Low impact of present and historical landscape configuration on the genetics of fragmented Anthyllis vulneraria populations

Decreasing habitat fragment area and increasing isolation may cause loss of plant population genetic diversity and increased genetic differentiation between populations. We studied the relation between the historical and the present landscape configuration (i.e., patch area and patch connectivity), and the present management of calcareous grassland fragments on the one hand, and the within and between population genetic structure of 18 Anthyllis vulneraria populations on the other hand. Despite the long-time fragmentation history and the mainly selfing breeding system of the species, we detected very low genetic differentiation (Φ_st = 0.056) among habitat fragments and no significant isolation-by-distance relation. Average within fragment genetic diversity measured as molecular variance and expected heterozygosity, were relatively high (16.46 and 0.28, respectively), and weakly positively correlated with the current fragment area, most likely because larger fragments contained larger populations. We found no effects of the historical landscape configuration on the genetic diversity of the populations. Our data suggest that the consequences of habitat fragmentation for genetic differentiation and genetic diversity of A. vulneraria are relatively minor which is very likely due to the historical high levels of seed exchange among fragments through grazing and roaming livestock. This study provides indirect evidence that nature management by grazing not only positively affects habitat quality but that it might also mitigate the genetic consequences of habitat fragmentation. From the conservation point of view, this study illustrates the importance of grazing and of the regular transport of livestock between fragments to prevent the long-term effects of fragmentation on the genetic diversity of the populations studied.     

Genetic differentiation among populations of a specialist fishing bat suggests lack of suitable habitat connectivity

Specialist species face higher extinction risks as a result of smaller, isolated populations with reduced gene flow. The large-footed myotis (Myotis macropus) is the only microbat in Australia specialised for foraging directly over water surfaces. Such highly specialised feeding ecology restricts the distribution of M. macropus to coastal regions and inland waterways. Using five novel and two existing nuclear microsatellite markers, we investigated genetic diversity within and among five M. macropus populations in Victoria. Significant genetic differentiation was detected between all populations. F_ST values between populations ranged from 0.02 to 0.24. We suggest that the movement of M. macropus throughout the landscape is constrained by the availability of permanent waterways and associated riparian habitats. These findings represent important considerations for the conservation of this specialist species and the management of riparian vegetation, particularly on private land.     

Genetic diversity in wild Tunisian populations of Mentha pulegium L. (Lamiaceae)

The allozyme variation of 15 Tunisian wild populations of Mentha pulegium L. threatened by human activities (clearing, hard-grazing, ploughing, traditional uses) was surveyed by the analysis of 14 isozyme loci using horizontal gel starch electrophoresis. The species exhibited a high level of genetic variation within populations (the mean Ap = 2.20, P = 72%, Ho = 0.349 and He = 0.229), which indicates a predominately outcrossing mating system and the recruitment of new genotypes via dispersal seeds. The genetic structure analysis of the populations using F statistics indicates no inbreeding, and showed an excess of heterozygosity for few loci. The moderate differentiation of populations (F_ST = 0.110) and the low rate of gene flow between them (Nm = 2.02) might been caused by recent isolation of the populations through biotope disturbances. The value of Nei's genetic identity varied from 0.839 to 0.999 reflecting a relatively low genetic divergence between populations. Cluster analysis using UPGMA method and Nei's genetic identity values, showed that populations geographically close didn't always cluster together. However, populations within the same bioclimatic stage generally subclustered together indicating that differentiation between bioclimatic regions occurred.     

雄配子体选择的遗传分化效应及其在植物改良中的应用

在植物世代交替的生活史中,配子体是产生配子和具有单倍数染色体的植物体,并且有自己的遗传表达信息。在配子产生的过程中以及配子结合之前,适者生存的法则对配子发挥着选择作用,只有最适应外界环境条件的配子才能通过竞争性受精并产生合子。雄配子体选择是影响植物遗传分化、演变和遗传多样性的重要因素,被认为是生物进化的有力动力。此外,由于植物基因组中约有2/3的基因表达交错发生在配子体阶段和孢子体阶段,因此雄配子体选择的结果会影响到下一代孢子体的表现型。在育种实践中,利用雄配子体选择对植物进行遗传改良,具有提高选择机率和缩短育种年限等优点。本文主要概述雄配子体选择与孢子体表型的关系、遗传分化效应及其在植物遗传改良中的应用,以期为雄配子选择相关研究提供参考     

Impact of landspread sewage sludge and earthworm introduction on established earthworms and soil structure

Summary Sewage sludge was applied to twelve 4-m² plots in two forest (mixed hardwood, Norway spruce plantation) site and one old field site. The earthworm Eisenia fetida was introduced to half the control and half the treated plots. Earthworm populations were sampled by formalin extraction and hand-sorting five times in the year following treatment. One year after treatment, soil samples were wet-sieved and water-stable aggregate size-class arrays were determined.The dominant earthworm in the study site, Lumbricus terrestris, increased in density and mean individual biomass in response to sludge treatment in mixed hardwood and old field plots. In the Norway spruce plots, L. terrestris increased in individual biomass but decreased in density following sludge application. The density of the introduced E. fetida rapidly declined in all control plots. One year after introduction, E. fetida was found only in the sludge-treated Norway spruce plot. The introduction of E. fetida with sludge decreased the density and biomass of L. terrestris in the hardwood plots.Sludge treatment increased the percentages of 4-mm diameter water-stable aggregates in old field and hardwood plots. The addition of E. fetida with sludge in the hardwood plots generated no increase in 4-mm water-stable aggregates. In the old field, sludge + E. fetida increased the 4-mm water-stable aggregates. Little change in water-stable aggregates in response to either treatment combination was seen in the Norway spruce site.     

Spontaneous gene flow and population structure in wild and cultivated chicory, Cichorium intybus L.

Spontaneous gene flow between wild and cultivated chicory, Cichorium intybus L., may have implications for the genetic structure and evolution of populations and varieties. One aspect of this crop-wild gene flow is the dispersal of transgenes from genetically modified varieties, e.g. gene flow from GM chicory to natural chicory could have unwanted consequences. With the purpose to identify and quantify crop-wild gene flow in chicory, we analysed introgression in 19 wild chicory populations and 16 accessions of chicory varieties and landraces distributed across Northern, Central and Mediterranean Europe. The analysis used 281 AFLP markers and 75 SSAP markers giving a total of 356 polymorphic markers. Results from model based assignments with the program STRUCTURE indicated many incidents of recent gene flow. Gene flow was observed both between cultivars and wild populations, between landraces and wild populations, between different wild populations as well as between cultivars. Population structure visualized by distance-based clustering showed a North–South geographical structuring of the wild populations, and a general grouping of the cultivars corresponding to known origin. The results indicated, however, that the structuring between the two groups of wild and cultivated types was weak. As crop and wild recipients are genetically close and genes are transferred between the two types rather frequently, focus on mitigating crop-wild gene flow should be increased, before transgenic varieties are cultivated openly.     

Effects of earthworms on decomposition and metal availability in contaminated soil: Microcosm studies of populations with different exposure histories

Population-specific differences in the responses of earthworms to simultaneous exposure to Cu and Zn were studied in microcosm experiments. Two populations of Aporrectodea caliginosa tuberculata (Eisen) with different metal exposure histories were chosen for the studies. Microcosms were prepared containing either uncontaminated soil or soils with low or high combined Cu/Zn -concentrations (79/139 or 178/311 mg kg⁻¹ dry mass of soil, respectively). Earthworms from each population were introduced to the microcosm treatments with some microcosms serving as controls without earthworms. One series of microcosms was destructively sampled after 16 weeks incubation in a climate chamber. Survival, growth, reproduction and decomposition by earthworms in each treatment were measured. An additional microcosm series was sampled for soil and earthworm measurements at four weeks intervals to determine temporal changes in the availability of metals in the soils and their accumulation into earthworms. Cu and Zn were sequentially extracted from the soil samples of both microcosm series to estimate mobility and availability of the metals in the soil. Earthworms with long-term exposure history to metal-contaminated soil seemed to tolerate higher soil metal concentrations than earthworms without earlier exposure. Both earthworms and metals affected soil respiration (CO₂ production) and nitrogen mineralization. In addition, earthworms seemed to decrease the mobility and bioavailability of metals in the soil through their burrowing activity.     

Genetic diversity and local population structure of fragmented populations of Trillium camschatcense (Trilliaceae)

Trillium camschatcense, a long-lived common woodland herb, has been experiencing intensive habitat fragmentation over the last century in eastern Hokkaido, Japan. We examined the genetic diversity and population genetic structure of 12 fragmented populations with different population sizes using allozyme electrophoresis. The percentage of polymorphic loci and mean number of alleles per locus were positively related to population size, probably due to the stochastic loss of rare alleles (frequency of q<0.1) in small populations. Populations with 350 flowering plants or fewer had lost almost all of their rare alleles. While the heterozygosity and inbreeding coefficient were not related to population size, some small populations showed relatively high inbreeding coefficients. In spite of the low genetic differentiation among overall populations (F_ST=0.130), local population structuring was recognized between the two geographically discontinuous population groups. Within groups, sufficient historical gene flow was inferred, whereas a low dispersal ability of this species and geographical separation could produce apparent differentiation between groups.     

Genetic and morphological divergence in island and mainland birds: Informing conservation priorities

Evolutionary processes can complicate conservation efforts for species with uncertain taxonomic classifications and discrete geographic populations. Discordant morphological and genetic patterns across the geographic range of species further calls for the identification of evolutionary significant units for conservation. Using island and mainland populations of a small Australian passerine (the superb fairy-wren, Malurus cyaneus), we examine the relationship between morphological and genetic divergence among two subspecies, M. c. ashbyi (Kangaroo Island, South Australia) and M. c. leggei (South Australia, mainland), using eight microsatellite markers. Island birds showed clear evidence for morphological divergence, with a larger body size and thinner bill compared to mainland birds. Two genetic clusters were found using Bayesian methods, comprising mainland and island regions. Estimates of recent migration rates between all sites were very low (<2%). Morphological and genetic differentiation between island and mainland sites correlated significantly, but not when controlling for isolation by distance. Genetic and morphological substructure was evident with three distinct genetic clusters in each region. Males, the highly sedentary sex, appeared to drive correlations between morphological and genetic differentiation. Our study provides evidence that the subspecies classification of M. cyaneus in island and mainland regions encapsulates two independently diverging populations that can be recognised in conservation planning.     

Assessment of genetic diversity and genetic relationships among 29 populations of <Emphasis Type="Italic">Azadirachta indica</Emphasis> A. Juss. using RAPD markers

Randomly amplified polymorphic DNA (RAPD) analysis was employed to assess genetic divergence among 29 neem accessions collected from two agro-ecological regions of India (11 agro-climatic sub-zones), which cover three states, Punjab, Haryana and Rajasthan. Out of 24, 10-mer random primers used for studying genetic divergence, 14 were polymorphic, generating a total of 73 amplification products with an average of 5.21 products per polymorphic primer and estimated gene diversity of 0.49. Genetic relationships among accessions were evaluated by generating a similarity matrix based on Jaccard’s coefficient, ranging from 0.70 to 0.96. The phenetic dendrogram generated by UPGMA analysis grouped accessions into five clusters. RAPD performed within accessions (individual seedlings collected from the same mother plant) showed no variation indicating homogeneous population within accessions. Primers OPA-18, OPC-08 and OPI-03 were found most informative based on their resolving power. The degree of genetic variation detected among the 29 accessions with RAPD analysis suggests that RAPD can be used for studying genetic diversity in neem. The study also demonstrated that neem germplasm collected from northwestern plains of India shows no eco-geographical isolation based on sub-zones because accessions collected from different sub-regions are grouping together in the genetic tree.     

Invasion of a deciduous forest by earthworms: Changes in soil chemistry, microflora, microarthropods and vegetation

Ecosystems of northern North America existed without earthworm fauna until European settlers arrived and introduced European species. The current extent of invasion by some of these species, Lumbricus terrestris L., Octolasion tyrtaeum Savigny and Dendrobaena octaedra Savigny, into an aspen forest in the Canadian Rocky Mountains and the effects of the invasion on soil chemistry, microflora, soil microarthropods and vegetation were investigated. Densities of earthworm species, soil structure, plant coverage and abundance were determined along three transects starting at the edge of the forest. At locations with L. terrestris, litter was incorporated into the soil, and where O. tyrtaeum was present, organic layers were mixed with mineral soil layers. Organic layers disappeared almost entirely when both species occurred together. Carbon and nitrogen concentrations were reduced in organic layers in the presence of L. terrestris and O. tyrtaeum. Microbial biomass and basal respiration were reduced when L. terrestris and O. tyrtaeum were present, presumably due to resource competition and habitat destruction. Microarthropod densities and the number of microarthropod species were strongly reduced in the presence of O. tyrtaeum (−75% and −22%, respectively), probably through mechanical disturbances, increasing compactness of the soil and resource competition. The coverage of some plant species was correlated with earthworm abundance, but the coverage of others was not. Despite harsh climatic conditions, the invasion of boreal forest ecosystems by mineral soil dwelling earthworm species is proceeding and strongly impacts soil structure, soil chemistry, microorganisms, soil microarthropods and vegetation.     

Influence of habitat fragmentation on the genetic structure of Polyommatus coridon (Lepidoptera: Lycaenidae): implications for conservation

Conservation biologists pay increasing attention to the interdependence between habitat structure and genetic patterns of species and to the importance of conserving genetic diversity. A suitable model species for such a study is Polyommatus coridon, a butterfly of dry calcareous grassland. We studied the population genetic structure of 22 western German populations of this species (874 individuals). We observed no congruence between the observed genetic structure and the geographic arrangement of the studied populations. Genetic diversity was slightly higher in large populations than in small populations. Differentiation among populations was weak or even missing. Populations of an area with high habitat density showed no significant differentiation, whereas areas with low habitat densities showed significant genetic differentiation among populations. At present, hierarchical variance analysis revealed no differentiation between four distinguished limestone areas. The combination of all analytical results allow the definition of management units for P. coridon. Conservation measures are proposed from which a large number of rarer species occurring together with P. coridon will benefit.     

Genetic diversity and relationships among cultivated and wild accessions of tartary buckwheat (Fagopyrum tataricum Gaertn.) as revealed by RAPD markers

The methodology of sampling and the selection of a proper marker systemfor the analysis of accessions are major concerns in the evaluation of gene bank material. In our study the RAPD analysis of bulked DNA samples and single seedsDNA was successfully employed to evaluate intra- and inter-population geneticvariability of cultivated and wild tartary buckwheat accessions. The bulkingapproach enabled the distinction of all 40 analysed accessions and theirseparation into geographically well defined clusters. Three wild populations,two from Sichuan and one from Qinghai, formed a group that was geneticallyrelatively distant from wild populations from Tibet and all cultivatedlandraces which, on the other hand, exhibited very close relationships. Thesingle seed study that was used after bulked DNA analysis provided detailedinformation of the genetic variation present within some accessions of specialinterest. A moderate level of genetic variability was detected betweenaccessions and the variability was partitioned into between- andwithin-population components. On average, most of the detected variation ispresent between F. tataricumpopulations. The genetic and geographic distribution of variability is furtherdiscussed. We demonstrated the usefulness of combining bulking and single seedstudy approaches for the effective evaluation of genetic variability inF. tataricum accessions that couldalso have wider applicability in the management of plant genetic resources andphylogenetic studies.     

Genetic differentiation in the olive complex (Olea europaea) revealed by RAPDs and RFLPs in the rRNA genes

We assessed the genetic differentiation of the Mediterranean olive from its wild relatives found in different geographic areas (Mediterranean, Asia, Africa) using eighty RAPDs revealed with eight primers. Variance analysis (AMOVA) enabled us to estimate the overall genetic differentiation parameters between wild populations. Oleasters from the Near East and Turkey were discriminated from the other Mediterranean populations. Olea laperrinei, O. maroccana and O. cerasiformis were the taxa the most related to the Mediterranean olive. In contrast, O. africana was shown to be the most genetically distant taxa from the Mediterranean olive. However, we characterised hybrid trees between these two taxa. Significant trends between genetic and geographic distances were met within the subspecies cuspidata and within the Mediterranean olive. A genetic diversity gradient was observed in both subspecies europaea and cuspidata. These results are in agreement with a mechanism of differentiation by distance in the O. europaea complex, but another non-exclusive mechanism could also be gene flow between differentiated taxa. Furthermore, we characterised the discriminating power of each RAPD to recognise the different taxa using intraclass correlation coefficients. Lastly, IGS-RFLPs enabled us to assess rDNA polymorphisms on a sub-sample of individuals. On the basis of these data, a low interspecifc differentiation was found. This suggests a recent genetic divergence between the different taxa of the O. europaea complex or the occurrence of gene flow during favourable periods or because human displacements. All the olive cultivars were genetically related to the oleaster populations supporting that Mediterranean is the olive domestication area.     

Morphologic and Agronomic Diversity of Wild Genetic Resources of Medicago sativa L. Collected in Spain

One hundred and three natural populations of Medicago L. were collected in Spain, mainly from roadsides, non-irrigated or grazed lands. This germplasm was evaluated at Montpellier (France) with control cultivars and Spanish landraces under completely random block design, replicated four times, and observed for 64 qualitative or quantitative characters. Differences between natural populations and cultivated controls are highly significant, but gene flow occurs between wild and cultivated compartment and hybrid populations were identified. On the basis of multivariable analysis, the accessions were grouped into four clusters depending on their proximity with the cultivated pool to facilitate their management and ex situ conservation. The relationship between environment of the site of collection and phenotypic characteristics of the natural populations was also discussed. Different policies of conservation of these genetic resources are suggested to avoid their disappearance even when they disappeared from the other regions of the western Mediterranean. Spanish wild pool of alfalfa, also called ‘Mielga’, appears of great interest for the breeding of alfalfa because it contains a large diversity of characteristics (prostrate habit, rhizomes) linked to tolerance to grazing or drought environment. With the need for more sustainable systems in agriculture, the erosion of natural habitats and the necessity for rehabilitation of degraded ecosystems, the importance of this wild pool is really inestimable.     

Potential of earthworms,ants, millipedes,and termites for dissemination of vesicular-arbuscular mycorrhizal fungi in soil

We studied the effects of earthworms, termites, ants, and millipedes on the dissemination of vesciulararbuscular mycorrhizal (VAM) propagules. Earthworm (Lumbricus terrestris L.) casts collected from the garden were air-dried, stored, and examined for the presence of VAM fungi by inoculating the cast material onto onion plants grown in sterilized soil. VAM propagules survived for a period of 12 months. The results showed that earth-worms can contribute to the dissemination of VAM propagules. Nests of ants (Camponotus compressus Fabr.) collected from different locations were examined for the presence of VAM propagules. They harboured up to 790 infective propagules g^-1 of nest, showing that ants can be potential vectors in disseminating VAM fungi. The faecal pellets of the millipede (Phyllogonostreptus nigrolabiatus Newport) collected from the rearing tank were tested for VAM colonization. Though VAM propagules were present in the fresh faecal pellets, they lost their viability after 4 days of storage. Termitaria samples of both mound-building and subterranean termites were also examined for VAM propagules but those found were non-viable.     

4种经济鲍遗传多样性与分化的研究

应用聚丙烯酰胺凝胶电泳技术研究盘鲍(Haliotis discus discus)、皱纹盘鲍(H.discus hannai)、九孔鲍(H.diversicolor supertexta)养殖群体和杂色鲍(H.diversicolor diversicolor)自然群体遗传多样性与分化结果表明,4种经济鲍的遗传多样性较低,盘鲍群体平均每位点等位基因数目、多态位点百分数(P0.99%)、观察杂合度和期望杂合度分别为1.2、16.67、0.109和0.061,皱纹盘鲍群体分别为1.10、11.11、0.093和0.056,杂色鲍群体分别为1.44、33.33、0.106和0.118,九孔鲍群体分别为1.50、33.33、0.135和0.128。盘鲍在Mdh-1位点上符合H-W平衡标准(P>0.05),而在位点Est-3(F=-0.753)和Sod-1-1(F=-1.000)上表现出杂合子过量;皱纹盘鲍在位点Est-3符合H-W平衡标准(P>0.05),而在位点Est-3(F=-0.371)和Sod-1(F=-1.000)上表现出杂合子过量;杂色鲍在位点Est-3、Mdh-1和Amy-1上符合H-W平衡标准(P>0.05),而在位点Aat-1(F=-0.486)和Mdh-1(F=-0.210)上表现出杂合子过量,在位点Est-2(F=0.597)、Amy-1(F=0.330)和Me-1(F=1.000)上表现出杂合子缺失,九孔鲍在位点Est-3、Sdh-2、Amy-1和Mdh-1上符合H-W平衡标准(P>0.05),而在位点Aat-1(F=-0.477)和Amy-1(F=-0.149)上表现出杂合子过量,在位点Est-2(F=0.540)上表现出杂合子缺失。盘鲍和皱纹盘鲍的遗传距离为0.055,九孔鲍和杂色鲍的遗传距离为0.016。     

Genetic Structure in Tunisian Apricot, Prunus armeniaca L., Populations Propagated by Grafting: A Signature of Bottleneck Effects and Ancient Propagation by Seedlings

In order to give insights into the origin and historical selection process of Tunisian apricot propagated by grafting, 31 cultivars from three areas presenting contrasting ecological conditions – Kairouan, Testour and Ras Jbel were compared to cultivars from Europe, North America, North Africa, Turkey, Iran and China, using 234 AFLP markers. The phenetic analysis allowed to distinguish 5 clusters, the four previously defined groups: – ‘diversification’, ‘geographically adaptable’, ‘continental European’ and ‘Mediterranean’ – groups and the Tunisian one. The partitioning of genetic diversity within and between cultivar groups assessed according to the Bayesian approach and assuming Hardy–Weinberg equilibrium, showed a loss of 21.81–38.49% of genetic diversity in Tunisian apricot compared to Mediterranean and diversification groups, respectively. Genetic variation occurred within Tunisian subgroups rather than among (F_ST = 0.060) evidencing a narrow genetic pool. Mediterranean and Tunisian groups were the least differentiated. Comparing them, 24 AFLP fragments discriminated the Mediterranean group from the Tunisian group but most of them where also shared by the other groups. Strongly differentiated gene pool and low genetic diversity are probably the result of bottleneck effects linked to the occurrence of propagation by seedlings rather than by grafting during the introduction periods in the North and the Centre of Tunisia. This study points at the propagation by seedlings as an important factor which should be taken into account to understand the evolution of apricot in South Mediterranean areas.     

Sources of bioavailable trace metals for earthworms from a Zn-, Pb- and Cd-contaminated soil

The sources of bioavailable metals for earthworms were investigated in a Zn-, Pb- and Cd-contaminated soil. Selective sequential extractions (SSE) of metals were performed on soil samples with different amounts of contamination and compared with the body burden concentration of metals in two earthworm species: Aporrectodea caliginosa and Lumbricus rubellus. The most labile forms (water extractable and exchangeable) of metals were poorly related with metal accumulation by the earthworms, except for Cd, whereas the moderately available forms (acid-soluble, bound to iron oxides and organic matter) were related to the pattern of metal accumulation by earthworms. This indicates that the ingestion of metals bound to soil components is likely to be a more important uptake route than the dermal uptake of dissolved ions for metals entering the body tissue of earthworms.     

Genetic characterization of a collection of chayote, <Emphasis Type="Italic">Sechium edule</Emphasis> (Jacq.) Swartz,in Costa Rica by using isozyme markers

We established protocols for the analysis of genetic diversity in chayote (Sechium edule) by using isozyme markers, thereby determining the level of genetic diversity present in 42 accessions of chayote from Costa Rica. We obtained clear and reproducible zymograms for eight enzyme staining systems: PGM, 6-PGD, PGI, IDH, MDH, SOD, SKD, and EST, and were able to score 14 putative loci. Eight of the 14 loci examined were polymorphic. We found 35 distinct multilocus genotypes among these accessions. Five of these multilocus genotypes were homozygous for all loci. In addition, our data also revealed that most of the multilocus genotypes (24) were heterozygous for only one of the eight loci, and the rest were heterozygous for two or three loci (9 and 4 accessions, respectively). Seven multilocus genotypes were found in two different accessions. Dice similarity coefficient was used to study the relationship between accessions. This analysis, based on the presence and absence of alleles, revealed that accessions collected in the same location seldom shared the same multilocus genotype. The value of isozyme polymorphisms as tools to continue studies on the characterization of chayote is discussed.