摘要:

AbstractGenetically engineered microbes (GEMs) have the potential to revolutionize agricultural techniques by facilitating crop protection and increased productivity. However, there has been widespread concern regarding the potential impact these microbes may have on the environment. Here we mathematically model the dynamics of GEMs in an agricultural setting, focusing on parameters that can be used to summarize the potential of modified microbes for persistence and spread. First developing a comprehensive model for the dynamics of GEMs which includes mobile and stationary classes of GEMs as well as competition from indigenous microflora, we then analyse a sequence of simplified mathematical models with a view to answering two fundamental questions: (1) will the GEMs spread (or invade), and if so how quickly? and (2) what are the best strategies for containing the spread of GEMs in a spatially varying environment?

ISSN:0962-1083    

DOI:10.1046/j.1365-294X.1996.00228.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractLittle is known about the population processes that shape the genetic diversity in natural populations of rhizobia. A sample of 912Rhizobium leguminosarumbiovartrifoliiisolates were collected from naturalized red clover populations (Trifolium pratense) and analysed for 15 allozyme loci to determine the levels and distribution of genetic diversity. Hierarchical analyses compared different sampling levels, geographical separation, and temporal separation. Total genetic diversity across all isolates wasH= 0.426, with 57.6% of the total diversity found among isolates obtained from individual red clover plants. Relatively low genetic differentiation among populations and high differentiation among plants within populations was observed; this suggests that gene flow and founder effect act differently at geographical and local scales. Significant differences were observed in (i) allele frequencies among populations and among plants within populations, and (ii) the frequency distribution of the most widespread and the most abundant strains. When multilocus linkage disequilibrium was calculated, significant levels of disequilibrium were observed in the total sample and in three of the eight populations.

ISSN:0962-1083    

DOI:10.1046/j.1365-294X.1996.00257.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractRestriction fragment length polymorphism analysis of mitochondrial DNA (mtDNA) was used to reconstruct postglacial dispersal routes of arctic charrSalvelinus alpinusin North America. Twelve of 35 restriction enzymes detected polymorphisms among representative populations, revealing two distinct lineages with an estimated nucleotide divergence of 1.32%. Subsequent screening of 869 fish from 54 populations with four diagnostic restriction enzymes showed that these lineages have largely allopatric distributions, suggesting their dispersal from separate northern and eastern glacial refugia. In addition, geographical and genetic structure among eastern populations suggested the existence of a second eastern refuge. Among the three lineages, the most divergent (Arctic) lineage occurred from Alaska east to northern Labrador. Quebec, New Brunswick, and New England were colonized by a second (Laurentian) lineage, and Labrador by a third group. Contact between refugial groups was only detected in two Labrador populations. The Arctic lineage was highly differentiated from eastern North American and European haplotypes, and probably diverged during the early Pleistocene. By contrast, the Laurentian and Labrador groups were similar to Old World charr, suggesting a shared ancestry during the mid‐Pleistocene. In addition, the close relationship between Labrador and Laurentian charr indicates their probable divergence during the Wisconsinan glaciatio

ISSN:0962-1083    

DOI:10.1046/j.1365-294X.1996.00265.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractBeets are a crop of particular concern regarding invasiveness questions because they commonly become feral due to unintentional hybridization with annual forms of wild beets. In this study the performance of transgenic beets resistant to Beet Necrotic Yellow Vein Virus (BNYVV) was compared to the performance of unmodified material from the same breeding line. Both transgenic and control genotypes were also compared to a conventionally bred variety carrying a similar phenotypic trait. Field tests were developed in a step by step fashion in order to study seed emergence and competitiveness in early life stages. The tests quantified the potential ecological advantage of virus resistance under virus and non‐virus infestation conditions. In experimental field releases in 1993 and 1994 in Germany, a small but increasingly clear ‘additive’ ecological advantage of the genetically engineered trait was detected. In both years and all competition treatments, the conventional tolerant variety performed best. An impact of naturalization on natural, non‐agricultural habitats may appear in wild beet populations in Italian seed beet production areas. However, a survey of coastal areas of North‐Eastern Italy found no virus infestation in 1994, suggesting that an increase in wild beet fitness is unlikely

ISSN:0962-1083    

DOI:10.1046/j.1365-294X.1996.00075.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractGenetic variation at 47 protein loci was investigated in 16 wild brown trout populations from the Po basin and three major domesticated stocks used for stocking this area. Twenty‐four loci were polymorphic and large frequency differences were found at 15 of them. The most significant allozyme variations were congruent with the mtDNA sequence polymorphism previously observed in the same samples. We confirmed the occurrence of two parapatric incipient species,Salmo marmoratusandS. trutta fario, previously identified by morphological traits. These two species were fixed or nearly fixed for alternate alleles at eight loci (Nei's standard genetic distance = 0.16–0.18), but introgression was detected between adjacent samples of the two forms. Divergence levels at both mtDNA and nuclear loci suggested that the differentiation betweenS. marmoratusandS. trutta fariostarted between 3 and 1 million years before present. Variation at protein loci and mtDNA supported the hypothesis that the third species found in this area,S. carpio(an endemic population of the lake Garda) was issued from a recent hybridization of the two first species. Finally, we showed that three of the major Italian fish‐farm strains originated from the Atlantic side and displayed substantial genetic differences with the natural populations of the Po basin. Most of these populations were contaminated by stocking with introgression rate ranging from 0 to 70% and measures of protection and restoration of the rich genetic diversity present in this area should be urgently ap

ISSN:0962-1083    

DOI:10.1046/j.1365-294X.1996.00074.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractMultilocus DNA fingerprinting is commonly used to assess genetic similarity within and between geographically disjunct populations. Typically, the proportion of DNA fingerprinting bands shared between two individuals (SXY) is calculated for all possible pair‐wise comparisons and the resulting data analysed parametrically to test differences in mean band‐sharing among groups. The degree to which covariation among interdependent SXYvalues (Sab‐ Sbc) biases the analyses is often unknown. Here, we assess the extent of covariation in four DNA fingerprinting studies and evaluate the effectiveness of two corrective procedures, a permutation test and a subsampling routine using only independent pairwise comparisons drawn without replacement from the overall data. Covariation among interdependent SXYvalues was significantly greater than zero in every data set examined, including those from a bee, a rodent, and two passerine birds. Permutation tests did not correct for interdependence and yielded significance values nearly identical to those derived from uncorrected parametric procedures. In contrast, the subsampling procedure yielded corrected estimates of the standard error that were two to four times larger than those derived parametrically. As a result, comparisons that were significant using parametric tests were either non‐significant or only marginally significant with the subsampling routine. We conclude that interdependence among SXYvalues poses a substantial obstacle to hypothesis testing that must be addressed in future

ISSN:0962-1083    

DOI:10.1046/j.1365-294X.1996.00080.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractThe population genetic structure of three species of Amazonian rodents (Oligoryzomys microtis, Oryzomys capito, andMesomys hispidus) is examined for mtDNA sequence haplotypes of the cytochrome b gene by hierarchical analysis of variance and gene flow estimates based on fixation indices (NST) and coalescence methods. Species samples are from the same localities along 1000 km of the Rio Jurua in western Amazonian Brazil, but each species differs in important life history traits such as population size and reproductive rate. Average haplotype differentiation, hierarchical haplotype apportionment, and gene flow estimates are contrasted in discussing the current and past population structure. Two species exhibit isolation by distance patterns wherein gene flow is largely limited to geographically adjacent localities.Mesomysexhibits this pattern throughout its range along the river. More than 75% of haplotype variation is apportioned among localities and regions, and estimates ofNmfor pair‐wise comparisons are nearly always less than 1.Oligoryzomysshows weak isolation by distance, but only over the largest geographical distances.Nmvalues for this species are nearly always above 1 and most (about 80%) of haplotype variation is contained within local populations. In contrast,Oryzomysexhibits no genetic structure throughout its entire distribution;Nmvalues average 17 and nearly 90% of the total haplotype variance is contained within local populations. Although gene flow estimates are high, the pattern ofNmas a function of geographical distance suggests that this species experienced a more recent invasion of the region and is still in genetic disequilibrium under its current demographic condition

ISSN:0962-1083    

DOI:10.1046/j.1365-294X.1996.00077.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractDistinguishing between primary and secondary intergradation among differentiated populations, and the relative importance of drift and selection, are persistent problems in evolutionary biology. An historical perspective on population interactions can provide insight into the nature of contacts, and thus help resolve these questions. Continuously distributed populations ofAnolis marmoratusfrom the island of Basse Terre in the Guadeloupean archipelago of the Lesser Antilles show a striking degree of geographic variation in morphology. Initial surveys of mtDNA variation from throughout the Guadeloupean Archipelago revealed one case where levels of sequence difference and phylogenetic relationships of alleles from morphologically differentiated populations from the east coast of Basse Terre were consistent with primary intergradation. In this paper, I examine the genetic population structure of a series of populations spanning this north‐south cline in morphological variation to test the hypothesis of primary intergradation. Sequences of the mitochondrial cytochrome‐b gene from 50 individuals representing five populations spanning the cline were obtained and fourteen unique haplotypes (differing by 2% or less) were detected. Patterns of nucleotide substitution among haplotypes do not deviate from neutral expectation indicating no effect of selection at the level of mtDNA sequences. Estimates of population structure and gene flow were made using both summary statistics for nucleotide diversity (Nat) and cladistic methods. The results are sensitive to the choice of gene flow model, and this is discussed in detail. Mitochondrial variation in the northern populations may not be at equilibrium, and the phylogeny of alleles is consistent with a recent increase in effective population size. Estimates of nucleotide diversity, gene flow, and the phylogenetic relationships of haplotypes indicate that the southern‐most population (representing the extreme of morphological variation along this cline) has been relatively isolated from populations to the north and has experienced a reduced effective population size. The apparent clinal variation between the southern population and the others may therefore reflect secondary contact and introgression rather than primary intergrad

ISSN:0962-1083    

DOI:10.1046/j.1365-294X.1996.00082.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractThe vast majority of perennial plants reproduce sexually and vegetatively at the same time. This may lead to important variation among clonal plant populations in their amount of genotypic diversity. In order to verify this assumption, we compare the clonal diversity of 10 natural populations of the aquatic clonal macrophyteSparganium erectumin France. Diversity was quantified by DNA fingerprinting and allozyme electrophoresis for a sample of 10 shoots per population. Two DNA probes (CA)3and (TAA)6TA, were selected among 10 synthetic oligonucleotide probes containing simple repeat motifs. Both allozymes and DNA fingerprints revealed different amounts of diversity among populations. Five populations consist of a single genotype, whereas two populations were genetically highly diverse. In four of the monomorphic populations, absence of fingerprints diversity was combined with uniformly heterozygous allozyme loci, suggesting that each population was composed of a single clone. In the highly diverse populations, the level of clonal diversity combined with the allele segregation of the two allozyme lociLapandEstsuggests frequent seedling recruitment. The origin of new genotypes remains unclear but the absence of widespread genotypes together with the discrete distribution ofSparganium erectumpopulations implies that new genotypes are locally produced through sexual reproduction.

ISSN:0962-1083    

DOI:10.1046/j.1365-294X.1996.00085.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractThe population genetic structure of the butterflyMelitaea didymawas studied along the northern distribution range border in Central Germany by means of allozyme electrophoresis. Individuals were sampled from a total of 21 habitat patches from four regions, and two provinces. Sampling was designed to estimate local vs. regional differentiation. High levels of variability were found,He= 0.14‐0.21. The mean expected sample heterozygosity from one region, Mosel, was significantly lower than from the Hammelburg region,He= 0.17 and 0.19, respectively. Two hierarchical levels of genetic differentiation were found. Within regions individuals sampled from different patches behaved as belonging to one population with high levels of gene flow (HammelburgFST= 0.015, MoselFST= 0.044), though local isolation barriers did create a substructuring of these populations. The inbreeding coefficients,FIS, were constant over all sample levels, suggesting a similar distribution of habitat patches within regions. Between regions gene flow was limited. An isolation by distance analysis indicated that the hierarchical structure, at the provincial level, may be breaking down due to isolation of regional populations. A more general observation was that the sampling design may greatly have influenced the estimation of genetic differentiation. Depending on which samples were included, overallFSTestimates ranged from 0.059‐0.

ISSN:0962-1083    

DOI:10.1046/j.1365-294X.1996.00088.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY