Environmental fluctuations and the maintenance of genetic diversity in age or stage-structured populations

The ability of random fluctuations in selection to maintain genetic diversity is greatly increased when generations overlap. This result has been derived previously using genetic models with very special assumptions about the population age structure. Here we explore its robustness in more realistic population models, with very general age structure or physiological structure. For a range of genetic models (haploid, diploid, single and multilocus) we find that the condition for maintaining genetic diversity generalizes almost without change. Genetic diversity is maintained by selection if a product of the form (generation overlap)×(selection intensity)×(variability in the selection regime) is sufficiently large, where the generation overlap is measured in units of Fisher's reproductive value. This conclusion is based on a local evolutionary stability analysis, which differs from the standard “protected polymorphism” criterion for the maintenance of genetic diversity. Simulation results match the predictions from the local stability analysis, but not those from the protected polymorphism criterion. The condition obtained here for maintaining genetic diversity requires fitness fluctuations that are substantial but well within the range observed in many studies of natural populations.     

Experimental test of genetic rescue in isolated populations of brook trout

Genetic rescue is an increasingly considered conservation measure to address genetic erosion associated with habitat loss and fragmentation. The resulting gene flow from facilitating migration may improve fitness and adaptive potential, but is not without risks (e.g., outbreeding depression). Here, we conducted a test of genetic rescue by translocating ten (five of each sex) brook trout (Salvelinus fontinalis) from a single source to four nearby and isolated stream populations. To control for the demographic contribution of translocated individuals, ten resident individuals (five of each sex) were removed from each recipient population. Prior to the introduction of translocated individuals, the two smallest above‐barrier populations had substantially lower genetic diversity, and all populations had reduced effective number of breeders relative to adjacent below‐barrier populations. In the first reproductive bout following translocation, 31 of 40 (78%) translocated individuals reproduced successfully. Translocated individuals contributed to more families than expected under random mating and generally produced larger full‐sibling families. We observed relatively high (>20%) introgression in three of the four recipient populations. The translocations increased genetic diversity of recipient populations by 45% in allelic richness and 25% in expected heterozygosity. Additionally, strong evidence of hybrid vigour was observed through significantly larger body sizes of hybrid offspring relative to resident offspring in all recipient populations. Continued monitoring of these populations will test for negative fitness effects beyond the first generation. However, these results provide much‐needed experimental data to inform the potential effectiveness of genetic rescue‐motivated translocations.     

Segregation distortion for seed testa color in Mungbean (Vigna radiata L. Wilcek)

Genetic segregation experiments with plant species are commonly used for understanding the inheritance of traits. A basic assumption in these experiments is that each gamete developed from megasporogenesis has an equal chance of fusing with a gamete developed from microsporogenesis, and every zygote formed has an equal chance of survival. If gametic and/or zygotic selection occurs whereby certain gametes or zygotic combinations have a reduced chance of survival, progeny distributions are skewed and are said to exhibit segregation distortion. In this study, inheritance data are presented for the trait seed testa color segregating in large populations (more than 200 individuals) derived from closely related mungbean (Vigna radiata L. Wilcek) taxa. Segregation ratios suggested complex inheritance, including dominant and recessive epistasis. However, this genetic model was rejected in favor of a single-gene model based on evidence of segregation distortion provided by molecular marker data. The segregation distortion occurred after each generation of self-pollination from F1 thru F7 resulting in F7 phenotypic frequencies of 151:56 instead of the expected 103.5:103.5. This study highlights the value of molecular markers for understanding the inheritance of a simply inherited trait influenced by segregation distortion.     

Genetic analysis of an isolated red deer (<Emphasis Type="Italic">Cervus elaphus</Emphasis>) population showing signs of inbreeding depression

In the present study, we analysed 18 red deer specimens from a small (N = 50) and isolated population in Schleswig-Holstein, northern Germany, with respect to variability at nine polymorphic microsatellite loci and 439 bp of the mitochondrial DNA control region. Several cases of brachygnathy (shortened lower jaw), commonly associated with inbreeding depression, have been recorded in the population. Genetic variability was very low compared with other European red deer populations including the neighbouring population from which the population under study was derived some 130 years ago. The effective population size was estimated to be seven individuals corresponding to an increase in inbreeding (or a loss of heterozygosity) of 7% each generation. This value is seven times higher than the theoretical threshold level up to which natural selection is believed to counteract the fixation of deleterious alleles in the gene pool. As a consequence, the population urgently needs genetic input from other populations to overcome the negative effects of random drift and inbreeding. To our knowledge, this study is one of the first to genetically analyse a red deer population showing strong signs of inbreeding depression.     

Genetic aspects of genealogy

The supplementary historical discipline genealogy is also a supplementary genetic discipline. In its formation, genetics borrowed from genealogy some methods of pedigree analysis. In the 21th century, it started receiving contribution from computer-aided genealogy and genetic (molecular) genealogy. The former provides novel tools for genetics, while the latter, which employing genetic methods, enriches genetics with new evidence. Genealogists formulated three main laws of genealogy: the law of three generations, the law of doubling the ancestry number, and the law of declining ancestry. The significance and meaning of these laws can be fully understood only in light of genetics. For instance, a controversy between the exponential growth of the number of ancestors of an individual, i.e., the law of doubling the ancestry number, and the limited number of the humankind is explained by the presence of weak inbreeding because of sibs’ interference; the latter causes the pedigrees’ collapse, i.e., explains also the law of diminishing ancestry number. Mathematic modeling of pedigrees’ collapse presented in a number of studies showed that the number of ancestors of each individual attains maximum in a particular generation termed ancestry saturated generation. All representatives of this and preceding generation that left progeny are common ancestors of all current members of the population. In subdivided populations, these generations are more ancient than in panmictic ones, whereas in small isolates and social strata with limited numbers of partners, they are younger. The genealogical law of three generations, according to which each hundred years contain on average three generation intervals, holds for generation lengths for Y-chromosomal DNA typically equal to 31–32 years; for autosomal and mtDNA, this time is somewhat shorter. Moving along ascending lines, the number of genetically effective ancestors transmitting their DNA fragments to descendants increases far slower than the number of common ancestors, because the time to the nearest common ancestor is proportional to log2N, and the time to genetically effective ancestor, to N, where N is the population size. In relatively young populations, the number of genetically effective ancestors does not exceed the number of recombination hot spots, which is equal to 25 000–50000. In ancient African populations with weaker linkage disequilibrium, their number may be higher. In genealogy, the degree of kinship is measured by the number of births separating the individuals under comparison, and in genetics, by Wright’s coefficients of relationship (R). Genetic frames of a “large family” are limited by the average genomic differences among the members of the human population, which constitute approximately 0.1%. Conventionally it can be assumed that it is limited by relatives, associated with the members of the given nuclear family by the 7th degree of relatedness (R ∼ 0.78%). However, in the course of the HapMap project it was established that 10–30% of pairs of individuals from the same population have at least one common genome region, which they inherited from a recent common ancestor. A nuclear family, if it is not consanguinous, unites two lineages, and indirectly, a multitude of them, constituting a “suprafamily” equivalent to a population. Some problems of genealogy and related historical issues can be resolved only with the help of genetics. These problems include identification of “true” and “false” Rurikids and the problem of continuity of the Y-chromosomal lineage of the Romanov dynasty. On the other hand, computer-aided genealogy and molecular genealogy seem to be promising in resolving genetic problems connected to recombination and coalescence of genomic regions.     

Genetic variability of feral and ranch American minkNeovison vison in Poland

The diversity of 11 microsatellite loci was examined to estimate the genetic variability of ranch and feral American minkNeovison vison (Schreber, 1777) in Poland. Samples were collected from 10 mink farms (182 individuals) and from 5 areas in the north-eastern part of the country (87 individuals). At each examined locus the observed heterozygosity (H _o) was lower than the expected heterozygosity (H _e). Feral mink showed lower genetic variability than ranch mink; however, in the former group the mean value of the inbreeding coefficient (F _IS=0.306) was higher than in the latter (0.242). These results demonstrated that feral and ranch mink belong to two genetically close but separate groups. Genetic differences were identified between mink colour breeds but not between animals from particular farms. The height of the modal values of ΔK indicated the presence of four genetic clusters: (1) farmed mink sapphire, (2) farmed mink standard and pastel, (3) farmed mink pearl and (4) feral mink. Assignment of mink individuals using assignment test, STRUCTURE and GeneClass 2.0. revealed that 12–16% of the feral mink group are likely to be ranch mink escapees. It may be concluded that approximately 30 years after the start of the expansion of feral mink in north-eastern Poland, this wild-living population exists without a major input of individuals bred on fur farms.     

Postmortem Miscoding Lesions in Sequence Analysis of Human Ancient Mitochondrial DNA

Genetic miscoding lesions can cause inaccuracies during the interpretation of ancient DNA sequence data. In this study, genetic miscoding lesions were identified and assessed by cloning and direct sequencing of degraded, amplified mitochondrial DNA (mtDNA) extracted from human remains. Forty-two individuals, comprising nine collections from five geographic locations, were analyzed for the presence of DNA damage that can affect the generation of a correct mtDNA profile. In agreement with previous studies, high levels (56.5% of all damage sites) of proposed hydrolytic damage products were observed. Among these, type 2 transitions (cytosine → thymine or guanine → adenine), which are highly indicative of hydrolytic deamination, were observed in 50% of all misincorporations that occurred. In addition to hydrolytic damage products, oxidative damage products were also observed in this study and were responsible for approximately 43.5% of all misincorporations. This level of misincorporation is in contrast to previous studies characterizing miscoding lesions from the analysis of bone and teeth, where few to no oxidative damage products were observed. Of all the oxidative damage products found in this study, type 2 transversions (cytosine → adenine/guanine → thymine or cytosine → guanine/guanine → cytosine), which are commonly formed through the generation of 8-hydroxyguanine, accounted for 30.3% of all genetic miscoding lesions observed. This study identifies the previously unreported presence of oxidative DNA damage and proposes that damage to degraded DNA templates is highly specific in type, correlating with the geographic location and the taphonomic conditions of the depositional environment from which the remains are recovered. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Optimised parent selection and minimum inbreeding mating in small aquaculture breeding schemes: a simulation study

The effectiveness of low cost breeding scheme designs for small aquaculture breeding programmes were assessed for their ability to achieve genetic gain while managing inbreeding using stochastic simulation. Individuals with trait data were simulated over 15 generations with selection on a single trait. Combinations of selection methods, mating strategies and genetic evaluation options were evaluated with and without the presence of common environmental effects. An Optimal Parent Selection (OPS) method using semi-definite programming was compared with a truncation selection (TS) method. OPS constrains the rate of inbreeding while maximising genetic gain. For either selection method, mating pairs were assigned from the selected parents by either random mating (RM) or Minimum Inbreeding Mating (MIM), which used integer programming to determine mating pairs. Offspring were simulated for each mating pair with equal numbers of offspring per pair and these offspring were the candidates for selection of parents of the next generation. Inbreeding and genetic gain for each generation were averaged over 25 replicates. Combined OPS and MIM led to a similar level of genetic gain to TS and RM, but inbreeding levels were around 75% lower than TS and RM after 15 generations. Results demonstrate that it would be possible to manage inbreeding over 15 generations within small breeding programmes comprised of 30 to 40 males and 30 to 40 females with the use of OPS and MIM. Selection on breeding values computed using Best Linear Unbiased Prediction (BLUP) with all individuals genotyped to obtain pedigree information resulted in an 11% increase in genetic merit and a 90% increase in the average inbreeding coefficient of progeny after 15 generations compared with selection on raw phenotype. Genetic evaluation strategies using BLUP wherein elite individuals by raw phenotype are genotyped to obtain parentage along with a range of different samples of remaining individuals did not increase genetic progress in comparison to selection on raw phenotype. When common environmental effects on full-sib families were simulated, performance of small breeding scheme designs was little affected. This was because the majority of selection must anyway be applied within family due to inbreeding constraints.     

Two-trait selection response with marker-based assortative mating

 Marker-based assortative mating (MAM) – the mating of individuals that have similar genotypes at random marker loci – can increase selection response for a single trait by 3–8% over random mating (RM). Genetic gain is usually desired for multiple traits rather than for a single trait. My objectives in this study were to (1) compare MAM, phenotypic assortative mating (PAM), and RM of selected individuals for improving two traits and (2) determine when MAM will be most useful for improving two traits. I simulated 20 generations of selecting 32 out of 200 individuals in an F₂ population. The individuals were selected based on an index (SI) of two traits and were intermated by MAM, PAM, or RM. I studied eight genetic models that differed in three contrasts: (1) weight, number of quantitative trait loci (QTL), and heritability (h ²) for each trait; (2) linkage of QTL for each trait; and (3) trait means of the inbred parents of the F₂. For SI and the two component traits, MAM increased short-term selection response by 5–8% in six out of the eight genetic models. The MAM procedure was least effective in two genetic models, wherein the QTL for one trait were unlinked to the QTL for the other trait and the parents of the F₂ had divergent means for each trait. The loss of QTL heterozygosity was much greater with MAM than with PAM or RM. Consequently, the advantage of MAM over RM dissipated after 5–7 generations. Differences were small between selection responses with PAM and RM. The MAM procedure can enhance short-term selection response for two traits when selection is not stringent, h ² is low, and the means of the parents of the F₂ are equal for each trait. Received: 10 June 1998 / Accepted: 5 August 1998     

Effects of reforestation methods on genetic diversity of lodgepole pine: an assessment using microsatellite and randomly amplified polymorphic DNA markers

 We examined the effects of different methods of forest regeneration on the genetic diversity of lodgepole pine (Pinus contorta var ‘latifolia’) using two different DNA-based molecular markers [randomly amplified polymorphic DNA (RAPDs) and microsatellites or simple sequence repeats (SSRs)]. Genetic diversity was estimated for 30 individuals in each of four populations for the following three stand types: (1) mature lodgepole pine (>100 years); (2) 20- to 30-year-old harvested stands left for natural regeneration; (3) 20- to 30-year-old planted stands (4 stands of each type); and one group of 30 operationally produced seedlings. There was no significant effect of stand type on expected heterozygosity, although allelic richness and diversity were much higher for SSRs than for RAPDs. Expected heterozygosity ranged from 0.39 to 0.47 based on RAPDs and from 0.67 to 0.77 based on SSRs. The number of alleles per locus for SSRs ranged from 3 to 34 (mean 21.0), and there was a significant relationship between sequence repeat length and the number of alleles at a locus. Both marker types showed that over 94% of the variation was contained within the populations and that the naturally regenerated stands sampled had lower (not significant) expected heterozygosity than the planted or unharvested stands. The group of seedlings (assessed by RAPDs only) had expected heterozygosity and allele frequencies similar to those of the unharvested stands. Genetic distance measures were higher than obtained previously in the species using isozyme markers. There was no correlation between the two marker types for pair-wise genetic distances based on populations analyzed by both methods. Pair-wise genetic distance measures and an ordination of allele frequencies for both marker types showed little effect of geographic location or stand type on genetic similarity. Received: 18 August 1998 / Accepted: 17 September 1998     

Using standard nomenclature to adequately name transgenes,knockout gene alleles and any mutation associated to a genetically modified mouse strain

Mice provide an unlimited source of animal models to study mammalian gene function and human diseases. The powerful genetic modification toolbox existing for the mouse genome enables the creation of, literally, thousands of genetically modified mouse strains, carrying spontaneous or induced mutations, transgenes or knock-out/knock-in alleles which, in addition, can exist in hundreds of different genetic backgrounds. Such an immense diversity of individuals needs to be adequately annotated, to ensure that the most relevant information is kept associated with the name of each mouse line, and hence, the scientific community can correctly interpret and benefit from the reported animal model. Therefore, rules and guidelines for correctly naming genes, alleles and mouse strains are required. The Mouse Genome Informatics Database is the authoritative source of official names for mouse genes, alleles, and strains. Nomenclature follows the rules and guidelines established by the International Committee on Standardized Genetic Nomenclature for Mice. Herewith, both from the International Society for Transgenic Technologies (ISTT) and from the scientific journal Transgenic Research, we would like to encourage all our colleagues to adhere and follow adequately the standard nomenclature rules when describing mouse models. The entire scientific community using genetically modified mice in experiments will benefit.     

Glycosylation sites identified by solid-phase Edman degradation: O-linked glycosylation motifs on human glycophorin A

The human red blood cell sialoglycoprotein, glycophorin A (GpA),contains a ‘mucin-like’ extensively O-glycosylatedextracellular domain which carries the MN blood group antigens.We have revised the sites of O-glyccsylation in the extracellulardomain of GpA by automated solid-phase Edman degradation, whichallowed positive identification and quantitation of O-glycosylatedSer and Thr residues, as well as the single N-glycosylationsite. One N-linked and 16 O-linked sites were identified. Carbohydratewas absent on Ser 1, Ser14, Ser15, Ser23, Thr28 and Thr58 inGpA. We propose that the glycosyltransferases present in erythrocytesrecognize specific flanking sequences around potential O-glycosylationsites. All 16 O-glycosylation sites are explained on the basisof four motifs. Three motifs are associated with Thr-glycosylation:Xaa—Pro—Xaa—Xaa where at least one Xaa = Thr;Thr—Xaa—Xaa—Xaa where at least one Xaa = Thr;Xaa—Xaa—Thr—Xaa where at least one X = Argor Lys. The fourth motif is associated with Ser-glycosylation:Ser—Xaa—Xaa—Xaa where at least one Xaa = Ser.These simple rules explain the glycosylation (or lack of it)on 21 of 22 Ser/Thr in the extracellular domain of GpA. glycophorin A O-glycosylation motif solid-phase Edman degradation     

Genetic relationships among South-East Turkey wild barley populations and sampling strategies of Hordeum spontaneum

To assess the genetic diversity and the genetic structure of Turkish wild barley (Hordeum spontaneum Tell.) populations, 76 genotypes from ten ecologically and geographically different locations were analyzed by means of amplified fragment length polymorphism (AFLP) markers. Five primer combinations produced 187 scorable bands, of which 117 (62.6%) were polymorphic. Several population-specific and genotype-specific bands were identified, which differentiate populations or genotypes. Genetic distance, determined by Nei’s distance coefficient, varied from 0.07 to 0.21 with an average of 0.13. In the UPGMA dendrogram based on Nei genetic distances, the Hordeum spontaneum populations were separated into two major clusters. Genetic diversity was larger among (68%) than within (32%) populations. Eight AFLP bands were strongly correlated to the altitude of the collecting site, while no clear trend was detected between geographical origin and genetic diversity. Our results strongly suggest the need for a change in Hordeum spontaneum sampling strategy: more populations, rather then more individuals within population, should be sampled to appraise and safeguard genetic diversity in the wild barley gene pool.     

Estimation of long-term genetic improvement for gerbera using the best linear unbiased prediction (BLUP) procedure

Long-term genetic improvement is measured by the selection response predicted from estimates of narrow-sense heritability. Accurate estimates of selection response require partitioning the change of population mean into genetic and environmental components. A selection experiment for cut-flower yield was conducted for 16 generations in the Davis population of gerbera (Gerbera hybrida, Compositae). Breeding values were estimated for individual plants in the population using the best linear unbiased prediction (BLUP) procedure. Genetic change in each generation was calculated from the breeding values of individual plants. The results of this study indicate that long-term selection was successful and necessary for the genetic improvement in cut-flower yield. Genetic improvement in mean breeding value over 16 generations was 33 flowers. Mean breeding values increased monotonically with an S-shape pattern while environmental effects fluctuated from generation to generation. Results predict that cut-flower yield in the Davis population of gerbera will continue to respond to selection.     

Genetic liability to schizophrenia in Oceanic Palau: a search in the affected and maternal generation

While liability to schizophrenia (Scz) is due to genetic and environmental factors, specific factors are largely unknown. We postulate a two-hit model for Scz, in which initial liability is generated during fetal brain development: this “hit” is precipitated by environmental stressors biologically interacting with maternal genetic vulnerability to the stress. Additional liability to Scz is generated by individual genetic vulnerability. To evaluate these putative levels of vulnerability, we search in the genome of both affected individuals and their mothers for variation that differs, statistically, from that in the general population. For parental analyses, mothers were treated as “affected,” rather than their offspring, and the fathers were treated as “controls”. We used a sample from the Palauan population: 175 individuals diagnosed with Scz, broadly defined; 87 mothers and 45 fathers of affected individuals. Pedigree and diagnostic data were available on 2,953 living and deceased subjects. DNA from 553 individuals was genotyped for short tandem repeats (STR) spaced approximately every 10 cM across the genome. We tested for association between affection status and STR alleles; such an approach was reasonable, despite the widely spaced markers, because this population has far-ranging linkage disequilibrium (LD). Results for the truly affected individuals were modest, whereas results from the maternal generation were promising. For a recessive model and a test for excess allele matching across mothers, significant findings occurred for D20S481, D10S1221, D6S1021, D13S317, and D18S976. Regions in which at least two adjacent markers produced substantial association statistics include 2p12-11.2, 2q24.1-32.1, 6q12-14.1, 10q23.2-24.21, 12q23.2-24.21 and 17q23.2-23.3.     

Population genetics of the freshwater mussel, <Emphasis Type="Italic">Amblema plicata</Emphasis> (Say 1817) (Bivalvia: Unionidae): Evidence of high dispersal and post-glacial colonization

Over 70% of North American freshwater mussel species (families Unionidae and Margaritiferidae) are listed as threatened or endangered. Knowledge of the genetic structure of target species is essential for the development of effective conservation plans. Because Ambelma plicata is a common species, its population genetic structure is likely to be relatively intact, making it a logical model species for investigations of freshwater mussel population genetics. Using mtDNA and allozymes, we determined the genotypes of 170+ individuals in each of three distinct drainages: Lake Erie, Ohio River, and the Lower Mississippi River. Overall, within-population variation increased significantly from north to south, with unique haplotypes and allele frequencies in the Kiamichi River (Lower Mississippi River drainage). Genetic diversity was relatively low in the Strawberry River (Lower Mississippi River drainage), and in the Lake Erie drainage. We calculated significant among-population structure using both molecular markers (A.p. Φ_st = 0.15, θ_st = 0.12). Using a hierarchical approach, we found low genetic structure among rivers and drainages separated by large geographic distances, indicating high effective population size and/or highly vagile fish hosts for this species. Genetic structure in the Lake Erie drainage was similar to that in the Ohio River, and indicates that northern populations were founded from at least two glacial refugia following the Pleistocene. Conservation of genetic diversity in Amblema plicata and other mussel species with similar genetic structure should focus on protection of a number of individual populations, especially those in southern rivers.     

Social heterosis and the maintenance of genetic diversity

Genetic diversity in species is often high in spite of directional selection or strong genetic drift. One resolution to this paradox may be through fitness benefits arising from interactions of genetically diverse individuals. Advantageous phenotypes that are impossible in single individuals (e.g. being simultaneously bold and shy) can be expressed by groups composed of genetically different individuals. Genetic diversity, therefore, can produce mutualistic benefits shared by all group members. We define this effect as 'social heterosis', and mathematically demonstrate maintenance of allelic diversity when diverse groups or neighbourhoods are more reproductively successful than homogenous ones. Through social heterosis, genetic diversity persists without: frequency dependence within groups, migration, balancing selection, genetic linkages, overdominance, antagonistic pleiotropy or nonrandom allele assortment. Social heterosis may also offer an alternative evolutionary pathway to cooperation that does not require clustering of related individuals, nepotistic favouritism towards kin, or overt reciprocity.     

Cost‐effective development of highly polymorphic microsatellite in Japanese quail facilitated by next‐generation sequencing

Next‐generation sequencing technologies permit rapid and cost‐effective identification of numerous putative microsatellite loci. Here, from the genome sequences of Japanese quail, we developed microsatellite markers containing dinucleotide repeats and employed these for characterisation of genetic diversity and population structure. A total of 385 individuals from 12 experimental and one wild‐derived Japanese quail lines were genotyped with newly developed autosomal markers. The maximum number of alleles, expected heterozygosity and polymorphic information content (PIC) per locus were 10, 0.80 and 0.77 respectively. Approximately half of the markers were highly informative (PIC ≥ 0.50). The mean number of alleles per locus and observed heterozygosity within a line were in the range of 1.3–4.1 and 0.11–0.53 respectively. Compared with the wild‐derived line, genetic diversity levels were low in the experimental lines. Genetic differentiation (F_ST) between all pairs of the lines ranged from 0.13 to 0.83. Genetic clustering analyses based on multilocus genotypes of individuals showed that most individuals formed clearly defined clusters corresponding to the origins of the lines. These results suggest that Japanese quail experimental lines are highly structured. Microsatellite markers developed in this study may be effective for future genetic studies of Japanese quail.     

Genetic diversity and genetic structure of different populations of the endangered species Davidia involucrata in China detected by inter-simple sequence repeat analysis

Dove tree (Davidia involucrate) is a Tertiary relic species endemic to China and is reputed to be a ‘living fossil’ in the plant kingdom. Genetic diversity and genetic structure of this species were analyzed for its conservation and management, using inter-simple sequence repeat (ISSR) data obtained from eight populations distributed throughout seven provinces of China. A relatively high level of genetic diversity, at both population and species levels, was detected using the POPGENE software. Analysis of molecular variance (AMOVA) revealed a moderate level of among-population variation (i.e., 33.21%). The genetic structure of dove tree was closely consistent with their isolated topographical distribution region based on the results of the STRUCTURE, POPGENE-UPGMA and PCA analysis. It is postulated that the relatively high level of genetic diversity has been maintained because of: (a) the original wild geographical distribution, (b) propagation through outcrossing seeds or root suckers, (c) the longevity of individuals and (d) the relatively little human disturbance. Genetic drift and restricted gene are important factors affecting genetic differentiation. There was no significant correlation between geographical distances and a pairwise comparison with genetic distances, as analyzed by the Mantel test, but the clustering result of genetic diversity was consistent with their isolated topographical distribution regions. Thus, maintaining the stable special habitats associated with this species is recommended for the in situ conservation. Furthermore, it is important to develop an effective seed germination system for the maintenance of an ex situ conservation pool of the germplasm resources.     

M13 DNA fingerprinting can be used in studies on phenotypic reversions of forest tree mutants

 Solitary revertants which have been observed on single mutant tree individuals have up to now been believed to be grow-through cells belonging to the rootstock on which they are commonly grafted. In this study three different phenotypically visible mutants revealing revertant shoots on the same tree were chosen for genetic analysis. The mutant Quercus robur L. ‘argenteomarginata’ was grafted on a normal rootstock, an individual of Carpinus betulus L. var. quercifolia Desf. as well as an individual of Picea glauca (Moench) Voss. ‘conica’ are supposed to have grown from seeds. By means of a highly specific M13 PCR fingerprinting technique the mutant and revertant tissues were analysed in comparison to different individuals of each of the species. With the grafted mutant, cambium tissue of the rootstock was also investigated. Whereas conspecific individuals could be clearly distinguished from each other, mutant and revertant tissues revealed the same banding patterns for each of the three trees. In case of the grafted mutant, the fingerprint obtained from cambium tissue of the rootstock was clearly different from the pattern of mutant and revertant tissue. Results demonstrate the potential of the tool for genetic differentiation between individuals of three tree species hence in the case of the grafted mutant, the hypothesis that the observed reversion is caused by a grow-through of the rootstock is rejected. Furthermore, identical fingerprints of mutant and revertant tissue support identical genetic background of the tissues excluding the gene(s) responsible of the mutation. Possible causes of mutations and reversions regarding the three mutant trees are discussed. Received: 15 September 1997 / Accepted: 24 November 1997