Genetic variation in low elevation Douglas-fir of British Columbia and its relevance to gene conservation

Patterns of variation were studied at 20 isozyme loci in 49 coastal, low-elevation Douglas-fir populations in SW British Columbia and NW Washington State. Several components of variation were estimated for each population including the number of alleles per locus N _a, number of alleles per polymorphic locus N _a(95), inbreeding F, heterozygosity H, and population divergence D. F was near zero indicating nearly complete outcrossing within populations. H was quite high (16%) and in aecord with previous studies of Douglas-fir. D values were low (equivalent to Wrights F _ST of 0.08) indicating levels of gene flow sufficient to largely homogenize populations. The parameters of diversity N _a, N _a(95), H, and D showed little intercorrelation across populations. A homogenous pattern of genetic relationship among populations was shown by the clustering of populations based on their inferred relationship, and by the principal components of the matrix of inferred genetic relationship. Because of the complex nature of gene diversity and the continuous nature of population differentiation in Douglas-fir, it is difficult with isozyme markers to identify specific populations of value for genetic conservation in this species.This paper is dedicated to J.C. Heaman on the occasion of his retirement.     

Coexistence of rotifer (Brachionus plicatilis) clones in Soda Lake,Nevada

Patterns of genetic variation among Brachionus plicatilis clones collected at different times from Soda Lake, Nevada (U.S.A.) were determined using polyacrylamide gel electrophoresis of isozymes. Six of the eleven enzymes assayed were variable. Three of these — malic dehydrogenase (MDH), cholinesterase (CHO), and phosphoglucomutase (PMG) - were selected to screen the 138 clones established from the field collections. Each enzyme revealed variation both within and between field samples. Thirty-eight of the 100 potential composite electromorphs formed by combining isozyme variants were found in the 138 clones. A substantial amount of genetic variation is therefore present. Patterns of electromorph frequency change resembled those reported for cladocerans. No evidence was found for a seasonal succession of distinct electromorphs. We suggest that the B. plicatilis in Soda Lake constitute a single population.     

A brief evolutionary excursion comes to an end: the genetic relationship of British species of Gentianella sect. Gentianella (Gentianaceae)

 There is much taxonomic confusion in the genus Gentianella section Gentianella, five species of which are found in Britain. Gentianella anglica is a British endemic restricted in its distribution to the chalk downland of southern England. It is considered to be threatened because of habitat loss, and due to hybridisation with the closely related, widely distributed G. amarella. The Red Data Book species, G. uliginosa, shares morphological similarities with the other two species but has a very restricted distribution. Individual plants from populations across the range of these three species were analysed using AFLPs and universal cpSSRs to determine the degree of genetic variability within and between them, and to look for evidence of hybridisation. Samples of the two other Gentianella section Gentianella species found in Britain, G. campestris and G. germanica, were also included in the study. The analysis of chloroplast SSRs was not informative for G. anglica, G. amarella and G. uliginosa, while G. campestris and G. germanica differed from each other and the other three species at a single locus. Principal co-ordinate analysis of the AFLP data revealed only three distinct groups: one group contained G. campestris samples, another contained all samples of G. germanica, and a third contained all individuals from the other three species. In mixed populations of G. anglica and G. amarella, individuals of the two species were genetically more similar to each other than they were to individuals of the same species from other populations. It is proposed that G. anglica may be an early flowering form of G. amarella that has been created and maintained as a consequence of former grassland management practices. Received May 20, 2002; accepted October 28, 2002 Published online: March 31, 2003     

Comparison of five strains of a parthenogenetic species,Macrotrachela quadricornifera (Rotifera,Bdelloidea)

Five clonal populations belonging to the parthenogenetic species Macrotrachela quadricornifera were analyzed electrophoretically. The populations stemmed from samples collected from different environments paired geographically: water bodies (C, P, F) and terrestrial mosses (Ml, M2). The six enzymes considered were: leucine amino peptidase (LAP), arginine phosphokinase (APK), glucose phosphate isomerase (PGI), and esterases (EST) and malic enzyme (ME). The results are interpreted under the assumption that bdelloid rotifers have a diploid chromosome set. A genetic interpretation of the banding patterns was attempted. A relatively high degree of enzymatic polymorphism among the strains was found. Only 27% of alleles are shared by all strains. The relationship among the strains was examined by single-link cluster analysis: we can distinguish moss and water populations, regardless of their geographic origins, and in accord with the results of a life-history traits study on the same strains. The differences in life-history parameters among the five strains may be due not only to phenotypic plasticity induced by the environment, but to real genetic divergence.     

Microsatellite DNA variation in Bornean orangutans (Pongo pygmaeus)

Orangutans (Pongo pygmaeus) on the islands of Borneo and Sumatra are considered two separate subspecies. However, the genetic relationships between isolated populations on Borneo are not clear. This study determined the extent of variation within the Bornean subspecies of orangutan, using microsatellite DNA analysis. Blood samples were collected from 96 individuals of known origin from East, West and Central Kalimantan. Human microsatellite primer pairs located at human map position D2S141, D4S431, D 11S925, D16S420 and D17S791 were suitable for use in primates. D4S431 appeared monomorphic for all orangutans. In three cases (D2S141 East and West and D16S420 West), a highly significant excess of homozygous allele frequencies was detected, but with other primer pairs no significant difference in allele frequencies occurred. We conclude that the divergence between the different populations on Borneo is less than the variation within the populations. There was also evidence that inbreeding occurred within the populations.     

High levels of genetic variation in natural populations of marine lower invertebrates

The predictions of neutralist and selectionist hypotheses have been tested many times in the past, but mostly using data only from organisms such as vertebrates, with generally low to average heterozygosities. The more recent discovery of particularly high levels of genetic variation in marine sponges and coelenterates provides an opportunity to use data from such species to contribute further to the understanding of the determinants of heterozygosity in natural populations. Therefore, 23 species of sponges and coelenterates from temperate, tropical and boreal waters were analysed by gel electrophoresis for an average of 14.3 enzyme loci per species. Mean heterozygosity values for each species were unusually high, ranging between 0.106 and 0.401. The means and variances of the heterozygosity estimates showed reasonable correlation with neutralist predictions (with both the stepwise mutation and the infinite alleles models). Population sizes were generally difficult to estimate with any confidence, but, for one sponge species for which this was possible, levels of heterozygosity again were similar to neutralist predictions, although the same was not apparently true for three species of sea anemone. No differences were found between heterozygosity levels of tropical and temperate species of sponges and coelenterates, thus apparently contradicting the selectionist ‘trophic resource stability’ and ‘temporal environmental variation’ hypotheses. Conversely, however, the consistently high levels of genetic variation found in coelenterates and sponges may be argued to be related to common biological characteristics, such as sessile life, great evolutionary ‘age’, limited ability to disperse and probable low homoeostatic capability. Our results seem, overall, to agree well with neutralist expectations for species with large, stable population sizes. Also, the mean heterozygosities, their variances and the observed and expected proportions of polymorphic loci seem to fit well with predictions based on the neutralist hypothesis. However, the selectionist ‘environmental grain’ and the ‘shifting balance’ hypotheses fit the data equally well. As with much earlier work, the problems in distinguishing between the various predictions of selectionist or neutralist ideas make it both difficult and unwise to draw definite conclusions.     

INTRASPECIFIC VARIATION IN THE DINOFLAGELLATE PERIDINIUM VOLZIP1

Clonal isolates of Peridinium volzii Lemmerman were analyzed morphologically and biochemically. Morphological observations at the light microscope level show the clones to be different varieties and forms of the same species. Biochemical analysis by enzyme electrophoresis and flow cytometric determination of nuclear DNA quantities indicates that these isolates are genetically heterogeneous without any clear correlation existing between morphological variation and biochemical variation. Isozyme analysis, however, indicates that strains from the same location are generally more related to each other than they are to isolates with other geographical origins. In general, our results suggest the presence of genetic redundancy and a multiclonal origin for individuals of the same species present in the same locale.     

Isozyme Variability in Plants Regenerated from Calli of Cereus peruvianus (Cactaceae)

Morphological and isozyme variation was observed among plants regenerated from callus cultures of Cereus peruvianus. Different morphological types of shoots (68%) were observed in 4-year-old regenerated plants, while no distinct morphological variants were observed in plants grown from germinated seeds. Isozyme patterns of 633 plants regenerated from calli and of 261 plants grown from germinated seeds showed no variation in isocitrate dehydrogenase isozyme, and the differential sorbitol dehydrogenase, alcohol dehydrogenase, malate dehydrogenase, acid phosphatase, and peroxidase isozyme patterns observed in regenerated plants were attributed to nonallelic variation. Allelic variation was detected at three isoesterase loci. The proportion of polymorphic loci for both populations was 13.6% and the deviation from Hardy–Weinberg equilibrium for the Est-1 and Est-7 loci observed in somaclones was attributed to the manner in which the regenerant population was established. The high values for genetic identity among regenerant and seed-grown plant populations are in accordance with the low levels of interpopulation genetic divergence. In somaclones of C. peruvianus, morphological divergence was achieved within a short time but was not associated with any isozyme changes and also was not accompanied by biochemical genetic divergence.     

The evolution of Spartina anglica C.E. Hubbard (Gramineae): origin and genetic variability

An extensive survey of isozyme phenotypes in British populations of the amphidiploid salt marsh grass Spartina anglica and its putative parents has confirmed that the species arose by chromosome doubling in S. × townsendii , a sterile hybrid between S. maritima and S. alterniflora. Isozyme phenotypes and seed protein profiles indicate that S. anglica is almost totally lacking in genetic variation. Isozyme evidence also indicates that the parental species are characterized by low levels of genetic variation. The lack of variation in S. anglica is proposed as being due to a narrow genetic base resulting from a single origin, or a multiple origin from uniform parents; the fact that many populations are derived from very small founder populations; and because preferential pairing between identical homologous chromosomes prevents recombination between the divergent component genomes of the species. The low levels of isozyme variation that occur appear to be due to chromosome loss.
The consequences for the future evolution of S. anglica , given its lack of genetic variation, are discussed.     

厚壳桂新微卫星体分子标记的开发与应用(英文)

生境破碎化是导致全球生物多样性危机的主要原因,即使常见物种也会受到很大影响.厚壳桂(Cryptocarya chinensis)是我国南亚热带季风常绿阔叶林群落演替顶极物种,由于这一森林植被的破坏而呈片断化分布.在以往的研究中,我们利用筛选到的一些微卫星体对其遗传多样性研究后发现其可能以无性生殖为主.为进一步证实这一发...     

Determining Management Units in Southeastern Brazil: The Case of Astyanax bimaculatus (Linnaeus, 1758) (Teleostei: Ostariophysi: Characidae)

Characterization, management and protection of biodiversity are the most prominent challenges in conservation biology. Analyses on molecular similarity (Random Amplified Polymorphic DNA-Polymerase Chain Reaction, RAPD-PCR) and morphologic patterns (morphometric and meristic characters) were performed to evaluate the existence of population structuring in the Doce river basin, in a widespread small-sized characin, Astyanax bimaculatus. Three hundred (300) individuals were collected from six locations isolated by waterfalls or dams, in the Doce river basin, Minas Gerais State, Brazil. Genetic differentiation among tributaries was significant (p<0.00001) and accounted for 21% of total variance (p<0.00001). Only the Grande waterfall of the Casca river was an effective factor for differentiation of populations (p<0.00001), and meristic characters were also consistent with molecular data. We concluded that genetic and morphologic variation of this species was not necessarily associated with waterfalls and that molecular and meristic data are effective predictors of population divergence in this basin. The consequences of these findings for the protection and management of aquatic biodiversity were discussed.     

COST OF REPRODUCTION IN POLEMONIUM VISCOSUM: PHENOTYPIC AND GENETIC APPROACHES

I measured the effect of early reproduction on subsequent growth and survival in the alpine perennial wildflower, Polemonium viscosum. Measurements were made over 4 yr on 34 maternal sibships under natural conditions. A significant phenotypic cost of early reproduction characterized the study population. Plants that flowered after only one year's growth had twice as many leaves and 25% more shoots than nonflowering individuals of equal age. However, early flowering decreased leaf number by 18% in the subsequent year and survivorship by 20% after two years relative to changes in leaf number and survival of nonflowering plants. For such trade-offs to shape the further evolution of reproductive schedules, flowering probability and those age-specific components of plant size that represent the energetic currency for reproductive costs must be heritable. Although families showed significant heterogeneity in the probability of early flowering, most (62%) entirely failed to flower. Moreover, phenotypic variation in vegetative size components at ages 1 and 2 had little genetic basis. Only at ages 3 and 4, after vegetative and demographic costs of early reproduction had been incurred, did vegetative size components (leaf length and number, and shoot number) vary significantly among families. Results of this study provide little evidence of a genetically based trade-off between early reproduction and subsequent survival in P. viscosum.