AN ELECTROPHORETIC INVESTIGATION OF INTRAGAMETOPHYTIC SELFING IN EQUISETUM ARVENSE

Because homosporous pteridophytes (Psilotophyta, Arthrophyta, most Microphyllophyta and Pteridophyta) produce bisexual gametophytes, it was maintained that high levels of inbreeding would characterize these plants. Electrophoretic evidence was used to estimate the frequency of intragametophytic selfing in Equisetum arvense (Arthrophyta). A total of 669 samples from 17 populations was examined from western North America. Although some populations exhibited as many as seven or eight genotypes, 10 populations were each characterized by only a single genotype; eight of these populations were heterozygous for one or more loci. For most populations, estimates of intragametophytic self-fertilization are 0.000, indicating that virtually all matings involve different gametophytes. Genetic data corroborate predictions based on earlier field and laboratory investigations of Equisetum gametophytes. These detailed studies demonstrated that in many species, including E. arvense, gametophytes are initially either male or female; only later and in the absence of fertilization do some gametophytes become bisexual. Our findings join a growing electrophoretic data base which demonstrates that homosporous pteridophytes are not highly inbreeding as previously suggested.     

Genetic and clonal diversity in Korean populations ofVitex rotundifolia (Verbenaceae)

Vitex rotundifolia L.f. is a woody perennial and has sexual and asexual modes of reproduction. Allozyme study was conducted on 550 plants in 13 Korean populations. The levels of genetic variability and divergence within and among populations, respectively, are considerably lower and higher than the mean values for woody plants with similar life history tralts. Mean percentage of polymorphic loci (P _P), mean number of alleles per locus (A _P), and mean genetic diversity (He _P) within populations ofV. rotundifolia were: 16.7%, 1.21, and 0.047. On average, about 79% of the total variation inV. rotundifolia was common to all populations (meanG _ST=0.208). In addition, significant differences in allele frequencies among populations were found in all polymorphic loci examined (P<0.001). On the other hand, levels of genotypic diversity within and among populations were moderate. About 44% (18/41) of multilocus genotypes were “local genotypes” (genotypes occurring in only one population), whereas only one “widespread genotype” (genotypes occurring in more than 75% of the populations) were detected. The mean number of multilocus genotypes per population (G) and mean genotypic diversity index (D _G) were 8.4 and 0.74, respectively. Most common multilocus genotypes found in populations were homozygous for five polymorphic loci. The abundance of ramets of these genets is responsible for the low levels of expected heterozygosity within populations. The results indicate that clonal reproduction may act as an enhancer of genetic drift by reducing effective size of local populations ofV. rotundifolia.     

THE SIGNIFICANCE OF OUTCROSSING IN AN INTIMATE PLANT-HERBIVORE RELATIONSHIP. I. DOES OUTCROSSING PROVIDE AN ESCAPE FROM HERBIVORES ADAPTED TO THE PARENT PLANT?

Sexual reproduction may be advantageous for hosts that are preyed on or parasitized by enemies that are highly adapted to them. Sexual reproduction can create rare genotypes that may escape predation by virtue of rarity and can create variable progeny that may escape predation if enemies are specialized to only one genotype of host. Populations of the herbivorous thrips, Apterothrips apteris, have been shown to be adapted to individual Erigeron glaucus clones. Here, we show that thrips adapted to the parental clone could better use plant progeny of the “home” clone produced through selfing than progeny derived from selfing of other clones. Thus, despite recombination, progeny produced by selfing presented a resource that was similar to the parental phenotype with respect to use by adapted thrips. We also show that E. glaucus susceptibility to thrips has a genetic basis and then ask whether outcrossing provides a means for E. glaucus clones to escape attack by adapted thrips. When we compared the success of thrips on progeny produced by selfing or outcrossing of the home clone, we found that the merits or disadvantages associated with outcrossing were dependent on the susceptibility to infestation of the parental clones. Selfing by clones characterized by low infestations of thrips appeared to preserve resistant genotypes; all outcrossed progeny had, on average, higher infestation levels than selfed progeny. In contrast, outcrossed progeny of clones characterized by high infestations of thrips had either the same thrips density as progeny from selfing, when the pollen donor was a highly infested clone, or lower density, when the pollen donor was a low infestation clone. The advantages of outcrossing were caused by the alleles contributed to progeny rather than to progeny variability or rarity.     

THE GENETIC STRUCTURE OF LARGE-LAKE DAPHNIA POPULATIONS

Cyclical parthenogenesis allows study of the genetic and evolutionary characteristics of groups exhibiting both asexual and sexual reproduction. The cladoceran genus Daphnia contains species which vary with respect to the relative incidence of sexual reproduction; pond species tend to undergo sexual reproduction more regularly than species found in large lakes. Previous genetic studies have focused on pond populations, generating expectations about large-lake populations that have not been fully met by recent studies. The present study of the Palearctic species Daphnia galeata further examines the genetic structure of large-lake populations. Nine local populations, from lakes in northern Germany, are examined for genetic variation at seven enzyme loci. Populations exhibit similar allelic arrays and often similar allele frequencies at the five polymorphic loci; values of Nei's genetic distance (D) ranged from 0.002 to 0.239, with a mean of 0.084. F_ST values range from 0.012 to 0.257, and spatial autocorrelation coefficients range from -0.533 to 0.551, for the eight alleles analyzed. With few exceptions, within-population genotypic frequencies were in Hardy-Weinberg equilibrium. There was, however, significant heterogeneity in genotypic frequencies among populations. The number of coexisting clonal groups, as determined by three locus genotypes, is high within populations. Clonal groups are widely distributed among localities. The amount of genetic divergence observed among these large-lake populations is smaller than that previously observed among pond populations and suggests that different processes may be important in determining the genetic structure and subsequent phenotypic divergence of lake versus pond populations.     

Consequences of multiple mating‐system shifts for population and range‐wide genetic structure in a coastal dune plant

Evolutionary transitions from outcrossing to selfing can strongly affect the genetic diversity and structure of species at multiple spatial scales. We investigated the genetic consequences of mating‐system shifts in the North American, Pacific coast dune endemic plant Camissoniopsis cheiranthifolia (Onagraceae) by assaying variation at 13 nuclear (n) and six chloroplast (cp) microsatellite (SSR) loci for 38 populations across the species range. As predicted from the expected reduction in effective population size (N_e) caused by selfing, small‐flowered, predominantly selfing (SF) populations had much lower nSSR diversity (but not cpSSR) than large‐flowered, predominantly outcrossing (LF) populations. The reduction in nSSR diversity was greater than expected from the effects of selfing on N_e alone, but could not be accounted for by indirect effects of selfing on population density. Although selfing should reduce gene flow, SF populations were not more genetically differentiated than LF populations. We detected five clusters of nSSR genotypes and three groups of cpSSR haplotypes across the species range consisting of parapatric groups of populations that usually (but not always) differed in mating system, suggesting that selfing may often initiate ecogeographic isolation. However, lineage‐wide genetic variation was not lower for selfing clusters, failing to support the hypothesis that selection for reproductive assurance spurred the evolution of selfing in this species. Within three populations where LF and SF plants coexist, we detected genetic differentiation among diverged floral phenotypes suggesting that reproductive isolation (probably postzygotic) may help maintain the striking mating‐system differentiation observed across the range of this species.     

High genotypic diversity and strong spatial structure in populations of Trifolium alpestre with low seed production

Studies on clonal plants indicate that the proportion between clonal and sexual reproduction can be variable, depending on local habitat conditions and the biological characteristics of the species. In the present study, we assessed this question in Trifolium alpestre by assaying genetic diversity and spatial genotypic structure of natural populations with the use of allozyme markers. Populations revealed high genetic diversity as well as strong spatial structure of multilocus genotypes. The values of genetic diversity were moderately high. Spatially aggregated, identical genotypes spread up to 15 m along linear transects and across 4‐m² plots indicate extensive clonal propagation within populations. However, the existence of numerous unique and small‐sized clones reflects significant contribution from sexual reproduction. Spatially and temporarily stochastic soil disturbances have evidently opened new opportunities for the successful sexual recruitment from the permanent soil seed bank and thus counteracted losses of genetic and genotypic diversity. Seed production in all populations during the three study years was low, in average up to 1.5–2.4 seeds per shoot. The almost total lack of seed set for 57 bagged flower heads on genotypes grown in a common garden indicates that T. alpestre needs pollinators for seed production.     

Selfing versus outcrossing propensity of the fungal pathogen Microbotryumviolaceum across Silenelatifolia host plants

In the fungal pathogen Microbotryumviolaceum mating (i.e. conjugation between cells of opposite mating type) is indispensable for infection of its host plant Silenelatifolia. Since outcrossing opportunities are potentially rare, selfing may be appropriate to ensure reproduction. On the other hand, outcrossing may create genetic variability necessary in the coevolutionary arms race with its host. We investigated the propensity of M. violaceum to outcross vs. self in different host environments. We used haploid sporidia from each of three strains from five fungal populations for pairwise mixtures of opposite mating type, representing either selfing or outcrossing combinations. Mixtures were exposed to leaf extract from seven S. latifolia plants. The proportion of conjugated sporidia quantified mating propensity. The identity of both fungal strains and host influenced conjugation. First, individual strains differed in conjugation frequency by up to 30%, and strains differed in their performance across the different hosts. Second, selfing combinations produced, on average, more conjugations than did outcrossing combinations. Selfing appears to be the predominant mode of reproduction in this fungus, and selfing preference may have evolved as a mechanism of reproductive assurance. Third, individual strains varied considerably in conjugation frequency in selfing and outcrossing combinations across different hosts. This indicates that conjugation between outcrossing partners could be favoured at least in some hosts. Since the dikaryon resulting from conjugation is the infectious unit, conjugation frequency may correspond with infection probability. This assumption was supported by an inoculation experiment, where high infectious sporidial dosage resulted in higher infections success than did low dosage. We therefore predict that sexual recombination can provide this pathogen with novel genotypes able to infect local resistant hosts.     

Micro‐ and macrospatial scale analyses illustrates mixed mating strategies and extensive geneflow in populations of an invasive haploid pathogen

Sexual reproduction in fungi involves either a single individual (selfing) or two individuals (outcrossing). To investigate the roles that these two strategies play in the establishment of an invasive alien pathogen, the Eucalyptus leaf‐infecting fungus, Teratosphaeria (Mycosphaerella) nubilosa was studied. Specifically, the genetic diversity of the pathogen was investigated at micro and macrospatial scales. Interestingly, while data obtained at microspatial scales show clearly that selfing is the main reproductive strategy, at macrospatial scales the population genetic structure was consistent with a genetically outcrossing organism. Additional analyses were performed to explore these apparently discordant results at different spatial scales and to quantify the contribution of selfing vs. outcrossing to the genotypic diversity. The results clearly show that the fungus has a mixed mating strategy. While selfing is the predominant form of mating, outcrosses must have occurred in the pathogen that increased the genotypic diversity of the fungus over time. This mating strategy, coupled with the high levels of geneflow between distant populations of the pathogen, has created an even distribution of maximum diversity from the smallest (leaf) to largest scales (>500 km), which will make breeding for resistance difficult. These data illustrate the evolutionary potential and danger of the introduction of multiple genotypes of a potentially outcrossing pathogen, especially when it has a high dispersal potential.     

Mitochondrial DNA diversity in an apomictic Daphnia complex from the Canadian High Arctic

Cyclic parthenogenesis is the ancestral mode of reproduction in the cladoceran crustacean, Daphnia pulex, but some populations have made the transition to obligate parthenogenesis and this is the only mode of reproduction known to occur in arctic populations. Melanism and polyploidy are also common in arctic populations of this species. Prior allozyme studies of arctic D. pulex revealed substantial levels of clonal diversity on a regional scale. Clonal groupings based on cluster analysis of allozyme genotypes do not conform to groupings based on the presence/absence of melanin or on ploidy level. In order to further elucidate genetic relationships among arctic D. pulex clones, mitochondrial DNA (mtDNA) variation was examined in 31 populations from two Canadian high-arctic sites. The data were also compared to a previous study of mtDNA variation in populations from a Canadian low-arctic site. Cladistic analysis of restriction site variation of the entire mitochondrial genome and nucleotide sequence variation of the mitochondrial control region was used to construct genetic relationships among mitochondrial genotypes. Three distinct mitochondrial lineages were detected. One lineage was associated with diploid, nonmelanic clones and is the same as the lineage that is found in temperate populations of D. pulex. The other two lineages (A & B) were associated with polyploid, melanic clones. Sequence divergence between the A and B lineages was 2.4%. Sequence divergence between D. pulex and either of these two lineages exceeded 3%. It is suggested that the melanic, polyploid clones are hybrids between males of D. pulex (and/or a closely related congener, D. pulicaria) and females of either of two ancestral melanic species that have mitochondrial lineages A and B. Geographic patterns of mitochondrial diversity in ‘melanic’ lineage B support the hypothesis of an high-arctic refuge for the ancestral species during the last glacial period.     

Evolutionary dynamics of mating system shifts in Arabidopsis lyrata

Outcrossing is the prevalent mode of reproduction in plants and animals despite its substantial costs, while selfing and mixed mating occur at much lower frequency. Comparative research on plants has demonstrated the lability of self‐incompatibility, but there is little information about the transition on a within‐species level from self‐incompatibility to predominant selfing. We studied variation in mating system among 18 populations of Arabidopsis lyrata within a phylogenetic context to shed light on the evolution of selfing. Realized and potential mating systems were assessed by genetic analysis with microsatellite markers and hand‐self‐pollinations on 30 plants from each population. The fraction of self‐incompatible plants in a population was highly correlated with the outcrossing rate, showing that the spread of self‐compatibility is accompanied by or soon followed by an increase in the rate of selfing. The four predominantly selfing populations (outcrossing rates < 0.25) fell into more than one phylogenetic cluster, suggesting that the transition to selfing occurred more than once independently. Hence, A. lyrata offers an opportunity for the comparative analysis of outcrossing as a predominant mode of reproduction in plants and of the causes of the shift to selfing.     

Intraspecific genetic structure,divergence and high rates of clonality in an amphi‐Atlantic starfish

Intraspecific genetic diversity and divergence have a large influence on the adaption and evolutionary potential of species. The widely distributed starfish, Coscinasterias tenuispina, combines sexual reproduction with asexual reproduction via fission. Here we analyse the phylogeography of this starfish to reveal historical and contemporary processes driving its intraspecific genetic divergence. We further consider whether asexual reproduction is the most important method of propagation throughout the distribution range of this species. Our study included 326 individuals from 16 populations, covering most of the species’ distribution range. A total of 12 nuclear microsatellite loci and sequences of the mitochondrial cytochrome c oxidase subunit I (COI) gene were analysed. COI and microsatellites were clustered in two isolated lineages: one found along the southwestern Atlantic and the other along the northeastern Atlantic and Mediterranean Sea. This suggests the existence of two different evolutionary units. Marine barriers along the European coast would be responsible for population clustering: the Almeria–Oran Front that limits the entrance of migrants from the Atlantic to the Mediterranean, and the Siculo‐Tunisian strait that divides the two Mediterranean basins. The presence of identical genotypes was detected in all populations, although two monoclonal populations were found in two sites where annual mean temperatures and minimum values were the lowest. Our results based on microsatellite loci showed that intrapopulation genetic diversity was significantly affected by clonality whereas it had lower effect for the global phylogeography of the species, although still some impact on populations’ genetic divergence could be observed between some populations.     

A contribution to characterisation of genetic variation in some natural Polish populations of Elymus repens (L.) Gould and Elymus hispidus (Opiz) Melderis (Poaceae) as revealed by RAPD markers*

To determine the relative importance of clonal growth and sexual reproduction, the Randomly Amplified Polymorphic DNA (RAPD) method was used to study genetic diversity and clonal structure of six populations of Elymus repens and four populations of Elymus hispidus from Poland. These outbreeding species are virtually self‐sterile and form widely spreading and long‐lived rhizomes. Using 12 primers, a total of 150 unambiguous RAPD fragments were amplified and scored. Results of AMOVA showed no significant genetic distinction between morphologically distinguished varieties of E. repens and E. hispidus. E. repens had slightly higher intra‐specific genetic polymorphism than E. hispidus; the percentage of polymorphic bands per population ranged from 38 to 49 and from 19 to 38 respectively. Clonal diversity measured using the Simpson diversity index (D) indicated different contributions of clonal reproduction in particular populations of E. repens (D: 0.20–0.72). Populations of E. hispidus were dominated by one or a few clones, which were generally restricted to a single population (D: 0.00–0.22). RAPD revealed that most genetic diversity resided within populations of the two studied species, suggesting that, despite their clonal character, propagation by seeds contributes considerably to reproduction of E. repens and E. hispidus.     

Genotypic variation in agamospermous Erigeron compositus (Asteraceae)

Few integrative analyses of the structure of agamospermous plant populations have been conducted. Erigeron compositus occurs in montane western North America and comprises both sexual and agamospermous populations. Sexual E. compositus has previously been characterized as outcrossing and predominantly diploid (2n = 18). Agamic E. compositus is usually hexaploid (2n = 54), though counts herein range from 2n = 36 to 2n = 80. Starch-gel electrophoresis, cytology, and analysis of pollen production were used to evaluate variation within and among agamospermous populations. Fifteen enzyme loci were used to identify 24 unique multilocus genotypes in seven populations, an average of 3.4 genotypes per population. Proportion of distinct genotypes per population sample size (GIN) and measures of genetic diversity (D) and evenness (E) are 0.10, 0.48, and 0.61, respectively, which indicate that E. compositus maintains levels of diversity similar to other agamospermous taxa. Most agamospermous populations are mosaics comprising groups of genetically distinct individuals that are frequently distinguished by cytotype and capacity for pollen production. The geographical and ecological separation of sexual and agamospermous populations make it unlikely that gene flow from sexual populations is a direct source of genetic variation in agamospermous populations. Instead, crossing between genetically distinct facultative agamosperms probably accounts for most variation. Genetic and morphological evidence document one such putative crossing event. Agamospermous E. compositus is very similar genetically to sexual E. compositus. Allozyme analysis further shows that genetic variation in agamospermous populations is partitioned among a few highly heterozygous genotypes, whereas sexual populations maintain numerous genotypes of relatively low heterozygosity.     

SPATIAL GENETIC STRUCTURE OF CLONAL AND SEXUAL REPRODUCTION IN POPULATIONS OF ADENOPHORA GRANDIFLORA (CAMPANULACEAE)

The spatial distribution of clonal versus sexual reproduction in plant populations should generally have differing effects on the levels of biparental inbreeding and the apparent selfing rate, produced via mating by proximity through limited pollen dispersal. We used allozyme loci, join-count statistics, and Moran's spatial autocorrelation statistics to separate the spatial genetic structure caused by clonal reproduction from that maintained in sexually reproduced individuals in two populations of Adenophora grandiflora, a perennial herb. Join-count statistics showed that there were statistically significant clustering of clonal genotypes within distances less than 4 m. Both the entire populations and the sets of sexually reproduced individuals exhibited significant spatial autocorrelation at less than about 12 m, and the sexually reproduced individuals are substantially structured in an isolation-by-distance manner, consistent with a neighborhood size of about 50.     

LONG-TERM EXPERIMENTAL EVOLUTION IN ESCHERICHIA COLI. III. VARIATION AMONG REPLICATE POPULATIONS IN CORRELATED RESPONSES TO NOVEL ENVIRONMENTS

Twelve populations of Escherichia coli were founded from a single clone and propagated for 2000 generations in identical glucose-limited environments. During this time, the mean fitnesses of the evolving populations relative to their common ancestor improved greatly, but their fitnesses relative to one another diverged only slightly. Although the populations showed similar fitness increases, they may have done so by different underlying adaptations, or they may have diverged in other respects by random genetic drift. Therefore, we examined the relative fitnesses of independently derived genotypes in two other sugars, maltose and lactose, to determine whether they were homogeneous or heterogeneous in these environments. The genetic variation among the derived lines in fitness on maltose and lactose was more than 100-times greater than their variation in fitness on glucose. Moreover, the glucose-adapted genotypes, on average, showed significant adaptation to lactose, but not to maltose. That pathways for use of maltose and glucose are virtually identical in E. coli, except for their distinct mechanisms of uptake, suggests that the derived genotypes have adapted primarily by improved glucose transport. From consideration of the number of generations of divergence, the mutation rate in E. coli, and the proportion of its genome required for growth on maltose (but not glucose), we hypothesize that pleiotropy involving the selected alleles, rather than random genetic drift of alleles at other loci, was the major cause of the variation among the derived genotypes in fitness on these other sugars.     

Population structure affected by excess gene flow in self-pollinating Elymus nutans and E. burchan-buddae (Triticeae: Poaceae)

Seed-mediated gene flow can considerably affect population genetic structure of strictly self-pollinating species, but little is known on the extent and nature of such gene flow among pastoral plant populations. Molecular fingerprints provide a powerful tool to address the relevant issues. Genetic structure of 22 populations of two self-pollinating pasture species, Elymus nutans and E. burchan-buddae, collected from various altitudes of the Qinghai–Tibetan Plateau was studied using fluorescence-based amplified fragment length polymorphism technique. Analysis of molecular variance revealed 42.97% and 37.63% among-population variation for the two Elymus species, respectively, indicating that the majority of the total variation presented within populations. This result contradicts the common genetic variation pattern for a selfing plant species: lower genetic variation within populations. Further analysis suggested higher level of gene flow among populations within the same region than among different regions across the sampled area for the two Elymus species. STRUCTURE analyses of the Elymus populations indicated an evident admixture genetic structure, particularly among neighboring populations from the same region, supporting the hypothesis of considerable seed dispersal among populations. The excess within-region gene flow of E. nutans and E. burchan-buddae might be caused by grazing animals that promote seed dispersal when moved around the pastoral lands during foraging. The among-population gene flow promulgated by grazing animals may promote the maintenance of genetic diversity in the pasture species, particularly in small and fragmented populations within a given region.     

ALLOZYME VARIATION WITHIN AND BETWEEN LASTHENIA MINOR AND ITS DERIVATIVE SPECIES,L. MARITIMA (ASTERACEAE)

Enzyme electrophoresis was employed to examine genetic variation at 20 loci in 16 populations of Lasthenia minor and 18 populations of its presumed derivative species L. maritima. The purposes of the study were to ascertain levels of genetic variation in each species, to assess how the variation at enzyme-coding genes is apportioned within and among populations of each species, and to determine the level of divergence between the two species. The two species are both diploid annuals, similar morphologically, and produce fertile F₁ hybrids when crossed. Lasthenia minor is self-incompatible and restricted to mainland California, whereas L. maritima is self-compatible and probably largely autogamous; it occurs on seabird rocks from central California to British Columbia. Mean genetic identities for pair-wise comparisons of populations of the two species are similar to values for populations of the same species, indicating they have not diverged at the 20 genes coding for soluble enzymes. Despite its more extensive geographical range, L. maritima exhibits only 50% of the genetic diversity of L. minor. The latter species apportions a greater amount of its diversity within populations, whereas the former harbors more diversity among populations than within them. This is probably a reflection of the different breeding systems of the two species. Six unique alleles were detected in L. minor, whereas only one novel allele was found in a single individual of L. maritima. The electrophoretic data are concordant with the suggestion that L. maritima is relatively recently derived from L. minor. The switch from outcrossing to selfing and selection of genotypes adapted to the chemically and physically unusual substrate on the seabird rocks are considered the critical steps in the evolution of L. maritima.     

Invasion history of North American Canada thistle,Cirsium arvense

Aim Canada thistle (Cirsium arvense– Cardueae, Asteraceae) is one of the worst invasive plants world‐wide. Native to Eurasia, its unintentional introduction into North America now threatens the native flora and is responsible for enormous agricultural losses. The goals of this study are to: (1) reconstruct the evolutionary history of C. arvense and estimate how often it may have colonized North America, (2) compare the genetic diversity between European and North American populations to detect signs of demographic bottlenecks and/or patterns of population admixture, and (3) conduct bioclimatic comparisons to infer eventual niche shifts following this species’ introduction into North America. Location Europe and North America. Methods A total of 1522 individuals from 58 populations were investigated with six microsatellite markers. Estimates of heterozygosity (H_E) and allelic richness (R_S) were quantified for each population, and population structure was inferred via analyses of molecular variance (AMOVAs), principal components analyses (PCAs), Mantel tests and Bayesian clustering analyses. Climatic niche spaces were based on 19 bioclimatic variables extracted from approximately 32,000 locations covering the entire range, and compared using PCA and hierarchical cluster analysis. Results Although there is evidence of multiple introductions from divergent European lineages, North American populations of C. arvense exhibited significantly lower levels of genetic diversity than their putative ancestors. Bioclimatic comparisons pointed to a high degree of niche conservatism during invasion, but indicated that genotypes from the former USSR and Central European mountain chains were probably best adapted to invade North America upon entry into the continent. Main conclusions Genetic and historical data suggest that C. arvense first entered North America from Western Europe with the first European settlers, and was later introduced from Eastern Europe into the prairie states during the agricultural boom. The species went through a significant bottleneck following its introduction into the New World, but the level of genetic diversity remained high owing to admixture between genetically differentiated lineages and to a highly efficient outcrossing breeding system.     

Rapid diversification of colouration among populations of a poison frog isolated on sky peninsulas in the central cordilleras of Peru

Aim Comparison of Epipedobates bassleri ( Myers, 1987 ), which occurs on high‐altitude mountain ridges (‘sky peninsulas’) in the Andean transition zone and demonstrates high levels of divergence in colouration among populations, and Epipedobates hahneli ( Schulte, 1999 ), which occurs throughout the lowland regions of the Amazon basin and is morphologically conserved, using phylogenetic analysis of mitochondrial sequence data and comparison of colour pattern. Location Central cordilleras of Peru (near Tarapoto, San Martin). Methods DNA was extracted from individuals of E. bassleri from the central cordilleras of Peru, and from individuals of E. hahneli from across Peru. The cytochrome b mitochondrial gene region was amplified and sequenced for individuals of each species, and phylogenetic analysis was carried out using Bayesian inference. Genetic distances among populations and geographic distances of each species were examined and compared using Mantel tests. Parametric bootstrapping was used to test the monophyly of E. bassleri. Results Epipedobates bassleri formed a well‐supported monophyletic group and showed higher levels of genetic divergence among populations than was shown among populations of E. hahneli from the same region. Distinct clades representing different geographic regions were recovered for E. hahneli. Levels of divergence among more geographically distant populations of E. hahneli were higher than levels of divergence among E. bassleri populations. We found a significant correlation between genetic divergence and geographic distance as measured along a 1000‐m contour line, but not as measured by direct routes (crossing putative biogeographical barriers). Main conclusions Levels of genetic divergence were higher among populations of morphologically conservative E. hahneli than among populations of morphologically variable E. bassleri, suggesting rapid divergence in colouration among populations of E. bassleri. These patterns support previous arguments concerning the role of the montane transition zone between the high mountains and lowlands in divergence and speciation. High levels of both genetic and phenotypic divergence among populations of E. bassleri indicate that ecological or behavioural factors may be responsible for the high levels of colour variation seen among E. bassleri, but not among E. hahnleli, populations.     

Genetic Structure and Gene Flow in Elymus glaucus (blue wildrye): Implications for Native Grassland Restoration

Interest in using native grass species for restoration is increasing, yet little is known about the ecology and genetics of native grass populations or the spatial scales over which seed can be transferred and successfully grown. The purpose of this study was to investigate the genetic structure within and among populations of Elymus glaucus in order to make some preliminary recommendations for the transfer and use of this species in revegetation and restoration projects. Twenty populations from California, Oregon, and Washington were analyzed for allozyme genotype at 20 loci, and patterns of variation within and among populations were determined. Allozyme variation at the species level was high, with 80% of the loci polymorphic and an average expected heterozygosity (an index of genetic diversity) of 0.194. All but two of the populations showed some level of polymorphism. A high degree of population differentiation was found, with 54.9% of the variation at allozyme loci partitioned among populations (F_st= 0.549). A lesser degree of genetic differentiation among closely spaced subpopulations within one of the populations was also demonstrated (F_st= 0.124). Self-pollination and the patchy natural distribution of the species both likely contribute to the low level of gene flow (N_m= 0.205) that was estimated. Zones developed for the transfer of seed of commercial conifer species may be inappropriate for transfer of E. glaucus germplasm because conifer species are characterized by high levels of gene flow. Limited gene flow in E. glaucus can facilitate the divergence of populations over relatively small spatial scales. This genetic differentiation can be due to random genetic drift, localized selective pressures, or both. In order to minimize the chances of planting poorly adapted germplasm, seed of E. glaucus may need to be collected in close proximity to the proposed restoration site.