Polymorphic inversion and esterase loci complex on chromosome 2 of Drosophila buzzatii. II. Spatial variation

The potential influence of linked inversions on allele frequency variation at the Est-1 and Est-2 loci among Australian populations of D. buzzatii was determined by statistical analyses allele and inversion gametic frequencies. Most of the significant spatial and climatic associations found for all Est-1 allele frequencies, and for one allele only of Est-2 (Est-2c+), were accounted for by their linkage disequilibria with the inversions, which covaried with environmental variables. Consistent with this result, the spatial and climatic associations for conditional Est-1 and Est-2 allele frequencies tended to be different from those for the respective unadjusted allele frequencies. In one important respect, the results for Est-1 and Est-2 were not altered by inversions. For both unadjusted and conditional Est-1 allele frequencies, few climatic associations remain after correcting for geographic location, whereas for both unadjusted and conditional Est-2 allele frequencies, climatic associations remain after correcting for geographic location. Thus, apparent selection affecting allele frequencies at the Est-2 locus is not accounted for by linked inversions.     

Change in the genetic structure of an experimental population of Drosophila by electrophoretic locus under the effect of ecological conditions]

Dynamics of the genetic structure of experimental Drosophila populations being kept over 50 generations at 25 and 17 degrees C6 and on the medium with ethanol (12%) was studied. In all experimental populations alteration in allele frequencies of Adh, Gpdh, Hex and Est-6 loci took place in the first 20-25 generations on monitoring under the influence of the temperature and ethanol. Later on, an equilibrium relation between allele frequencies will be established.     

Apparent Selection of Enzyme Alleles in Laboratory Populations of Drosophila

Twelve laboratory populations of recently collected Drosophila willistoni were begun with different frequencies of alleles at three enzyme loci, six populations at 25 degrees and six at 19 degrees . Periodic sampling of the populations allowed monitoring of the frequency changes in allozymes over time.-At Lap-5 (a locus coding for leucine amino peptidase), three alleles converged to the same frequencies in all populations at both temperatures. The apparent equilibrium frequency of the major allele was about.75; this is different from the frequency (.57) found in the natural population from which the experimental populations were begun. Allele frequency changes at the esterase-5 locus (Est-5) were slower but consistent in all cages. It is difficult to determine if an equilibrium has been reached. However, the frequency of the rare allele in all cages is about the same as in wild populations, 5%. Alleles at both Lap-5 and Est-5 are non-randomly associated with inversions in the chromosomes onto which they map. Because of these associations, it is impossible to unambiguously attribute the change in allele frequencies to selection at the loci being observed.-After one year, no significant gene frequency changes were detected at Est-7, the third locus studied.     

Spatiotemporal allozyme divergence caused by aridity stress in a natural population of wild wheat, Triticum dicoccoides, at the Ammiad microsite, Israel

Spatiotemporal diversity at 35 allozyme loci was assayed over 6 years in 1,207 individuals of wild emmer wheat (Triticum dicoccoides)from a microgeographic microsite, Ammiad, north Israel. This analysis used new methods and two additional sample sets (1988 and 1993) and previous allozymic data (1984–1987). This microsite includes four major habitats (North-facing slope, Valley, Ridge, and Karst) that show topographic and ecological heterogeneity. Significant temporal and spatial variations in allele frequencies and levels of genetic diversity were detected in the four subpopulations. Significant associations were observed among allele frequencies and gene diversities at different loci, indicating that many allele frequencies change over time in the same or opposite directions. Multiple regression analysis showed that variation in soil-water content and rainfall distribution in the growing season significantly affected 10 allele frequencies, numbers of alleles at 8 loci, and gene diversity at 4 loci. Random genetic drift and hitchhiking models may not explain such locus-specific spatiotemporal divergence and strong allelic correlation or locus correlation as well as the functional importance of allozymes. Natural ecological selection, presumably through water stress, might be an important force adaptively directing spatiotemporal allozyme diversity and divergence in wild emmer wheat at the Ammiad microsite. Received: 3 July 2000 / Accepted: 1August 2000     

Gametic associations between inversion and allozyme polymorphisms in Drosophila buzzatii.

Gametic disequilibria between second chromosome polymorphic arrangements and seven linked allozyme loci were estimated in seven populations of Drosophila buzzatii from Argentina. Significant and consistent associations across populations were detected for Est-1, Est-2, Aldox, and XDH: Phenograms based on Nei's genetic distance showed that chromosomes carrying the 2ST arrangement were more similar to each other, irrespective of the population from which they were extracted, than to chromosomes carrying the derived 2J and 2JZ3.Restriction of recombination in heterokaryotypes seems to be the best explanation for the significant linkage disequilibria between inversions and the loci located inside the rearranged segments, for example, Est-1 and Aldox, or close to the break points, for example, Est-2. However, epistatic interactions between Xdh, which is outside the inversions and not near the break points, and loci tightly linked to the inversions, is the most likely explanation for the association between Xdh and chromosomal arrangements. Some of the associations detected in endemic Argentinean populations are coincident with data obtained in colonizing populations of the Old World and Australia. Thus historical processes that took place in the original area of the species' distribution can account for these linkage disequilibria in colonized populations of D. buzzatii.     

Polymorphism and inheritance of serum esterases and beta-globulins in the paradise fish (Macropodus opercularis; Anabantidae)

Electrophoretic variants of serum esterases and beta-globulins in two subspecies of paradise fish (Macropodus opercularis) were studied. Four esterase loci (Est-1, Est-2, Est-3 and Est-4), a single transferrin (Tf) and another major beta-globulin locus (Bg) were identified by segregational analysis. Est-3 seems to be a monomorphic locus. Three alleles of Est-1, two of Est-2, two of Est-4, four of Tf and two alleles of Bg were found in the laboratory population. None of these loci were closely linked. Electrophoretic patterns of F1 hybrids confirmed the monomeric structures of each of the studied proteins. Allelic segregation at the Tf and Bg loci was normal in F2 and backcross populations. In crosses of the two Macropodus subspecies there were deviations from Mendelian ratios because of missing recombinant esterase phenotypes. Each of these would have been homozygous Est-2f/f. We suppose that Est-2f/f causes lethality in the early phase of development, except in the Est-1c/c, Est-2f/f combination characteristic of the parental subspecies M.o. concolor.     

Temporal variation of allele frequencies in populations of Akodon dolores (Rodentia,Cricetidae)

Summary Six population samples of the South American cricetid rodent Akodon dolores were collected at the same site at six-month intervals over a three year period. Changes in density were detected. Seven out of 18 loci analyzed by means of starch gel electrophoresis were polymorphic. Only two of these loci (Est-4 and G6pdh) showed statistically significant variation in allele frequencies following a seasonal pattern. There was no correlation between allele frequencies and population density. When animals were grouped into two classes according to body weight, a clear difference in allele distribution at the Est-4 and G6pdh loci was observed between individuals 39 g or less and those heavier than 39 g. As the first group comprises predominantly younger animals, the data indicate that changes in the age-structure of population, rather than density variations, are responsible for the cyclic pattern of allele frequencies fluctuations.     

Influence of defined gene blocks on the competitive ability of yeast genotypes

Competition experiments were carried out under varying exogenic and endogenic conditions. The genotypes were marked by combinations of two esterase loci, each with two alleles. When genotypes of the line W7 were used, there was no demonstrable influence of the gene blocks marked by the Est-1 locus on the competitive ability at temperatures of 21 and 29 C. However, genotypes carrying the fast allele of the Est-2 locus were favored. At 38 C, the outcome of the competition was reversed. The defined gene blocks showed different effects when interacting with different genetic backgrounds (line M7). Genotypes marked by the slow allele of the Est-2 locus were now favored (21 and 29 C), and even the gene blocks marked by the alleles of the Est-1 locus influenced the genotypes' competitive abilities. Again, the results were partly reversed at 38 C. The results are discussed with regard to the importance of enzyme variants for the genotypic selection value.     

Effects of selection for resistance to organophosphorus insecticides on two esterase loci in Drosophila melanogaster

Two laboratory populations of Drosophila melanogaster were exposed to the insecticides ethyl-parathion and fenthion respectively. Three parameters were studied in each generation: resistance to the insecticide (LC 50), AChE activity, and allele frequencies at the Est-6 locus. In both treated populations a significant increase in the resistance was observed within a few generations. This rise in the resistance levels was accompanied by parallel changes in the two esterases AChE and Est-6. With AChE the enzyme activity became considerably higher indicating either structural modification of the enzyme molecule or mutations in the regulatory system of the AChE gene locus. At the Est-6 locus the S allele was eliminated during the selection process which might be due to greater sensitivity of the Est-6^S allozyme.     

Characterization of genetic diversity in core collection accessions of wild barley,Hordeum vulgare ssp. spontaneum

Genetic variability in the 143 core accessions of wild barley, Hordeum vulgare ssp. spontaneum, was assessed by allozyme analysis. A total of 34 alleles were detected at ten isozyme loci. All loci were polymorphic except Pgd-1, which was monomorphic. Est-2 and Est-4 were the most diverse loci, with genetic diversity values of 0.747 and 0.686, respectively. The comparison of the results with those of previous studies indicates that all alleles occurring in cultivated and wild barley are observed in this set of the wild Barley Core Collection. Only one allele (Pgd-1 Tj) was absent. It is noteworthy that one new allele at the Ndh-2 locus and another new allele at Aco-2 locus were first detected in the present study. Nine of the 34 alleles were rare and detected only in one to four accessions. The genetic similarities among the 143 accessions ranged from 0.18 to 1.00. Data analysis based on clustering and principal coordinate analysis showed that a high level of genetic variability exists in this set of core accessions, and indicated that some duplication probably exists in this set core based on the present study.     

Temporal variation of allele frequencies in a natural population of wild Vigna unguiculata

Abstract

Temporal variation in allele frequencies in a natural population of wild Vigna unguiculata was studied by making monthly collections of seeds over a two-year period. Using starch gel electrophoresis, four out of seven loci analysed were shown to be polymorphic (Enp, Fdh, Fle₃ and Pgd₂ ). These four loci showed significant variation in allele frequencies over time. Changes in population structure over time were analysed using F-statistic estimators. Although heterogeneity was evident between loci, the analysis showed significant differentiation among months within a year for all polymorphic loci. Fixation indexes were all positive and statistically different from zero, highlighting a significant departure from random mating. Using analysis of variance (ANOVA), the pattern of inbreeding (f) showed significant changes over time (season); among the polymorphic loci, Enp most strongly contributed to this significance. Significant correlations were found between allele frequencies at different loci. The monthly average gene diversity (He) and allele frequencies at the Enp locus were found to be significantly correlated with weather conditions (temperature and rainfall distribution). These allele frequency deviations over time can be attributed to changes in pollinator behaviour, and frequent genetic bottlenecks that are associated with changes in environmental conditions.     

Age-dependent allozymic variation in a natural population of lizards

An analysis of allozymic variation at 17 loci in a population of the sagebrush lizard (Sceloporus graciosus) in southern Utah yielded an estimate of genic heterozygosity of 0.028. Seven of the loci were variable, but only one, Est-1, was strongly polymorphic. The observation that the frequency of the common genotype (MM) at the Est-1 locus declined monotonically in successive age classes from 0.74 in hatchlings to 0.58 in adults 4 years old or older suggests that allele frequencies at this locus are not independent of selective influences.This research was supported by NSF grant GB-29141 to D.W.T. and NIH grant GM-15769 to R.K.S.     

Population genetic structure of Nantucket pine tip moth

Summary Variation at polymorphic isozyme loci was analyzed in Nantucket pine tip moth (NPTM) populations from 5 geographic locations. At the North Carolina location, populations representing 3 generations at 3 local sites were also studied. Four of the loci investigated (LAP, MDH, -GPDH and AK), although variable, had few alleles per locus (3–5) and few differences among populations in allele frequencies. At each locus, all populations had the same allele at a high frequency.At the PGM locus, fifteen alleles were identified and allelic frequencies varied among populations. At least eight alleles were present within a population and, in most populations, two or more alleles had high frequencies that differed among populations. An excess of homozygotes over Hardy-Weinberg expectations was found for 7 out of the 10 populations studied, indicating the probable existence of some form of inbreeding structure or populational subdivision within sampled stands.Joint consideration of the results observed for PGM and the other four loci is counterindicative of neutrality at all loci and strongly indicative of genetic differentiation among locally disjunct populations.Published as Paper No. 6751 of the Journal Series of the North Carolina Agricultural Research Service     

Genetic divergence between populations of two closely related troglobitic beetle species (Speonomus: Bathysciinae,Coleoptera)

Genetic variability and divergence at 13 enzyme loci were studied in two species of troglobitic beetles (Speonomus zophosinus andhydrophilus 12 populations) collected from the Pyrenees mountains. These allopatric species exhibit a high degree of specialization to underground life and a very small geographical range. Four diagnostic loci arePgi, Est-2, Pac-1, Phi. Within each species polymorphic loci exhibited marked spatial variation of allele frequencies, sometimes over short distances (5–10 km). The levels of genetic variability are comparable to those observed in non-cave invertebrates (frequency of polymorphic loci: 0.31; average expected heterozygosity: 0.112±0.015). Moreover, a single species showed variability in the average level of heterozygosity (0.06 to 0.172). Patterns of genetic differentiation among species were also studied; mean genetic distance (D: 0.263±0.010) between the twoSpeonomus species was of the same order of magnitude as most data reported in the literature between species. A significant heterozygote deficiency occurs in local populations and for all loci. This deficit does not vary from locus to locus. Several hypotheses were examined in an attempt to account for these observations in connection with the species biology. This deficit probably is due to the breeding structure of the population (inbreeding and assortative mating) coupled with limited dispersal ability.     

Microgeographic genetic variation in the apple maggot rhagoletis pomonella

We examined electrophoretic variability at five enzyme loci in the apple maggot fly, Rhagoletis pomonella, on a microgeographic scale. Treating flies from individual hawthorn trees as separate populations, we estimated F(ST) values from allele frequencies. The results indicate that there is significant allele frequency heterogeneity among fly populations over a small spatial scale at some loci but not at others. This variation among loci in degree of differentiation is itself statistically significant, casting doubt on the role of genetic drift in maintaining the heterogeneity. There is also heterogeneity between years in flies from a given tree. These data provide a baseline with which future work on genetic differentiation among apple maggot populations associated with different species of host plants may be compared.     

Associations of Alleles of the Esterase-1 Locus with Gene Arrangements of the Left Arm of the Second Chromosome in DROSOPHILA ROBUSTA

Evidence of strong associations of Est-1 alleles with the 2L, 2L1 and 2L3 gene arrangements of the left arm of the second chromosome in D. robusta is presented. Each gene arrangement is polymorphic for three to four Est-1 alleles. The allele frequencies differ in the 2L3 and 2L arrangements; the allele Est-1^.92 is 8% in the 2L3 arrangement (n=203)—this allele is 82% in the 2L arrangement (n=203); the allele Est-1^1.0 is 66% and 14.8% in the 2L3 and 2L arrangements, respectively. There are no differences in allele frequencies in 2L3 arrangements from any of the widely separated seven different populations; similarly the allele frequencies in the 2L arrangement are alike in all five widely separated populations studied. The allele frequencies in the 2L1 arrangement are intermediate to those observed in the 2L3 and the 2L arrangements and show north-south clinal change. These associations between Est-1 alleles and gene arrangements of the left arm of the second chromosome are due to natural selection favoring different allele frequencies in different gene arrangements, as a result of epistatic interactions between the Est-1 locus and the loci on the gene arrangements. As expected, we observe that the proportion of heterozygotes is greater in the inversion heterokaryotypes than in the homokaryotypes.     

Patterns of Gene Variation in Central and Marginal Populations of DROSOPHILA ROBUSTA

The central and marginal populations of D. robusta differ greatly in the level of inversion polymorphism; the marginal populations are monomorphic or nearly so and the central populations are highly polymorphic. This paper presents the frequencies of alleles at forty gene loci in various populations of D. robusta, studied by electrophoresis of proteins and enzymes. Population samples were obtained from eight widely separated populations of D. robusta which included the central, the extreme marginal and the intervening populations between the center and the margins. We find that the proportion of polymorphic loci and average heterozygosity per individual is slightly higher in the marginal populations than the central populations. In D. robusta on an average, 39% of the loci are polymorphic and the average proportion of loci heterozygous per individual is 11%. A breakdown of loci in three categories, viz, hydrolytic enzymes and some other enzymes, larval proteins and glycolytic and Kreb's cycle enzymes, shows that in all populations the level of polymorphism is highest in the hydrolytic enzymes, intermediate in larval proteins and least in the glycolytic and Kreb's cycle enzymes. On the average, the proportion of loci heterozygous per individual for three groups of loci is: hydrolytic enzymes and others (.164), larval proteins (.115) and glycolytic and Kreb's cycle enzymes (.037). We also observe that in all populations the level of polymorphism on the X chromosome is far less than the expected 38%; in salivary gland cells the euchromatic length of the X chromosome is 38% of the entire genome. Lower levels of polymorphism for the X chromosome loci are explained due to low probability of balanced polymorphisms for the X-linked loci since the conditions for establishment of balanced polymorphism for X-linked loci are more restrictive than for the autosomal loci.-The polymorphic loci can be grouped according to pattern of allele frequencies in different populations as follows: (1) The allele frequencies are similar in all populations at the XDH, Pep-1 and Hex-1 loci. (2) The alleles at the Est-1, Est-2, Amy loci and the AP-4(1.0) and the LAP-1(.90) alleles show north south clinal change in frequency. (3) There is north south and east west differentiation at the Pt-5, Pt-8 and Pt-9 loci and the allele AP-4(.81). (4) Polymorphism at loci such as Fum, B.Ox, Hex-8, Pep-2 and Pep-3 are restricted to only one or two of the populations. (5) Allele frequencies at the MDH and ODH loci fluctuate between populations. (6) Allele frequencies at many polymorphic loci such as Est-1, Est-2, LAP-1, AP-4, Pt-5, Pt-8, Pt-9, Pt-16, MDH, Fum change clinally within a gene arrangement. The pattern of gene variation in D. robusta is very complex and cannot be easily explained due to migration of neutral alleles between once-isolated populations or to semi-isolation of neutral alleles. The observations of the pattern of allele variation in different populations, high levels of polymorphism in the marginal populations which have small population size and low levels of polymorphism of the X chromosome loci all support the argument in favor of balancing selection as the main mechanism for the maintenance of these polymorphisms. Environmental factors must play a role in the maintenance of a great deal of these polymorphisms, since we observe clinal allele frequency changes even within a given inversion type.     

Serum esterase genetics in rabbits. IV. The prealbumin and β-globulin systems

Discontinuous starch gel electrophoresis revealed a fourth allele of rabbit prealbumin serum esterase at locus Est-2. This allele is designated Est-2 ^f and appears to be silent. In addition to the prealbumin serum esterases, another serum esterase system was studied in rabbits. This system is localized in the β-globulin region. Genetic analysis indicated that one locus with two codominant alleles controls the variation in this region. Linkage of this system with Est-1 and Est-2 of the prealbumin serum esterases was demonstrated. Comparison of the arrangement of these esterase loci on linkage group VI with the esterase loci on chromosome 8 of the mouse gives additional support for the theory of evolutionary conservation of chromosomal segments coding for mammalian esterases.     

Allozyme Diversity among Different Size Cohorts of Spat of Mytilus trossulus (Bivalvia,Mytilidae) Dwelling together in Amursky Bay,Sea of Japan

Allozyme variability in 16 polymorphic loci in two size cohorts of large (30.0 ± 6.3 mm) and small (9.8 ± 2.3 mm) spat of the mussel Mytilus trossulus (Gould) coinhabiting the intertidal zone in Brazhnikov Bay (Amursky Bay, Sea of Japan) was studied 1988–1989. It was determined that the size cohorts compared were highly similar genetically; Nei's minimum distances were 0.014 and 0.016 in 1988 and in 1989. However, statistically significant differences in allele frequencies were found at 2 loci, both in 1988 and in 1989. The loci differing by allele frequencies in 1988 did not coincide with those in 1989. Significant differences by heterozygosity between the cohorts were found only at the Idg-1 and Est-3 loci, 1988; and at the Aat-1, 6-Fgd, Est-3 loci, 1989; but the average heterozygosity was not significantly different in the cohorts for both years. A deficiency of heterozygotes (Dg) was observed almost at all loci in both cohorts. The mean Dg values were significantly higher in the cohort of small size individuals. Since the environmental conditions for both cohorts were similar, the allozyme differences between them were not a result of natural selection. A possible cause of the allozyme and size differences among the mussel cohorts is the gap in the settling time of larvae, which entails the formation of two size cohorts of mussels. Such a gap was caused by protraction of spawning period of M. trossulus and by the formation of segregate larval pools from various mussel populations differing in allele frequencies.     

An esterase duplication in Drosophila: Differences in expression of duplicate loci within and among related species

An esterase duplication is described in the sibling species pair Drosophila mojavensis and Drosophila arizonensis. We present evidence for two separate structural loci mapping at a distance of less than 0.16 recombination units from each other. Alleles at the two loci have the same substrate specificities and form small amounts of interlocus heterodimers. One locus (Est-5) is functioning throughout the insect's life cycle and appears at high concentrations in the hemolymph and the fat body. Its duplicate (Est-4) functions only during the late larval stage and is concentrated mainly in the carcass. No null alleles at either locus were observed in population surveys. An examination of 12 other species from the repleta group, to which D. mojavensis and D. arizonesis belong, suggests that Est-5 is universally present, but the activity levels of Est-4 vary among species and may be totally absent in some species. Variation in the level of Est-4 activity does not closely follow the phylogenetic relationship.