analysis of individuals within British populations through Mantel tests and spatial autocorrelation demonstrated that there was significant local population structure across 3-30 km, confirming that dispersal is indeed restricted. The isolation by distance observed among badger populations across western Europe is likely to be a consequence of this restricted local dispersal.     

Genetic diversity of the threatened Chinese endemic plant,Sinowilsonia henryi Hemsi. (Hamamelidaceae), revealed by inter-simple sequence repeat (ISSR) markers

Sinowilsonia henryi Hemsi., the only representative of the monotypic genus Sinowilsonia Hemsi. (Hamamelidaceae), is a threatened plant endemic to China with high phylogenetical, ecological and economical values. In the present study, inter-simple sequence repeat (ISSR) markers were employed to investigate the genetic diversity and differentiation of 214 individuals sampled from 14 populations. Fifteen selected primers yielded a total of 178 bright and discernible bands. The genetic diversity was low at the population level (h = 0.1025; I = 0.1506; PPL = 26.7%), but quite high at the species level (h = 0.2449; I = 0.3690; PPL = 72.5%). In line with the limited gene flow (N_m = 0.3537), the hierarchical analysis of molecular variance (AMOVA) revealed pronounced genetic differentiation among populations (Φ_ST = 0.6639). Furthermore, the Mantel test revealed a significant correlation between genetic and geographic distances among populations (r = 0.688, P = 0.001), indicating the role of geographic isolation in shaping its present population genetic structure. The present patterns of genetic diversity of S. henryi were assumed to result largely from its evolutionary history and geographic factors. Based on these findings, conservation strategies were proposed to preserve this threatened plant.     

Genetic structure of Rhamnus glaucophylla Sommier endemic to Tuscany

Rhamnus glaucophylla Sommier is an endemic small tree or shrub belonging to sect. Eurhamnus. It grows on cliffs of the Apuan Alps and of the Lucca Apennine in Tuscany (Italy). ISSRs were used to detect the genetic diversity within and among five populations representative of the species distribution range. Moderate levels of genetic diversity were revealed as percentage of polymorphic band (PPB) both at the population (PPB?=?22.63%, H _S?=?0.0801, Sh?=?0.1193) and species level (PPB?=?48.68%, H _T?=?0.1155, Sh?=?0.1837). The correlation between genetic and geographic distances was not significant (Mantel test, r?=?0.17; P?<?0.26). The information on the pattern of genetic variation obtained in this work bears important implications for conservation management, and in particular for ex situ conservation programmes involving long-term seed storage in seed banks.     

Genetic Diversity and Population Structure in Polygonum cespitosum: Insights to an Ongoing Plant Invasion

Molecular markers can help elucidate how neutral evolutionary forces and introduction history contribute to genetic variation in invaders. We examined genetic diversity, population structure and colonization patterns in the invasive Polygonum cespitosum, a highly selfing, tetraploid Asian annual introduced to North America. We used nine diploidized polymorphic microsatellite markers to study 16 populations in the introduced range (northeastern North America), via the analyses of 516 individuals, and asked the following questions: 1) Do populations have differing levels of within-population genetic diversity? 2) Do populations form distinct genetic clusters? 3) Does population structure reflect either geographic distances or habitat similarities? We found low heterozygosity in all populations, consistent with the selfing mating system of P. cespitosum. Despite the high selfing levels, we found substantial genetic variation within and among P. cespitosum populations, based on the percentage of polymorphic loci, allelic richness, and expected heterozygosity. Inferences from individual assignment tests (Bayesian clustering) and pairwise F _ST values indicated high among-population differentiation, which indicates that the effects of gene flow are limited relative to those of genetic drift, probably due to the high selfing rates and the limited seed dispersal ability of P. cespitosum. Population structure did not reflect a pattern of isolation by distance nor was it related to habitat similarities. Rather, population structure appears to be the result of the random movement of propagules across the introduced range, possibly associated with human dispersal. Furthermore, the high population differentiation, genetic diversity, and fine-scale genetic structure (populations founded by individuals from different genetic sources) in the introduced range suggest that multiple introductions to this region may have occurred. High genetic diversity may further contribute to the invasive success of P. cespitosum in its introduced range.     

Genetic variation and population differentiation of the endochitinase gene family in Pinus monticola

In the present study, we characterized nucleotide variations of the Pinus monticola class IV endochitinase (PmCh4) family. Using primers targeting at conserved amino acid motifs of plant class IV endochitinases, genomic DNA was amplified. Sequence data analysis identified five novel genes in the PmCh4 family with one pseudogene. Single nucleotide polymorphisms of the PmCh4 family were surveyed in seven open-pollinated seed lots representing diverse geographical distribution. Variable levels of average pairwise nucleotide diversity (π = 0.00422–0.02079) and relatively high levels of haplotype diversity (H _d = 0.85–0.96) were revealed at PmCh4 loci. Based on nucleotide variation, P. monticola populations were clustered into two main groups by phylogenetic analysis based on Nei’s genetic distance. The Mantel test revealed no correlation between geographical and genetic distances (r = ?0.11, P = 0.59). A further SNP genetic diversity study on more P. monticola populations throughout Western North America may help the design of sampling regimes for tree breeding, genetic conservation and assisted migration under climate change.     

Quaternary climate instability is correlated with patterns of population genetic variability in Bombus huntii

Climate oscillations have left a significant impact on the patterns of genetic diversity observed in numerous taxa. In this study, we examine the effect of Quaternary climate instability on population genetic variability of a bumble bee pollinator species, Bombus huntii in western North America. Pleistocene and contemporary B. huntii habitat suitability (HS) was estimated with an environmental niche model (ENM) by associating 1,035 locality records with 10 bioclimatic variables. To estimate genetic variability, we genotyped 380 individuals from 33 localities at 13 microsatellite loci. Bayesian inference was used to examine population structure with and without a priori specification of geographic locality. We compared isolation by distance (IBD) and isolation by resistance (IBR) models to examine population differentiation within and among the Bayesian inferred genetic clusters. Furthermore, we tested for the effect of environmental niche stability (ENS) on population genetic diversity with linear regression. As predicted, high‐latitude B. huntii habitats exhibit low ENS when compared to low‐latitude habitats. Two major genetic clusters of B. huntii inhabit western North America: (a) a north genetic cluster predominantly distributed north of 28°N and (b) a south genetic cluster distributed south of 28°N. In the south genetic cluser, both IBD and IBR models are significant. However, in the north genetic cluster, IBD is significant but not IBR. Furthermore, the IBR models suggest that low‐latitude montane populations are surrounded by habitat with low HS, possibly limiting dispersal, and ultimately gene flow between populations. Finally, we detected high genetic diversity across populations in regions that have been climatically unstable since the last glacial maximum (LGM), and low genetic diversity across populations in regions that have been climatically stable since the LGM. Understanding how species have responded to climate change has the potential to inform management and conservation decisions of both ecological and economic concerns.     

Genetic diversity and structure of natural Pinus tabulaeformis populations in North China using amplified fragment length polymorphism (AFLP)

Chinese pine (Pinus tabulaeformis carr.), endemic to China, is a conifer species with extensive and fragmented distribution in North China. In this study, the genetic diversity and structure of 20 natural populations of this species were investigated using amplified fragment length polymorphism (AFLP) markers. A total of 445 fragments were revealed with 8 pairs of primers, 379 (85.17%) of which were polymorphic. A moderate level of genetic diversity was detected at the species level (Shannon's information index I = 0.356, Nei's gene diversity H_E = 0.271) and at the population level (I = 0.219, H_E = 0.206). Most of genetic variation was within populations while a considerable level of genetic differentiation was detected (G_ST = 0.352, Ф_ST = 0.304). The high differentiation could be attributed to the complex and fragmented habitats, and a limited gene flow among populations (N_m = 0.572). The Mantel test indicated that there was significant correlation (r = 0.455, P < 0.001) between Nei's genetic distance and geographical distance among all the populations. The results suggested that proper countermeasures should be taken to prevent the habitat further deterioration and maintain the genetic diversity of this species.     

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.