Elucidation of the genetic differences in Trialeurodes vaporariorum populations under vegetable greenhouse conditions by using the allozyme approach

Genetic differentiation of Trialeurodes vaporariorum (Westwood 1856) populations was examined using biochemical and allozyme analysis. For biochemical analysis, general esterase and glutathion‐S‐transferase were tested. Allozyme genetic variability in 11 populations of T. vaporariorum was investigated using five loci from four enzyme systems. Although there are large variations between populations, T. vaporariorum is grouped into two populations with geographic barriers, based on Nei's genetic distance in the Baekdudaegan Mountains. Within these two groups, low migration and linkage disequilibrium reveal that populations tend to be influenced by gene drift rather than uniform selection pressures. The effect of genetic drift is greater than the effect of uniform selection by insecticides or host plant resistance, which is suggested by the F_ST estimates in this study. Based on this basic research, more effective whitefly control programs could be built in the future.     

Analysis of F ST outliers at allozyme loci in Pacific salmon: implications for natural selection

Natural selection has been invoked to explain the observed geographic distribution of allozyme allele frequencies for a number of teleost species. The effects of selection on allozyme loci in three species of Pacific salmon were tested. A simulation-based approach to estimate the null distribution of population differentiation (F _ST) and test for F _ST outliers was used. This approach showed that a majority of allozyme loci conform to neutral expectations predicted by the simulation model, with relatively few F _ST outliers found. No consistent F _ST outlier loci were found across species. Analysis of population sub-groups based on geography and genetic identity reduced the number of outlier loci for some species, indicating that large geographic groups may include genetically divergent populations and/or that there is geographic heterogeneity in selection pressure upon allozyme loci. Two outlier allozyme loci found in this analysis, lactate dehydrogenase-B and malic enzyme, have been shown to be influenced by selection in other teleost species. This approach is also useful in identifying allozyme loci (or other genetic markers) that meet assumptions for population genetic study.     

Microsatellite polymorphism and genetic differentiation in three Norwegian populations of Elymus alaskanus (Poaceae)

 Variation at seven microsatellite loci was investigated in three local E. alaskanus populations from Norway and microsatellite variation was compared with allozyme variation. The percentage of polymorphic loci was 81%, the mean number of alleles per polymorphic locus was 5.7 and expected heterozygosity was 0.37. An F-statistic analysis revealed an overall 48% deficit of heterozygotes over Hardy-Weinberg expectations. Gene diversity is mainly explained by the within population component. The averaged between population differentiation coefficient, F _st , over 7 loci is only 0.13, which accounts for only 13% of the whole diversity and was contrary to allozyme analysis. The mean genetic distance between populations was 0.12. However, a χ² -test showed that allele frequencies were different (p < 0.05) among the populations at 5 of the 7 loci. In comparison with the genetic variation detected by allozymes, microsatellite loci showed higher levels of genetic variation. Microsatellite analysis revealed that population H10576 possesses the lowest genetic variation among the tested three populations, which concur with allozyme analysis. The dendrogram generated by microsatellites agreed very well with allozymic data. Our results suggest that natural selection may be an important factor in shaping the genetic diversity in these three local E. alaskanus populations. Possible explanations for deficit heterozygosity and incongruence between microsatellites and allozymes are discussed. Received November 6, 2001; accepted April 24, 2002 Published online: November 14, 2002 Addresses of the authors: Genlou Sun (e-mail: Genlou.sun@STMARYS.CA), Biology Department, Saint Mary's University, Halifax. Nova Scotia, B3H 3C3, Canada. B. Salomon, R. von Bothmer, Department of Crop Science, The Swedish University of Agricultural Sciences, P.O. Box 44, SE-230 53, Alnarp, Sweden.     

Deeply divergent lineages of the widespread New Zealand amphipod Paracalliope fluviatilis revealed using allozyme and mitochondrial DNA analyses

1. We evaluated the population genetic structure of the common New Zealand amphipod Paracalliope fluviatilis using eight allozyme loci, and the mitochondrial cytochrome oxidase c subunit I (COI) gene locus. Morphological analyses were also conducted to evaluate any phenotypic differences. Individuals belonging to P. fluviatilis were collected from a total of 14 freshwater fluvial habitats on the North and South Islands, New Zealand. 2. We found evidence for strong genetic differentiation among locations (Wright's F_ST > 0.25), and fixed differences (non‐shared alleles) at two of the eight allozyme loci indicating the possibility of previously unknown species. Analysis of a 545‐bp fragment of the COI locus was mostly congruent with the allozyme data and revealed the same deeply divergent lineages (sequence divergences up to 26%). 3. Clear genetic breaks were identified between North Island and South Island populations. North Island populations separated by <100 km also showed genetic differences between east and west draining watersheds (sequence divergence >12%). Accordingly, present‐day dispersal among hydrologically isolated habitats appears minimal for this taxon. 4. Although population differences were clearly shown by allozyme and mtDNA analyses, individuals were morphologically indistinguishable. This suggests that, as in North American and European taxa (e.g. Hyalella and Gammarus), morphological conservatism may be prevalent among New Zealand's freshwater amphipods. We conclude that molecular techniques, particularly the COI gene locus, may be powerful tools for resolving species that show no distinctive morphological differences.     

Patterns of allozyme variation in relation to population size of the threatened plantMegaleranthis saniculifolia (Ranunculaceae) in Korea

Patterns of variation at 27 allozyme loci were investigated in the endangered endemic plantMegaleranthis saniculifolia. Levels of allozyme variation (A = 1.47,P = 40%,He = 0.088) were also compared with other endemic plant species. Genetic divergence between populations was very high (G ^st = 0.271 ), with moderate to high interpopulation differentiation, which probably arose through historical bottlenecks in a landscape of habitat fragmentation and/or human influence. The percentage of polymorphic loci, heterozygosity, and mean number of alleles per locus were positively related to population size, probably due to the stochastic loss of rare alleles in the smaller populations. Individuals in the small and marginal populations (TB, KD, and CJ) showed higher proportions of fixed loci. These ecologically marginal populations were typically more distant from the nearest neighboring population and were more genetically distinct from one another. The genetic structure of the current population ofM. saniculifolia is probably the result of local extinctions of intervening populations. This, in turn, is due to the Pleistocene climatic change and increased habitat destruction. A positive association appears to exist between genetic diversity and population size. Although these small population sizes are more sensitive to stochastic events, securing a certain number of individuals from the three larger populations (SB, JB, and TG) could be accomplished as part of a conservation strategy. In addition, it is important to prioritize populations in different regions in order to limit population declines caused by large-scale environmental catastrophes.     

Evidence for African origins of founders of the asiatic lion species survival plan

The Asiatic lion (Panthera leo persica) exists in the wild as a single relict population of approximately 250 individuals in the protected Gir Forest Sanctuary in western India. In 1981, a species survival plan (SSP) for the Asiatic lion was established by the American Association of Zoological Parks and Aquariums to manage the 200 + descendants of Asiatic lions in captivity in western zoological facilities. This captive population was derived from seven founders. In order to compare the genetic structure of the Gir Forest population with that of the captive SSP population, a genetic survey of 46 electrophoretic allozyme systems resolved from extracts of lion blood was undertaken by using 29 SSP Asiatic lions and 28 wild-caught or captive-bred lions maintained at the Sakkarbaug Zoo in India but originally derived from the Gir Forest. The Gir lion population was found to be genetically monomorphic at each of 46 allozyme loci. This was in contrast to several African lion (Panthera leo leo) populations, which show moderate levels of allozyme variation at the same loci. The SSP lion population was polymorphic at three allozyme loci (IDHI, TF, and PTI) for alleles that were previously found only in African lion populations. Pedigree analysis of the genetic transmission of these three biochemical loci demonstrated that two of the five primary founder animals of the SSP Asiatic lion population (a breeding pair originally imported from the Trivandrum Zoo in southern India) were descendants of the African subspecies. Three other founder animals were pure Asian. A retrospective SSP pedigree analysis of two morphologic characters (prominent abdominal fold and pairing of infraorbital foramen) that are partially diagnostic for persica vs leo was consistent with this conclusion as well. The implications for the management of small captive populations of threatened species and of the Asiatic lion SSP population are discussed.     

Allozyme polymorphisms of maize populations from southwestern China

Maize (Zea mays L.) is one of the most-important food crops in southwestern China. The diversity of maize populations from southwestern China has been evaluated on the basis of agronomic and morphological data, but not on marker data. Our objectives were to evaluate the allozyme polymorphism of these populations, and group the populations on the basis of allozyme data. We analyzed 27 maize populations from southwestern China and two populations [BS13(S)C2 and Lancaster] from the USA for genetic variation at 18 allozyme loci. We found a total of 69 alleles at 18 allozyme loci with an average of 3.8 alleles per locus. Compared with inbreds, hybrids, and populations from the U.S. Corn Belt, the 27 Chinese populations had a significantly higher (p<0.01) number of allozyme alleles per locus. Maize populations from southwestern China have accumulated abundant genetic diversity, and might be valuable germplasm for broadening the genetic base of U.S. Corn Belt breeding germplasm. The analyses of allele-frequency distributions and the expected heterozygosity also reflected the differences between the Chinese and the U.S. germplasm. The Chinese populations might be valuable germplasm for complementing U.S. Corn Belt breeding germplasm. The analysis of gene diversity showed that 77% of the allozyme variation resided within populations and 23% between populations. This result suggested that breeders should identify one or a few Chinese populations with the best agronomic performance, and exploit the genetic variation within these selected populations. Cluster analysis classified the 29 populations into four main groups. Groupings based on allozyme data could be useful for classifying the populations into different heterotic groups and, consequently, exploiting them in hybrid breeding. Received: 12 October 2000 / Accepted: 13 March 2001     

Estimation of population structure in coastal Douglas-fir [Pseudotsuga menziesii (Mirb.) Franco var. menziesii] using allozyme and microsatellite markers

Characterizing population structure using neutral markers is an important first step in association genetic studies in order to avoid false associations between phenotypes and genotypes that may arise from non-selective demographic factors. Population structure was studied in a wide sample of ∼1,300 coastal Douglas-fir [Pseudotsuga menziesii (Mirb.) Franco var. menziesii] trees from Washington and Oregon. This sample is being used for association mapping between cold hardiness and phenology phenotypes and single-nucleotide polymorphisms in adaptive-trait candidate genes. All trees were genotyped for 25 allozyme and six simple sequence repeat (SSR) markers using individual megagametophytes. Population structure analysis was done separately for allozyme and SSR markers, as well as for both datasets combined. The parameter of genetic differentiation (θ or F _ST) was standardized to take into account high within-population variation in the SSR loci and to allow comparison with allozyme loci. Genetic distance between populations was positively and significantly correlated with geographic distance, and weak but significant clinal variation was found for a few alleles. Although the STRUCTURE simulation analysis inferred the same number of populations as used in this study and as based on previous analysis of quantitative adaptive trait variation, clustering among populations was not significant. In general, results indicated weak differentiation among populations for both allozyme and SSR loci (θ _s = 0.006–0.059). The lack of pronounced population subdivision in the studied area should facilitate association mapping in this experimental population, but we recommend taking the STRUCTURE analysis and population assignments for individual trees (Q-matrix) into account in association mapping.     

Fin whale MDH‐1 and MPI allozyme variation is not reflected in the corresponding DNA sequences

The appeal of genetic inference methods to assess population genetic structure and guide management efforts is grounded in the correlation between the genetic similarity and gene flow among populations. Effects of such gene flow are typically genomewide; however, some loci may appear as outliers, displaying above or below average genetic divergence relative to the genomewide level. Above average population, genetic divergence may be due to divergent selection as a result of local adaptation. Consequently, substantial efforts have been directed toward such outlying loci in order to identify traits subject to local adaptation. Here, we report the results of an investigation into the molecular basis of the substantial degree of genetic divergence previously reported at allozyme loci among North Atlantic fin whale (Balaenoptera physalus) populations. We sequenced the exons encoding for the two most divergent allozyme loci (MDH‐1 and MPI) and failed to detect any nonsynonymous substitutions. Following extensive error checking and analysis of additional bioinformatic and morphological data, we hypothesize that the observed allozyme polymorphisms may reflect phenotypic plasticity at the cellular level, perhaps as a response to nutritional stress. While such plasticity is intriguing in itself, and of fundamental evolutionary interest, our key finding is that the observed allozyme variation does not appear to be a result of genetic drift, migration, or selection on the MDH‐1 and MPI exons themselves, stressing the importance of interpreting allozyme data with caution. As for North Atlantic fin whale population structure, our findings support the low levels of differentiation found in previous analyses of DNA nucleotide loci.