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A A Hoffmann

Publications and source records attributed to A A Hoffmann.

At least 55 records · Page 3Linked to original sources
PubMed1998

Population dynamics of the Wolbachia infection causing cytoplasmic incompatibility in Drosophila melanogaster.

Field populations of Drosophila melanogaster are often infected with Wolbachia, a vertically transmitted microorganism. Under laboratory conditions the infection causes partial incompatibility in crosses between infected males and uninfected females. Here we examine factors influencing the distribution of the infection in natural populations. We show that the level of incompatibility under field conditions was much weaker than in the laboratory. The infection was not transmitted with complete fidelity under field conditions, while field males did not transmit the infection to uninfected females and Wolbachia did not influence sperm competition. There was no association between field fitness as measured by fluctuating asymmetry and the infection status of adults. Infected field females were smaller than uninfecteds in some collections from a subtropical location, but not in other collections from the same location. Laboratory cage studies showed that the infection did not change in frequency when populations were maintained at a low larval density, but it decreased in frequency at a high larval density. Monitoring of infection frequencies in natural populations indicated stable frequencies in some populations but marked fluctuations in others. Simple models suggest that the infection probably provides a fitness benefit for the host in order to persist in populations. The exact nature of this benefit remains elusive.

Analysis of Variance↗
PubMed1997

Environmental stress and the expression of genetic variation.

We have started to test the effects of environmental extremes on the expression of genetic variation for traits likely to be under selection in natural populations. We have shown that field heritability may be high for stress response traits in contrast to morphological traits, which tend to show lower levels of heritable variation in nature compared with the laboratory. Selection for increased stress resistance can lead to a number of other evolutionary changes, and these may underlie trade-offs between favourable and stressful environments. Temperature extremes can have a marked influence on the heritability of life history traits. Heritabilities for fecundity can be high when parental flies are reared at low temperatures and under field conditions. The expression of genetic variation for development time is somewhat more complex when temperature extremes are considered. Populations at species margins may be ideal for studying the effects of environmental stress on evolution.

Animals↗
PubMed1996

Naturally-occurring Wolbachia infection in Drosophila simulans that does not cause cytoplasmic incompatibility.

Microbes of the genus Wolbachia are transmitted by their hosts via the maternal parent and are responsible for cytoplasmic incompatibility among insect populations. This phenomenon can result in Wolbachia spreading through natural populations as previously demonstrated in Drosophila simulans. Here we describe another Wolbachia infection in D. simulans that does not cause cytoplasmic incompatibility. This is a property of the Wolbachia rather than the nuclear background. The infection occurs at a low frequency in natural populations from eastern Australia. The infection shows perfect maternal transmission in the field and does not cause any detectable deleterious effects on its host. These findings suggest that the Wolbachia infection behaves like a neutral variant in populations. The infection may represent an evolutionary outcome of interactions between Wolbachia infections and their hosts.

Animals↗
PubMed1996

Response of two heat shock genes to selection for knockdown heat resistance in Drosophila melanogaster.

To identify genes involved in stress resistance and heat hardening, replicate lines of Drosophila melanogaster were selected for increased resistance to knockdown by a 39 degrees heat stress. Two selective regimes were used, one with and one without prior hardening. Mean knockdown times were increased from approximately 5 min to > 20 min after 18 generations. Initial realized heritabilities were as high as 10% for lines selected without hardening, and crosses between lines indicated simple additive gene effects for the selected phenotypes. To survey allelic variation and correlated selection responses in two candidate stress genes, hsr-omega and hsp68, we applied denaturing gradient gel electrophoresis to amplified DNA sequences from small regions of these genes. After eight generations of selection, allele frequencies at both loci showed correlated responses for selection following hardening, but not without hardening. The hardening process itself was associated with a hsp68 frequency change in the opposite direction to that associated with selection that followed hardening. These stress loci are closely linked on chromosome III, and the hardening selection established a disequilibrium, suggesting an epistatic effect on resistance. The data indicate that molecular variation in both hsr-omega and.hsp68 contribute to natural heritable variation for hardened heat resistance.

Alcohol Dehydrogenase↗
PubMed1995

Cytoplasmic incompatibility in Drosophila simulans: dynamics and parameter estimates from natural populations.

In Drosophila simulans, cytoplasmically transmitted Wolbachia microbes cause reduced egg hatch when infected males mate with uninfected females. A Wolbachia infection and an associated mtDNA variant have spread northward through California since 1986. PCR assays show that Wolbachia infection is prevalent throughout the continental US and Central and South America, but some lines from Florida and Ecuador that are PCR-positive for Wolbachia do not cause incompatibility. We estimate from natural populations infection frequencies and the transmission and incompatibility parameter values that affect the spread of the infection. On average, infected females from nature produce 3-4% uninfected ova. Infected females with relatively low fidelity of maternal transmission show partial incompatibility with very young infected laboratory males. Nevertheless, crosses between infected flies in nature produce egg-hatch rates indistinguishable from those produced by crosses between uninfected individuals. Incompatible crosses in nature produce hatch rates 30-70% as high as those from compatible crosses. Wild-caught infected and uninfected females are equally fecund in the laboratory. Incompatibility decreases with male age, and age-specific incompatibility levels suggest that males mating in nature may often be 2 or 3 weeks old. Our parameter estimates accurately predict the frequency of Wolbachia infection in California populations.

Africa, Southern↗
PubMed1995

Ecological population genetics: the interface between genes and the environment.

We review recent studies in ecological genetics considering the way genes interact with the environment. Studies on morphological and allozyme polymorphisms continue to highlight problems in identifying selective factors. Selection on allozymes as well as quantitative traits may only occur under specific conditions. Responses to toxins illustrate how adaptive changes can be based on major genes with polygenic modifiers. Analyses of continuous variation in ecologically relevant traits suggest low levels of heritable variation in some natural situations and emphasize the importance of genetic interactions. It is still not clear if adaptive responses in quantitative traits tend to involve major or minor genes. There is some evidence for genetic tradeoffs among environments and life history traits. Low levels of genetic variation, tradeoffs, and gene flow may restrict distributions and habitats occupied by species, but their relative importance remains unclear.

Animals↗
PubMed1994

Cytoplasmic incompatibility in Australian populations of Drosophila melanogaster.

In Drosophila melanogaster, weak incompatibility in crosses between infected and uninfected strains is associated with a Wolbachia microorganism. Crosses between infected males and uninfected females show a reduction (15-30%) in egg hatch. Progeny tests indicated that the infection is widespread in Australian D. melanogaster populations and that populations are polymorphic for the presence of the infection. The infection status of 266 lines from 12 populations along the eastern coast of Australia was determined by 4',6-diamidino-2-phenylindole (DAPI) staining of embryos. All populations contained both infected and uninfected flies. Infection frequencies varied between populations but there was no discernible geographical pattern. Laboratory experiments indicated that the infection was not associated with a reduction in fecundity as in Drosophila simulans. Incompatibility levels could not be increased by laboratory selection on isofemale lines. Factors contributing to the persistence of the infection in D. melanogaster populations are discussed.

Alphaproteobacteria↗
PubMed1994

Genetic and maternal variation for heat resistance in Drosophila from the field.

In Drosophila, field heritability estimates have focused on morphological traits and ignored maternal effects. This study considers heritable variation and maternal effects in a physiological trait, heat resistance. Drosophila were collected from the field in Melbourne, Australia. Resistance was determined using knock-down time at 37 degrees. Drosophila melanogaster was more resistant than Drosophila simulans, and males tended to be more resistant than females. Field heritability and maternal effects were examined in D. simulans using the regression of laboratory-reared F1 and F2 onto field-collected parents. Males from the field were crossed to a laboratory stock to obtain progeny. The additive genetic component to variation in heat resistance was large and significant, and heritability was estimated to be around 0.5. A large maternal effect was also evident. Comparisons of regression coefficients suggested that the maternal effect was not associated with cytoplasmic factors. There was no correlation between body size (as measured by wing length) and heat resistance. Unlike in the case of morphological traits, the heritability for heat resistance in nature is not less than that measured in the laboratory.

Adaptation, Physiological↗
PubMed1992

Dynamics of cytoplasmic incompatibility and mtDNA variation in natural Drosophila simulans populations.

In Drosophila simulans a cytoplasmically transmitted microorganism causes reduced egg hatch when infected males mate with uninfected females. The infection is rapidly spreading northward in California. Data on a specific mtDNA restriction site length polymorphism show that changes in the frequency of mtDNA variants are associated with this spread. All infected flies possess the same mtDNA allele, whereas the uninfected flies are polymorphic. Given that both paternal inheritance of the infection and imperfect maternal transmission have been demonstrated, one might expect instead that both infected and uninfected flies would possess both mtDNA variants. Our data suggest that imperfect female transmission of the infection (and/or the loss of the infection among progeny) is more common in nature than paternal transmission. A simple model of intrapopulation dynamics, with empirically supported parameter values, adequately describes the joint frequencies of the mtDNA variants and incompatibility types.

Animals↗
PubMed1991

Rapid spread of an inherited incompatibility factor in California Drosophila.

In Drosophila simulans in California, an inherited cytoplasmic incompatibility factor reduces egg hatch when infected males mate with uninfected females. The infection is spreading at a rate of more than 100 km per year; populations in which the infection was rare have become almost completely infected within three years. Analyses of the spread using estimates of selection in the field suggest dispersal distances far higher than those found by direct observation of flies. Hence, occasional long-distance dispersal, possibly coupled with local extinction and recolonization, may be important to the dynamics. Incompatibility factors that can readily spread through natural populations may be useful for population manipulation and important as a post-mating isolating mechanism.

Animals↗
PubMed1990

Factors affecting the distribution of cytoplasmic incompatibility in Drosophila simulans.

In Drosophila simulans a Wolbachia-like microorganism is responsible for reduced egg-hatch when infected males mate with uninfected females. Both incompatibility types have previously been found in North America, Europe and Africa. Some California populations have remained polymorphic for over two years, and the infection is apparently spreading in central California. Egg hatch proportions for wild-caught females from polymorphic populations show that the incompatibility system acts in nature, but egg mortality rates are apparently lower than observed in laboratory populations. Although infected females maintained under various laboratory conditions never produce uninfected offspring, some wild-caught infected females produce both infected and uninfected progeny. This helps explain the persistence of a low frequency of uninfected flies in predominantly infected populations and may also explain the other polymorphisms observed. Fitness comparisons of infected and uninfected stocks, including both larval and adult fitness components, indicate that fecundity may be the component most affected. Infected females suffer a fecundity reduction of 10-20% in the laboratory, but the reduction seems to be smaller in nature. A theoretical analysis provides some insight into the population biology of the infection.

Aging↗
PubMed1989

Geographic variation in the territorial success of Drosophila melanogaster males.

Drosophila melanogaster males defend food against other males to increase their access to females on food. The territorial behavior of stocks collected from Townsville, Corindi, and Melbourne on the east coast of Australia were compared. Males from these stocks showed the same incidence of territorial encounters. However, Melbourne males were more successful at obtaining territories in competition with Townsville or Corindi males. This difference could be accounted for largely by variation in body weight, although territorial success was also determined by other factors because Townsville and Corindi males that held territories were not heavier than Melbourne males. In reciprocal crosses between the populations there was directional dominance for increased territorial success. F1 males were of intermediate weight and F1 males that held territories tended to be lighter than territorial Melbourne males. Melbourne males were more successful than Townsville males because they tended to win escalated encounters, resulting in displacement of territory residents.

Animals↗
PubMed1989

Selection for increased desiccation resistance in Drosophila melanogaster: additive genetic control and correlated responses for other stresses.

Previously we found that Drosophila melanogaster lines selected for increased desiccation resistance have lowered metabolic rate and behavioral activity levels, and show correlated responses for resistance to starvation and a toxic ethanol level. These results were consistent with a prediction that increased resistance to many environmental stresses may be genetically correlated because of a reduction in metabolic energy expenditure. Here we present experiments on the genetic basis of the selection response and extend the study of correlated responses to other stresses. The response to selection was not sex-specific and involved X-linked and autosomal genes acting additively. Activity differences contributed little to differences in desiccation resistance between selected and control lines. Selected lines had lower metabolic rates than controls in darkness when activity was inhibited. Adults from selected lines showed increased resistance to a heat shock, 60Co-gamma-radiation, and acute ethanol and acetic acid stress. The desiccation, ethanol and starvation resistance of isofemale lines set up from the F2s of a cross between one of the selected and one of the control lines were correlated. Selected and control lines did not differ in ether-extractable lipid content or in resistance to acetone, ether or a cold shock.

Acetates↗
PubMed1987

Residual influences on fecundity in drosophilid species.

A residual influence of males and females on oviposition has been examined in 7 drosophilids. There was evidence for oviposition deterrence in Drosophila funebris, with males as well as females producing the inhibitory effect. In contrast, male residues stimulated oviposition in Zaprionus tuberculatus. Male residues also stimulated oviposition and appeared to serve as an aggregation cue in D. melanogaster.

Animals↗
PubMed1986

Genetic divergence under uniform selection. II. Different responses to selection for knockdown resistance to ethanol among Drosophila melanogaster populations and their replicate lines.

We have tested the hypothesis that genetic differences among conspecific populations may result in diverse responses to selection, using natural populations of Drosophila melanogaster. Selection for ethanol tolerance in a tube measuring knockdown resistance was imposed on five West Coast populations. In 24 generations the selected lines increased their mean knockdown times, on average, by a factor of 2.7. An initially weak latitudinal cline was steepened by selection. The two southernmost populations showed the same increases in the selected character, but differed consistently in their correlated responses in characters related to ethanol tolerance. This result indicates that the populations responded to selection by different genetic changes. Selection decreased female body weight and increased resistance to acetone, suggesting components of the response unrelated to ethanol metabolism. The Adhs allele was favored by selection in all populations at the onset, but increased in frequency only in the selected lines of the southernmost population. There was a correlation between latitude and Adh frequency changes, suggesting that fitnesses of the Adh alleles were dependent on the genetic background. Genetic background also had a large effect on the loss of fitness due to selection. Genetic drift between replicate lines caused more variation in selection response than initial genetic differences between populations. This result demonstrates the importance of genetic drift in divergence among natural populations undergoing uniform selection, since the effective population sizes approached those of small natural populations. Drift caused greater divergence between selected replicates than control replicates. Implications of this result for the genetic model of selection response are discussed.

Alcohol Dehydrogenase↗
PubMed1975

Comparison of DNA binding in normal population, general hospital laboratory personnel, and personnel from laboratories studying SLE.

Sera from 18 of 56 individuals working in SLE laboratories bound more than 30 per cent of 0.1 mug of 125-I denatured calf thymus DNA, in an ammonium sulfate precipitation assay. Only two of 58 normal non-laboratory personnel and four of 40 sera from routine hospital laboratory personnel bound more than 30 per cent. Statistical analysis of these results with the Kolmogorov-Smirnov nonparametric test indicated this was a very significant difference (p less than .001). Using native DNA as a test antigen a similar pattern was seen, but it was not as clear cut. Part of this increased reactivity is heat labile. Further studies must be carried out before an adequate interpretation of these findings is possible.

Animals↗