摘要:

AbstractThe powdery mildew speciesErysiphe cichoracearumhas a described host range of over 300 plant species from among several families. Host‐range testing indicates host‐specialized subdivision within this taxonomic species. However, the extent of subdivision remains largely undetermined among host‐limited forms. We have characterized diversity among field collections ofE. cichoracearumfrom a variety of hosts, and from other powdery mildew species, with RFLPs from a PCR amplified ribosomal DNA (rDNA) segment TheE. cichoracearumsamples expressed six distinct RFLP haplotypes. Each haplotype was specific to either a single host or to a set of related host species. These haplotypes formed a continuum of divergence ranging from about 18–35% average pairwise distance from one another, while those from other mildew species clustered at consistently higher average pairwise distances fromE. cichoracearumand from each other. Our findings support earlier suggestions, based on host‐range and morphological characterizations, thatE. cichoracearumis a complex of morphologically similar, but host‐limited forms. Also, comparisons of rDNA haplotype distance betweenE. cichoracearumandBlumeria (Erysiphe) graminiswere consistently greater than betweenE. cichoracearumandSphaerotheca fulginea. This result supports earlier questions concerning the monophyletic nature

ISSN:0962-1083    

DOI:10.1111/j.1365-294X.1995.tb00221.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractRussia and western Asia harbour trout populations that have been classified as distinct species and subspecies, most often on the basis of morphological and ecological variation. In order to assess their origins and to verify whether traditional taxonomy reflects their evolutionary distinctiveness, we documented their genetic relationships on the basis of mitochondrial DNA (mtDNA) RFLP, mtDNA sequence analysis, and allozyme variation. Both mtDNA and nuclear gene variation defined two ancient phylogenetic assemblages of populations distributed among northern (Baltic, White, Barents), and southern (Black, Caspian, Aral) sea basins, between which gene flow has been possible but limited in postglacial times. These results supported the traditional taxonomic differentiation between populations of these two regions. They provided weak support for the taxonomic distinction of southern brown trout (Salmo trutta) populations based on their basin of origin. They also refuted the hypothesis that L. Sevan trout (Salmo ischchan) diverged from a primitive brown trout ancestor. Nevertheless, all trout populations from southern sea basins possessed private alleles or mtDNA genotypes and were genetically distinct Therefore, they represent unique gene pools that warrant individual recognition for conservation and management.

ISSN:0962-1083    

DOI:10.1111/j.1365-294X.1995.tb00222.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractThe genetic structure of field vole (Microtus agrestis) populations from northern Europe was examined by restriction fragment length polymorphisms of mitochondrial DNA (mtDNA) in 150 individuals from 67 localities. A total of 83 haplotypes was observed, most of which were rare and highly localized geographically. Overall nucleotide diversity was high (134%), but showed a tendency to decrease with higher latitude. Two major mtDNA lineages differing by 2% in nucleotide sequence were identified. A southern mtDNA lineage was observed in field voles from Britain, Denmark and southern and central Sweden, whereas voles from Finland and northern Sweden belonged to a northern lineage. The strict phylogeographic pattern suggests that the present population generic structure in field voles reflects glacial history: the two groups are derived from different glacial refugia, and recolonized Fennoscandia from two directions. A 150–200‐km‐wide secondary contact zone between the two mtDNA groups was found in northern Sweden. Distinct phylogeographic substructuring was observed within both major mtDNA g

ISSN:0962-1083    

DOI:10.1111/j.1365-294X.1995.tb00223.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractGenetic subdivision in local populations of the European house mice,Mus musculus domesticusandM. m. musculus, was analysed to study patterns of gene flow. The data consisted of frequencies of microsatellite alleles in 16 samples (250 individuals) from a total of 11 sites in Jutland, which included successive samples from three sites. Sequences of the control region of mitochondrial DNA in three successive samples from one site were also analysed. Microsatellite genotype frequencies within samples were close to Hardy‐Weinberg expectations. Levels of microsatellite differentiation among samples (θ= 0.05–0.21) corresponded to limited gene flow at migration‐drift equilibrium (Nm= 1–5). Weak isolation by distance for microsatellites inM. m. musculussuggested that gene flow tends to occur among neighbouring sites. Estimates of effective population size over a few generations were much lower than those corresponding to the long periods needed for arrival at mutation‐drift equilibrium. This suggested that subpopulations had been influenced by gene flow since formation, or had originated recently from genetically divers

ISSN:0962-1083    

DOI:10.1111/j.1365-294X.1995.tb00224.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractExtensive human impact in south western Australia has resulted in a high incidence of rarity throughout the highly endemic flora of the region.Grevillea scapigera(Proteaceae) is a typical example, with 27 plants (represented by four extant populations) remaining in the wild. In order to devise an appropriate strategy for the conservation of this species, its population genetics were studied using RAPD analysis, which enabled the discrimination of individual plants and the detection of a relatively high amount of variability (V = 0.32) withinG. scapigera.This variability was found to be evenly distributed within the plants analysed despite the clear distinction between most populations (87% of the variability being attributable to single plant difference and 13% to population difference). Finally, RAPD analysis was used to select a small group of plants that captured maximum genetic variability to be used in the recovery program of the species. Because of the low genetic difference between populations, the mixing of these selected plants during the recovery process should not create genetic imbalances. The methods used in this study provide a useful model for future projects involving the recovery of rare flora.

ISSN:0962-1083    

DOI:10.1111/j.1365-294X.1995.tb00225.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractWe postulated that the biogeographical history of South‐east Asia contributed to extensive admixture during Pleistocene low sea levels of genetic groups of an obligate freshwater fish (the river catfish,Hemibagrus nemurus) isolated during periods of high sea levels. During Pleistocene glacial maxima, the sea level was lower than at present and the islands of the Sunda shelf (Sumatra, Borneo and Java) and the Asian mainland were connected by lowlands traversed by rivers. Restriction fragment length polymorphisms in mitochondrial DNA were documented for 140 putativeH. nemurusanalysed from 13 sampling sites resulting in the definition of 35 haplotypes. The high level of haplotype differentiation (mean P × 100 = 2.22, SD = 1.33) indicates that the subdivision of the ancestralH. netnurusgroup was extensive and probably occurred early in the Pleistocene. The occurrence of some genetically divergent groups of theH. netnuruscomplex occurring in sympatry in widely separated locations supports the proposition that low sea levels aided the dispersion and mingling of genetic groups. Based on both genetic and morphological evidence, the mainH. nemurusline gave rise to three regional groups: (1) a morphologically distinct ‘Indochinese’ group composed of two mtDNA clades overlapping in east peninsular Malaysia; (2) a ‘Sundaic’ group composed of various lineages of differing morphology and genetic identity; (3) a genetically distinct ‘Sarawak’ group in west Borneo, similar in morphology to the ‘Sundaic’ and ‘Indochinese’ groups, but including a small, golden colour morph as a distinct dade. The morphologically similar Sundaic forms from west Java, Sumatra and west Borneo show some degree of genetic divergence, but their phylogenetic relationships are poorly resolved. The most genetically and morphologically distinct Sundaic dade, assigned toH. hoevenii, colonized the Kapuas river (west Borneo), east Sumatra and south peninsular Malaysia. Contrary to our original hypothesis and present biogeographical theory, little exchange of genetic groups has apparently occurred between the mainland and the Sunda Islands dur

ISSN:0962-1083    

DOI:10.1111/j.1365-294X.1995.tb00226.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractAttempts to study the genetic population structure of large mammals are often hampered by the low levels of genetic variation observed in these species. Polar bears have particularly low levels of genetic variation with the result that their genetic population structure has been intractable. We describe the use of eight hypervariable microsatellite loci to study the genetic relationships between four Canadian polar bear populations: the northern Beaufort Sea, southern Beaufort Sea, western Hudson Bay, and Davis Strait ‐ Labrador Sea. These markers detected considerable genetic variation, with average heterozygosity near 60% within each population. Interpopulation differences in allele frequency distribution were significant between all pairs of populations, including two adjacent populations in the Beaufort Sea. Measures of genetic distance reflect the geographic distribution of populations, but also suggest patterns of gene flow which are not obvious from geography and may reflect movement patterns of these animals. Distribution of variation is sufficiently different between the Beaufort Sea populations and the two more eastern ones that the region of origin for a given sample can be predicted based on its expected genotype frequency using an assignment test. These data indicate that gene flow between local populations is restricted despite the long‐distance seasonal movements undertaken by polar be

ISSN:0962-1083    

DOI:10.1111/j.1365-294X.1995.tb00227.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractSpartina altemiflora(smooth cordgrass) has invaded Willapa Bay, Washington, covering bare mud flats and seagrass beds. At current expansion rates it threatens to occupy most of the intertidal habitat in the bay within 40 years. Although a major mitigation effort is underway, nothing is known about the genetic structure of the Willapa BayS. altemiflorapopulation or the underlying causes for the dramatic increase in seed set that has occurred in the last 15 years. Random amplified polymorphic DNA (RAPD) analysis was assessed as a method of DNA fingerprinting to analyse the genetic history and current structure of the Willapa population. The results suggest that allS. alternifloraclones in Willapa Bay are descended from a single genet. Given the limited genetic variability expected in a clonally founded population, we discuss the utility of RAPDs as genetic markers to explore the large morphological and reproductive differences reported among Willapa clones. Cluster analysis of RAPD fragments was used to show relatedness amongS. altenifloragenets and may be helpful in locating the most prolific clones for mitigation efforts. Overall, RAPDs show great potential in genetic analysis ofS. altemiflora, particularly in invasive populations where isozyme variability is low or nonexistent.

ISSN:0962-1083    

DOI:10.1111/j.1365-294X.1995.tb00228.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractA total of nearly 800 base pairs of mitochondrial DNA sequence was assayed in each of 52 musk turtles (Sternotherus minor) collected across the species' range in the south‐eastern USA. About one‐half of the sequence information in effect was accessed by conventional recognition‐site assays of the entire mtDNA molecule; the remainder came from direct sequence assays of a normally hypervariable 5′ section of the noncoding control region. The two assay methods produced essentially nonoverlapping sets of variable character states that were compared with respect to magnitudes and phylogeographic patterns of mtDNA variation. The two assay procedures yielded nearly identical outcomes with regard to: (a) total levels of species‐wide mtDNA genetic variation; (b) mean levels of within‐locale variation; (c) extremely high population genetic structure; (d) a phylogenetcally significant separation of samples from the north‐western half of the species' range vs. those in the south‐eastern segment; and (e) considerably lower genetic variability within the north‐western clade. The micro‐ and macro‐phylogeographic mtDNA patterns in the musk turtle are consistent with a low‐dispersal natural history, and with a suspected longer‐term biogeographic history of

ISSN:0962-1083    

DOI:10.1111/j.1365-294X.1995.tb00229.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractSamples of the grain aphidSitobion avenue(F.) and the rose‐grain aphidMetopolophium dirhodum(Walker) were collected in late March from wheat fields and adjacent road‐side grasses at a number of locations in southern England. Unparasitized aphids were DNA fingerprinted using the multilocus (GATA)4probe. Over all locations, the fingerprints of individualS. avenuecaught in wheat had lower overall average distances of band migration (ADBM) and shared a higher proportion of bands, than fingerprints of individuals caught in adjacent road‐side grasses. The ADBM of fingerprints ofS. avenuecollected on road‐side grasses altered significantly with geographical location, while the ADBM of fingerprints ofS. avenuecaught on wheat did not. A comparison of the fingerprints of individualM. dirhodumcaught in wheat and neighbouring road‐side grasses did not reveal any genetic differentiation. Fingerprints ofM. dirhodumthat were caught in the same host type did however, show significant variation in ADBM between different locations. With bothS. avenueandM. dirhodum, spatial autocorrelation revealed that locations that were close together were no more likely to have individuals with similar ADBM than locations mat were far apart Our results suggest that (i) particular clones of S. avenue prefer to colonize wheat; and/or that (ii) particular clones ofS. avenaeperform better on wheat man other clones. It is unclear whyM. dirhodumdid not show any genetic structuring according to host type, but this species appears to engage in sexual reproduction much more frequently thanS. avenaein southern England.M. dirhodumis likely to have displayed genetic heterogeneity between locations either because of founder effects, or because of gene

ISSN:0962-1083    

DOI:10.1111/j.1365-294X.1995.tb00230.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY