Lack Of Genetic Variation Research Articles

Non‐invasive genotyping of the endangered Apennine brown bear: a case study not to let one's hair down

AbstractIndividual identification was assessed for 30 brown bears (Ursus arctos) from the endangered Apennine population in central Italy, mostly through non‐invasive sampling. Shed hairs were used as a source of DNA to obtain single genotype profiling at 12 microsatellite loci. Average expected heterozygosity (0.438) and mean number of alleles per locus (2.2) showed that the level of genetic diversity was one of the lowest recorded for brown bear populations across their European and North American ranges. A large portion of the original genetic variation may have been lost through random genetic drift during the recent period of isolation. The level of genetic variability proved sufficient to identify the bears individually by using nine microsatellite loci. The probability that two animals shared by chance the same multilocus genotype was estimated to be 1 in 100. Despite the recent history of small population size, the average relatedness indicated that the majority of individuals are not first‐order relatives. Simulated paternity tests showed that a 12‐loci genotype may be necessary to assign paternity with an 80–95% confidence level. Lack of genetic diversity, as well as the maintenance of an adequately effective number, may seriously jeopardise the long‐term survival of this population. Furthermore, high mortality rates, poaching and encroachment by human activities represent immediate, urgent concerns. A population increase through enforced protection and habitat restoration is recommended. Presently, restocking with bears from other source populations should be discouraged to avoid genetic extinction. Non‐invasive sampling provided reliable population and individual genetic data. Microsatellite genotyping proved a valuable genetic tagging method and a feasible alternative to conventional field counts for the brown bear in central Italy.

Dispersal of the Ponto-Caspian amphipod Echinogammarus ischnus: invasion waves from the Pleistocene to the present.

The geographical range of the amphipod crustacean Echinogammarus ischnus has expanded over the past century from the Ponto-Caspian region to Western Europe, the Baltic Sea, and the Great Lakes of North America. The present study explores the phylogeographic patterns of this amphipod across its current distribution, based on an examination of nucleotide diversity in the mitochondrial cytochrome c oxidase subunit I (COI) gene. Marked genetic divergence exists among populations of E. ischnus from the Black and Caspian Seas, as well as those from the drainage system of the Black Sea. This divergence suggests the prolonged geographic isolation of these native populations, reflecting the limited dispersal capability of E. ischnus. By contrast, invading populations are characterized by a lack of genetic variation; a single mitochondrial genotype of Black Sea origin has colonized sites from the Rhine River to North America. The dispersal pattern in E. ischnus is very similar to that in the Ponto-Caspian cladoceran Cercopagis pengoi. Despite their contrasting life history strategies, these invading species followed the same route of invasion from the northern Black Sea to the Baltic Sea region, and subsequently to North America.

Genetic Variability in Six Ecotypes of a Mangrove, Acanthus ilicifolius L., as Revealed by Genome Size and RAPD Markers

Genomic DNA from 6 representative individuals of Acanthus ilicifolius from 6 mangrove ecotypes of north-easten India was analyzed for RAPDs using 10 primers. A total of 158 amplification products were observed with an average 15.8 amplicons per primer out of which 51.89% were polymorphic. The polymorphic RAPDs were pooled and clustering was carried out based on mean similarities for individual populations. The dendogram showed group of ecotypes, which are near to each other into specific clusters. These results demonstrated that considerable inter-ecotype genetic variation exists in A. ilicifolius and this lack of genetic variation is not the reason for the morphological uniformity observed across the range of the species. At the inter-ecotype level ∼17 of RAPD loci (56.66%) detected through the use of 10 primers. The somatic cells of the species displayed 44 chromosomes, with no numerical changes at inter-ecotype levels with few alterations in chromosome type. The genome size further added a significant variability in the context of inter-ecotype divergence.

Association of an 11-12 kDa protease-resistant prion protein fragment with subtypes of dura graft-associated Creutzfeldt-Jakob disease and other prion diseases.

Creutzfeldt-Jakob disease can develop in subjects given a cadaveric dura mater graft (dCJD). This disease has a phenotypic heterogeneity despite the lack of genetic variation. Numerous plaque-type prion protein (PrP) deposits are found in the brain of some but not all subjects; hence, there may be two subtypes of this clinical entity. To validate dCJD subtypes further, we carried out a larger-scale clinicopathological analysis and typing of protease-resistant PrP (PrP(Sc)) in dCJD cases. Cases with plaque-type PrP deposits (p-dCJD) were shown to be distinct from those without PrP plaques (np-dCJD), from several clinicopathological aspects. Analysis of PrP(Sc) revealed that, while the major PrP(Sc) species from both subtypes was of 21 kDa after deglycosylation (type 1 PrP(Sc)), a C-terminal PrP fragment of 11-12 kDa (fPrP11-12) was associated with np-dCJD but not with p-dCJD. The disease type-specific association of fPrP11-12 was also observed in subjects with other prion diseases. An fPrP11-12-like C-terminal PrP fragment was detected in brain lysates from patients associated with fPrP11-12, but not from patients or normal subjects unassociated with fPrP11-12. Results indicated that fPrP was produced by CJD-associated processes in vivo. The present data provide several lines of evidence that support the need for subtyping of dCJD and contribute to the understanding of the processing of disease-specific PrP species. The unique relationship of fPrP11-12 with CJD phenotype supports the view that the phenotypic heterogeneity of CJD is related to the formation of different types of disease-specific PrP and fragments thereof.

Drought in an evolutionary context: molecular variability in Flannelmouth Sucker (Catostomus latipinnis) from the Colorado River Basin of western North America

Summary 1. Fishes can often rebound numerically and distributionally from short‐term (i.e. seasonal) drought, yet their capacity to recover from decades or centuries of drought is less apparent. An exceedingly warm and dry period swept the intermontane west of North America ca. 7500 years BP, concomitant with an abrupt extinction of >35 mammal species. Were larger fishes in mainstem rivers also impacted by this drought?2. The Colorado River Basin encompasses seven states in western North America and drains 600 000 km2. Its endemic mainstem fish community is ancient (i.e. Miocene) but depauperate.3. We evaluated one widely distributed candidate species (flannelmouth sucker, Catostomus latipinnis) for basin‐wide genetic and geographic structure at three fast‐evolving mitochondrial (mt) DNA genes, ND2 with 589 bp and ATPase 8 and 6 with 642 bp. It is hypothesized that a concomitant signature would be present in the mtDNA of this species, if indeed it had been seriously bottlenecked by post‐Pleistocene drought. A total of 352 individuals were sequenced from 24 populations (4–40 individuals/population; average of 14.7).4. Only 49 unique haplotypes were found, 53% of which represented single individuals. Haplotype diversity was high (0.905 ± 0.007) whereas nucleotide diversity was low (0.002 ± 0.000).5. A significant and positive geographical cline (P < 0.001) in nucleotide diversity was observed as sampling locations progressed upstream from southwest to northeast. These results divided the Colorado River Basin into three reaches: the lower reach with six populations and 83 individuals; the upper reach with seven populations and 83 individuals; and the middle reach with 11 populations and 186 individuals. An analysis of molecular variance (amova) revealed that 81.5% of the total genetic variation was within populations, 16% among populations within reaches and 2.5% among reaches. Only the last was significant. Populations from the three reaches diverged from one another by 3400–11 000 years BP. Haplotype distribution suggested populations in the upper Colorado River are expanding.6. The lack of genetic variation and recent coalescence of lineages in C. latipinnis are unusual given its fossil history, broad geographical sampling, the rapid rate of mtDNA evolution and the number (and evolutionary rate) of the genes examined. The most parsimonious explanation for these data is a rapid expansion following a recent period of low effective population size at the end of the Pleistocene.7. The intense drought is suggested at the end of the Pleistocene (late‐to‐mid‐Holocene), severely impacted not only large mammals but also larger fishes in western North American rivers. These perspectives have important implications for management of endangered and threatened species in this region.

Phylogenetic analysis of Asplenium subgenus Ceterach (Pteridophyta: Aspleniaceae) based on plastid and nuclear ribosomal ITS DNA sequences

Phylogenetic relationships among 20 taxa of the fern genus Asplenium subgenus Ceterach (Filicopsida, represented by 73 accessions) were investigated using DNA sequence data from the nuclear ribosomal internal transcribed spacers (ITS nDNA) and plastid trnL-F intergenic spacer. In addition, a single sample per taxon was used in an analysis of the plastid rbcL gene. Chromosome counts were determined for all the samples, and these demonstrated a range from diploid to octoploid. Analyses of the DNA sequence data indicated that Asplenium subgenus Ceterach is polyphyletic, implicating homoplasy in the characters previously used to circumscribe this taxon. Plastid trnL-F and rbcL analyses resulted in identical tree topologies. The trees produced from the separate plastid and nuclear matrices agree in (1) the recognition of identical groups of accessions corresponding to A. dalhousiae, A. ceterach, A. aureum, A. cordatum, A. phillipsianum, and A. haughtonii; (2) the division of A. subg. Ceterach into two subclades, a Eurasian-Macaronesian and a strictly African alliance; (3) the position of A. dalhousiae as a member of the former subclade; (4) the lack of genetic variation in A. cordatum despite its morphological variability; and (5) the clustering of each autopolyploid with their diploid ancestor. However, the plastid and nuclear trees differ in their placement of A. haughtonii and A. dalhousiae, which might be due to different evolutionary histories of nuclear and plastid genomes, and is possibly an indication of ancient hybridization. The analyses confirm the existence of several strictly African taxa. Asplenium phillipsianum and A. cordatum each form species complexes of diploid and autopolyploid taxa, from which a third, morphologically intermediate, allotetraploid species has originated. Asplenium haughtonii is a distinct endemic species from Saint Helena. The maternally inherited plastid sequences support the hypothesis that A. aureum is an ancestor of A. lolegnamense and of A. octoploideum. Because gene conversion did not eliminate divergent ITS alleles in the allopolyploids, their reticulate ancestry could be demonstrated. Biparentally inherited nrITS sequences support the allopolyploid status of A. aureum, A. lolegnamense, and A. punjabense, indicating they share the ancestral A. javorkeanum genome.

One wolf wonder

One of the key problems facing the management of endangered species is the possibility that dwindling populations become isolated and inbred, further threatening their existence. There can be few species that have had a tougher recent time of it than the grey wolf (Canis lupus) which has been subject of intense hunting and extermination since the nineteenth century. In the 1960s the grey wolf was finally considered extinct on the Scandinavian peninsular. But 20 years ago, a small breeding pack was discovered in southern Scandinavia, more than 900 kilometres from the nearest known populations in Finland and Russia to the east, sparking controversy as to their origin. Preliminary studies revealed a lack of genetic variability in the fewer than 10 individuals comprising the pack during the 1980s. But after 1991, with no changes in their circumstances and continuing legal and illegal hunting, the population began to grow exponentially to a current position of 10–11 breeding packs comprising a total population of around 90–100. Intrigued by these findings, a team led by Carles Vila, at the University of Uppsala, and colleagues in Finland, Italy, Sweden and Norway, began a detailed genetic study of the expanding population. Using a variety of molecular tools, including maternally, paternally and bi-parentally inherited markers, the researchers began to track the population's origins. Lack of genetic variation in the group led the researchers to believe that a single pair of wolves originally founded it. The analyses also suggested that the pair were more closely related to the current eastern populations than the historical Scandinavian types. But after 1991, the researchers found a sudden increase in genetic variability in subsequently tested wolves. As they report in the Proceedings of the Royal Society, London Series B (published online), they concluded that a single male immigrant that had mated within the group had led to a boost in genetic diversity and mating success. Only immigrants that successfully reproduce within the population can contribute to the rescue of the population. The researchers found evidence of another immigrant wolf in Scandinavia in the early 1980s but it failed to reproduce and so did not contribute to the genetic make-up of the population. Such a dramatic improvement in genetic variability and viability, when an outsider breeds within a bottlenecked population, will be a cheering result for other conservationists and population biologists concerned about the genetic health of isolated and inbred populations: in this case at least, just a single outsider can make all the difference.

The effects of plant genetic variation and soil nutrients on secondary chemistry and growth in a shrubby willow, Salix sericea: patterns and constraints on the evolution of resistance traits

Investigators often examine the factors—genetic or environmental—that determine the concentrations of secondary chemicals and growth, but few have examined both simultaneously. We used a factorial genetic design and manipulated nutrient availability to Salix sericea (Salicaceae) in order to quantify: (1) genetic variation, plasticity, and genetic variation in plasticity for growth rate and the concentrations of two phenolic glycosides (salicortin and 2′-cinnamoylsalicortin), and (2) tradeoffs between secondary chemistry and growth rate, and between the two phenolic glycosides. We found genetic variation and genetic variation in plasticity for both chemicals but not for growth rate. Nutrient fertilization enhanced growth and decreased salicortin concentration. More importantly, nutrient environment affected the expression of genetic variation. Heritability was significant only in the medium (both phenolic glycosides) and in the high (2′-cinnamoylsalicortin only) fertilizer treatments, and there was significant genetic variation in plasticity. There was no evidence suggesting that selection for increased chemical concentration would occur at the expense of growth rate. Finally, it appears that selection in favor of one chemical would result in positive correlational selection for the other. Overall, the evolution of these traits might be constrained by a lack of genetic variation in some environments, but not by negative genetic correlations between the different traits.

Inheritance of leaf rust resistance in the wheat cultivars AC Majestic, AC Splendor, and AC Karma

The wheat cultivars AC Majestic, AC Splendor, and AC Karma were developed and licensed for production in western Canada in the mid-1990s. Leaf rust, caused by Puccinia triticina, is an important pathogen of wheat throughout North America. Virulent isolates of P. triticina are selected and increase following the release of wheats with specific resistance genes, which eventually reduces the effectiveness of the resistance. Knowledge of the genes that condition leaf rust resistance in wheat makes it easier to add additional resistance genes to breeding germplasm. The objective of this study was to identify the leaf rust resistance genes in these three cultivars. The three cultivars were crossed with the susceptible wheat 'Thatcher', and the F1 plants were backcrossed to 'Thatcher'. The backcross F2 (BCF2) families were tested for segregation of leaf rust resistance in seedling tests with specific P. triticina isolates. The BCF2 families were also tested for segregation of leaf rust resistance as adult plants in a field rust nursery that had been inoculated with a mixture of P. triticina virulence phenotypes. 'AC Majestic' was determined to have the seedling resistance gene Lr16 and the adult plant resistance gene Lr13. 'AC Splendor' was determined to have Lr13, Lr16, and the adult plant resistance gene Lr34. 'AC Karma' was determined to have Lr13, Lr16, and the adult plant resistance gene LrTb. All three cultivars had genes Lr13 and Lr16, which reflect a lack of genetic diversity for leaf rust resistance in western Canada spring wheats. The results of the study indicate that additional leaf rust resistance genes need to be crossed into the spring wheat germplasm to provide new cultivars with high levels of leaf rust resistance.

Lack of Genetic Diversity in Salamandra lanzai Revealed by CytochromebGene Sequences

The black salamander, Salamandra lanzai, exists in isolated and fragmented populations in the Cottian Alps. To examine the degree of intra- and interpopulation divergence, mitochondrial cytochrome b sequences were obtained from samples representing all populations of S. lanzai. No genetic variation was observed either within or among populations. The presence of a single lineage suggests historical explanations closely related to Pleistocene events.

Yield response of rice ( Oryza sativa L.) genotypes to drought under rainfed lowland : 3. Plant factors contributing to drought resistance

A series of experiments were conducted in drought-prone northeast Thailand to examine the magnitude of yield responses of diverse genotypes to drought stress environments and to identify traits that may confer drought resistance to rainfed lowland rice. One hundred and twenty eight genotypes were grown under non-stress and four different types of drought stress conditions. Under severe drought conditions, the maintenance of PWP of genotypes played a significant role in determining final grain yield. Because of their smaller plant size (lower total dry matter at anthesis) genotypes that extracted less soil water during the early stages of the drought period, tended to maintain higher PWP and had a higher fertile panicle percentage, filled grain percentage and final grain yield than other genotypes. PWP was correlated with delay in flowering ( r=−0.387) indicating that the latter could be used as a measure of water potential under stress. Genotypes with well-developed root systems extracted water too rapidly and experienced severe water stress at flowering. RPR which showed smaller coefficient of variation was more useful than root mass density in identifying genotypes with large root system. Under less severe and prolonged drought conditions, genotypes that could achieve higher plant dry matter at anthesis were desirable. They had less delay in flowering, higher grain yield and higher drought response index, indicating the importance of ability to grow during the prolonged stress period. Other shoot characters (osmotic potential, leaf temperature, leaf rolling, leaf death) had little effect on grain yield under different drought conditions. This was associated with a lack of genetic variation and difficulty in estimating trait values precisely. Under mild stress conditions (yield loss less than 50%), there was no significant relationship between the measured drought characters and grain yield. Under these mild drought conditions, yield is determined more by yield potential and phenotype than by drought resistant mechanisms per se.

Population genetic structure of Potamogeton anguillanus in Lake Shinji, Japan

Enzyme electrophoresis was performed to investigate the genetic variation of Potamogeton anguillanus Koidz. in Lake Shinji, Shimane Prefecture, Japan. The collection was made in six local populations along the coast of the lake, and a total of 78 shoot samples were obtained. No variation among samples occurred in the six enzymes analyzed, and the whole population in Lake Shinji was proved to consist of only a single multienzyme phenotype. Clonal growth without sexual reproduction may have resulted in the genetic uniformity. The implication of the lack of genetic variation is briefly discussed from the viewpoint of conservation of the species in Lake Shinji.

Inbreeding and Extinction in Island Populations: a Cautionary Note

Extinction rates may appear generally higher on island than mainland populations, but the reason for this difference is controversial (e.g., Pimm 1991). Characteristically, small island populations are susceptible to demographic and environmental stochasticity (e.g., Pimm 1991), but genetic factors such as inbreeding and lack of genetic variation may also decrease their viability (e.g., Frankham 1995). For example, there is compelling evidence that inbreeding depresses individual reproductive success in typically out-breeding domestic plants and animals (e.g., Wright 1977; Falconer 1989; Frankham 1999) and captive populations of vertebrate wildlife (e.g., Ralls et al. 1988). But drawing general conclusions from individual species requires quantitative comparative analyses, rather than appeals to particular studies. Frankham (1998) addresses this issue by using interspecific comparative data to test several hypotheses derived from theoretical population genetics. In particular, Frankham (1998) claims that inbreeding coefficients are significantly higher in endemic than nonendemic island populations and that many island populations show levels of inbreeding associated with elevated extinction rates in domestic and laboratory species. Such interspecific comparative studies and meta-analyses of different populations are useful techniques to address apparently inconsistent empirical evidence (e.g., Harvey 1996; Frankham 1999). However, phylogenetic information should be taken into account in such analyses (Harvey & Pagel 1991), because closely related species share many traits as a result of common ancestory (Harvey 1996). Unfortunately, Frankham (1998) did not incorporate phylogenetic data into his analyses; hence, his conclusions may be misleading. We reanalyzed the data presented by Frankham (1998), correcting for taxonomic relationships. In particular, we explored the relationship between inbreeding and population viability and compared the inbreeding coeffi-

Perspective: reverse evolution.

For some time, the reversibility of evolution was primarily discussed in terms of comparative patterns. Only recently has this problem been studied using experimental evolution over shorter evolutionary time frames. This has raised questions of definition, experimental procedure, and the hypotheses being tested. Experimental evolution has provided evidence for multiple population genetic mechanisms in reverse evolution, including pleiotropy and mutation accumulation. It has also pointed to genetic factors that might prevent reverse evolution, such as a lack of genetic variability, epistasis, and differential genotype-by-environment interactions. The main focus of this perspective is on laboratory studies and their relevance to the genetics of reverse evolution. We discuss reverse evolution experiments with Drosophila, bacterial, and viral populations. Field studies of the reverse evolution of melanism in the peppered moth are also reviewed.

Origin and conservation genetics of the threatened Ute ladies'‐tresses,Spiranthes diluvialis(Orchidaceae)

The Ute ladies'-tresses, Spiranthes diluvialis, is listed as a threatened orchid in west-central United States by the Federal government. Information on its origin and patterns of genetic variation is needed to develop effective conservation strategies for this species. DNA sequencing and polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) was used to evaluate genetic variation and structure of 23 populations of S. diluvialis. In addition, four congeneric species were analyzed to determine possible origins of the putative allotetraploid S. diluvialis. DNA sequencing and PCR-RFLP analysis of the nuclear ribosomal internal transcribed spacer (ITS) and mitochondrial and chloroplast DNA noncoding regions revealed no genetic variation within or among populations of S. diluvialis. DNA sequencing revealed that S. diluvialis has rDNA of both S. magnicamporum and S. romanzoffiana, supporting the proposed origin of the allotetraploid. Parsimony and maximum likelihood analyses of cpDNA and mtDNA sequences revealed that these S. diluvialis organellar sequences were most closely related to those of S. romanzoffiana, providing evidence that the latter species is the maternal parent of S. diluvialis. The lack of genetic diversity is significant for the development of a long-term conservation strategy for S. diluvialis.

Genetic homogeneity in the seagrass Cymodocea nodosa at its northern Atlantic limit revealed through RAPD

Random amplified polymorphic DNA (RAPD) markers were used to analyse the genetic variability of the dioecious seagrass Cymodocea nodosa Ucria (Ascherson) in the Ria Formosa lagoon, Portugal, the species' northern limit in the Atlantic. Three individuals from each of 6 meadows were genotyped with 28 primers. Meadows described previ- ously as having flower marks were compared with meadows where flowers did not occur. A single polymorphic band, spe- cific for one meadow, was observed in a total of 177 fragments. The lack of genetic variability among meadows both with and without flower indicates that flower production is not associ- ated with a higher level of genetic variation. The genetic homogeneity of C. nodosa in the Ria Formosa suggests a founder effect, produced by a single or a limited number of migrants composing the colonising gene pool. This hypothesis is supported by the geographic isolation from other popula- tions as the nearest populations lie more than 300 km away from the Ria Formosa. The lack of reproductive success of C. nodosa in Ria Formosa natural park and its low genetic vari- ability are important factors in the conservation of this species since recolonisation can only occur through vegetative growth.

Amount and structure of intra- and interspecific genetic variation in the moss genus Polytrichum.

Allozyme electrophoresis was used to determine amount and structure of genetic variation within and between five congeneric haploid moss species: Polytrichum formosum, P. commune, P. uliginosum, P. piliferum and P. juniperinum. For the different species, gene diversity within populations (HS) ranged from very low (0.025) to moderate values (0.127), being, on average, lower than those observed for vascular plants and many other moss species. Polytrichum piliferum and P. juniperinum showed significantly higher levels of HS than the other species examined, which possibly might be explained by sexual reproduction being more prevalent in these two species, that often live in more dynamic habitats, where turnover of individuals is more frequent. Genetic variability was observed to be structured in contrasting ways at different levels. At the intraspecific level genetic differentiation among populations of most Polytrichum species was low, FST </= 0.1, indicating a considerable degree of gene flow by wind-dispersed spores over substantial distances. At the interspecific level strong divergence, genetic identities being on average I=0.222, was observed between most species studied, despite low levels of divergence at the morphological level. These I-values are significantly lower than observed for congeneric vascular plant species and most congeneric bryophyte species. This suggests that the morphological conservatism is not due to lack of genetic variability and evolutionary potential.

Clonality and sexual reproductive failure in remnant populations of Santalum lanceolatum (Santalaceae)

Habitat fragmentation can have important conservation consequences for clonal plant species that possess self-incompatibility mechanisms, as lack of genetic variability within remnant populations may result in sexual reproductive failure. Allozymes and RAPDs were used in this study to determine the extent of clonality in remnant Victorian populations of the northern sandalwood, Santalum lanceolatum (Santalaceae), a species that has been heavily wild-harvested. S. lanceolatum can reproduce asexually by root suckers, and each population was identified as a unique single clone composed of numerous ramets of a single genet. Examination of pollination and fruit set indicated that little or no sexual reproduction was occurring in the remnants, due to pollen sterility in one population and self-incompatibility or pistil dysfunction in others. Clonality, genetic isolation and sexual reproductive failure indicate that preservation of each population, and possibly the establishment of new ones, should be objectives of the conservation strategy for the S. lanceolatum remnants.

Genetic diversity of the epiphytic bryophyte Leucodon sciuroides in formerly glaciated versus nonglaciated parts of Europe.

Twelve populations of the epiphytic bryophyte Leucodon sciuroides from three major regions representing formerly glaciated and nonglaciated regions of Europe were screened for polymorphisms at 15 putative isozyme loci. The populations clustered into three distinct groups consisting of: (i) a single population from Crete, representing a cryptic unknown taxon; (ii) four Scandinavian populations and two populations from northern Greece; and (iii) the remaining populations from mainland Greece and Crete. The Scandinavian populations were genetically depleted compared with most Greek populations, thus fitting the expectation of generally lower levels of variation in formerly glaciated areas. The transition zone between genetically diverse and depleted populations appears to be located through northern Greece, coinciding with the northern limit of the Mediterranean region. This indicates that genetic variation was lost in populations at the northern limit of glacial refugia. The two groups of populations fit a progenitor-derivative model. They also have contrasting reproductive strategies: the Mediterranean populations reproduce sexually, whereas the other populations propagate vegetatively. Epiphytic species, growing on substrates that are limited in space and time, appear to be especially vulnerable to loss of genetic variation. Lack of genetic variation and therefore low adaptability to increased levels of atmospheric pollution may explain why many epiphytic lichen and bryophytes, including L. sciuroides, are declining over much of Europe.

Random amplified polymorphic DNA (RAPD) analysis in Indian mung bean (Vigna radiata (L.) Wilczek) cultivars.

Greengram [Vigna radiata (L.) Wilczek], also known as mung bean, widely cultivated in a large number of countries, is an important pulse crop of Asia and is considered one of the ancestral species of the genus Vigna. Since yields of greengram have remained low across subtropical and tropical Asia, it is important to estimate genetic diversity in existing cultivars in order to see if the lack of genetic variability might be a constraining factor. In this study, 32 Indian cultivars of greengram were subjected to random amplified polymorphic DNA (RAPD) analysis using 21 decamer primers. A total of 267 amplification products were formed at an average of 12.71 per primer with an overall polymorphism of 64%. The extent of polymorphism was moderate to low. Jaccard similarity coefficient values ranged from 0.65 to 0.92. The cluster analysis resulted in mainly three clusters revealing greater homology between cultivars released from the same source. The results of principal components analysis also substantiated this conclusion. The close genetic similarity between the cultivars could be explained due to the high degree of commonness in their pedigrees. The narrow genetic base of the greengram cultivars revealed in the present analysis emphasises the need to exploit the large germplasm collections having diverse morphoagronomic traits in cultivar improvement programs.