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V Loeschcke

Publications and source records attributed to V Loeschcke.

53 records · Page 3Linked to original sources
PubMed1998

Stress temperatures and quantitative variation in Drosophila melanogaster.

Using an isofemale line analysis, we analysed the consequences of extreme rearing temperatures for genetic variation in quantitative characters in Drosophila melanogaster. Three types of characters were used: life history (viability and developmental time), body size (thorax length and wing length) and meristic (number of sternopleural chaetae and number of arista branches). Phenotypic variation significantly increased under stress conditions in all morphological characters studied; for viability, it increased at the low stress temperature. Genetic variation, measured by the coefficient of intraclass correlation, was generally higher at both low and high stress temperatures for thorax length and sternopleural chaeta number. For wing length and viability, genetic variation was higher at the low extreme temperature. No consistent trend was found for genetic variation in arista branch number and developmental time. Our results agree with the hypothesis that genetic variation is increased in stressful environments. A possible mechanism underlying this phenomenon is briefly discussed.

Animals↗
PubMed1998

Population differentiation through mutation and drift--a comparison of genetic identity measures.

Different genetic identity or distance measures are compared that consider allelic variation within and between populations. Particularily we analyse those suggested by Nei (IS, DS), Rogers (DR), Reynolds, Weir and Cockerham (D theta), Nei, Tajima and Tateno (DA), Tomiuk and Loeschcke (ITL, DTL) and Goldstein et al. ((delta mu)2). The simulations focus on the influence of non-equilibrium conditions on the stability of these measures. The degree of homozygosity of an ancestral population before it splits into two sister populations is most important for the stability of the different estimates of genetic identity. If populations are not close to their equilibrium homozygosity, a considerable bias can occur and, thereby, provide very misleading estimates of the time span since divergence. The ITL-measure based on estimates of ancestral alleles is more robust than other measures of genetic identity, especially for large population sizes and high mutation rates. For the infinite allele model, the analysis shows that more precise estimates of the frequency of ancestral alleles can greatly improve the reliability of the estimate of genetic identity in the case of ITL. For the stepwise mutation model, the TL-measure combines the attributes of the DA- and (delta mu)2-measures. The TL-measure is efficient for the construction of the correct tree topology of related populations as well as for the estimation of the branch length when protein or microsatellite data are analysed.

Alleles↗
PubMed1997

High-temperature stress and the evolution of thermal resistance in Drosophila.

The evolution of thermal resistance and acclimation is reviewed at the population level using populations and isofemale lines of Drosophila buzzatii and D. melanogaster originating from different climatic regions. In general, ample genetic variation for thermal resistance was found within and among populations. A rough correlation between the climate of origin and thermal resistance was apparent. Acclimation at a non-lethal temperature led to a significant increase in survival after heat shock, and recurrent acclimation events generally increased survival even further. Acclimation effects lasted over several days, but this effect decreased gradually with time since acclimation. Protein studies showed that the concentration of Hsp70 in adult flies is greatly increased by acclimation and thereafter gradually decreases with time. For populations with relatively high survival at one life stage, survival often was low at other life stages. Furthermore, selection on different life stages showed that a selection response in one life stage did not necessarily result in a correlated response in another. These observations indicate that different mechanisms or genes at least in part are responsible for or are expressed at different developmental stages. Selection for increased resistance was successful despite low heritabilities for the trait. Survival and fertility were compared between acclimated and non-acclimated flies, and a cost of expressing the "heat shock response" was identified in that increased survival after acclimation was accompanied by reduced fertility. The relative costs increased under nutritional stress. Metabolic rate was genetically variable but did not correlate with temperature resistance. The more resistant lines, however, often had shorter developmental time. Inbreeding reduced thermal stress tolerance of adult flies, but it did not reduce tolerance of embryos that possibly are exposed to strong natural selection for thermal stress resistance. In general, inbreeding may reduce stress resistance, and thus multiple stressful events may account for increased inbreeding depression in harsh environments.

Acclimatization↗
PubMed1997

Estimating heritability in a threshold trait: heat-shock tolerance in Drosophila buzzatii.

Stress tolerance is often measured as a threshold trait, the proportion of a group that survives a defined stress regime. Requirements of large offspring numbers coupled with fitness variation in the surviving cohort limit the use of some standard genetic analyses for estimating heritability. Therefore, we present an isofemale line analysis, which is a modified full-sib design, to estimate heritability of tolerance to heat shock in pretreated Drosophila buzzatii adults. Highly significant levels of genetic variation were found in males and females at the third generation of laboratory rearing, and the intraclass correlations were estimated to be about 0.2 for four independent sets of 25 isofemale lines. The proportion of the variance explained within lines among same-sex replicates, however, was larger than that between replicates of males and females. Because genetic variation was estimated from groups, the error variation required factoring by the group size to estimate heritability, which averaged 0.03. The four most tolerant, four least tolerant and four lines of average tolerance to heat stress in each set were reanalysed after 10-11 generations of rearing at 25 degrees C. Survival in the 13th-14th generations was positively and significantly associated with survival at generation 3. These comparisons indicate the high repeatability of measurements of heat-shock tolerance.

Animals↗
PubMed1997

A combined DNA-microsatellite and isozyme analysis of the population structure of the harbour porpoise in Danish waters and west Greenland.

One hundred and twenty-four specimens of the harbour porpoise, Phocoena phocoena, occurring in inner Danish waters (IDW), the North Sea and West Greenland were analysed to study subdivision into genetically differentiated subpopulations using PCR-amplified DNA-microsatellites and isozyme markers. Three polymorphic microsatellites, 415/416, 417/418 and Igf-I (insulin-like growth factor I) were detected with nine, eight and 15 alleles, respectively, and from a former study two polymorphic isozymes, Mpi-1 and Pgm, with three and two alleles, respectively, were used in the analysis. Overall deviations from the expected Hardy-Weinberg distribution were only observed in the total sample and at a single locus in the North Sea-summer sample and at two loci in the West Greenland sample. Whenever this occurred a surplus of homozygotes was observed, suggesting a Wahlund effect, a null allele or nonrandom mating. The analysis of the genetical population structure showed that harbour porpoises from West Greenland, the North Sea and IDW were three geographically, genetically differentiated populations even though connected through some degree of gene flow. A tendency for females to be more stationary than males was suggested. Furthermore, the population structure suggested a closer relationship between IDW and the North Sea.

Animals↗
PubMed1997

Effects of inbreeding in three life stages of Drosophila buzzatii after embryos were exposed to a high temperature stress.

The interaction between inbreeding and high-temperature stress was examined in the cactophilic fruit fly, Drosophila buzzatii. Embryos of four inbreeding levels (F = 0, F = 0.25, F = 0.375, F = 0.5) were either maintained at 25 degrees C throughout egg-to-adult development or were exposed to 41.5 degrees C for 110 min at an age of 20 h. Hatching, larva-to-pupa survival, pupa-to-adult survival, and egg-to-adult survival were estimated. Heat shock reduced hatching rates, but survival to adulthood for individuals that hatched was unaffected by the heat shock. Inbreeding reduced the proportion of eggs hatching in the 25 degrees C control group only. For larva-to-pupa and pupa-to-adult survival there was no interaction between inbreeding and stress. The effect of inbreeding on egg-to-adult survival was stronger in the 25 degrees C control group compared with the group exposed to heat shock. The results imply environmental dependency of inbreeding depression and suggest that stress tolerance may not always be reduced by inbreeding. The thermal microenvironment of cactus rots in the field was assessed by measuring temperatures inside 17 rots. Internal rot temperatures varied with a maximum temperature of 48 degrees C during the day. Selection for temperature tolerance in nature may have depleted genetic variation for this trait limiting the effect of inbreeding on thermal resistance.

Animals↗
PubMed1996

A maximum-likelihood estimator of the genetic identity between polyploid species.

Based on a recently proposed method for estimating the genetic identity between polyploid species, maximum-likelihood estimators are given for the genetic identity between polyploid species, for the ancestral degree of homozygosity and their variances. As an example, the genetic identity, the ancestral degree of homozygosity and their variances were estimated from data sets of populations of two species, the weevil Polydrusus mollis and the salamander Ensatina complex. It was found that other indices of the genetic identity between species obviously underestimate genetic identity due to the pooling of differences caused by mutation and drift.

Animals↗
PubMed1996

Acclimation and selection for increased resistance to thermal stress in Drosophila buzzatii.

Direct selection for increased resistance to a heat shock (41.9 degrees for 90 min) was carried out using two replicate lines of Drosophila buzzatii that were derived from a large base population. Selected individuals were first acclimated to high temperature before selection, while control individuals were acclimated but not selected, and selection was performed every second generation. Resistance to heat shock with acclimation increased in selected lines. Without acclimation, a correlated smaller increase in heat-shock resistance was suggested. Survival of males was higher than that of females in all lines when tested with acclimation, but with direct exposure to high temperatures, survival of females was greater than that of males both in selection and control lines but not in the base population. From analysis of reciprocal cross progeny between lines, one selection line was found to possess a dominant autosomal factor that significantly increased resistance of males much more than resistance of females. Also suggestive was recessive traits on the X chromosome in both selection lines that increased thermotolerance. No cytoplasmic effects were found. After accounting for other effects, survival of F1 flies was intermediate, suggesting that additive variation is present for one or more of the autosomes.

Animals↗
PubMed1996

Heat-shock resistance in Drosophila populations: analysis of variation in reciprocal cross progeny.

Genetic variation for resistance to high temperature stress was studied in populations of D. melanogaster and D. buzzatii from different geographic regions. Drosophila melanogaster individuals were presented with either a direct short exposure to a high temperature or exposure to high temperature after receiving a pretreatment, which increased resistance. Heat-stress resistance varied among populations, with one much more resistant than all others under both treatments. Another possessed low stress resistance when exposed without the heat pretreatment; but with pretreatment, resistance increased relative to the other populations. Evidence from reciprocal crosses suggests that the X chromosome of the more resistant population carries alleles that greatly increase resistance, and that one or more factors on the autosomes also affect resistance. Non-additive interaction effects among the three less resistant population, were suggestive that all differ for various elements that contribute to stress resistance, and that some clearly change inducible resistance more than basal levels. In D. buzzatii, the two least resistant populations were genetically very similar. Crosses to the more resistant population gave results suggesting that the low resistance to heat is dominant. A small X-chromosome effect that increased resistance, and a dominant enhancer of male resistance also may have contributed to variation in resistance.

Analysis of Variance↗
PubMed1995

Heat-shock tolerance and inbreeding in Drosophila buzzatii.

The effect of inbreeding on survival after a short-term heat shock was tested for two age groups of the cactophilic fruit fly, Drosophila buzzatii, reared under nonstress conditions. Four inbreeding levels (F = 0, F = 0.25, F = 0.375, F = 0.5) were generated by outcrossing or full-sib mating. All flies were conditioned at 36.5 degrees C for 75 min prior to exposure to stress, to activate the synthesis of heat-shock proteins. These proteins are known to protect cells against stress damage. The younger group of flies were exposed to a thermal stress of 40.7 degrees C for 88 min, 103 min, or 118 min and the older flies to the same temperature only for 88 min or 103 min, as the survival of older flies after heat stress was much lower than that of the younger flies. Survival after heat shock declined with increased inbreeding in both age groups. For the younger flies, the slope of the regression line, F, on survival was lower at higher stress levels. For the older flies, inbreeding effects were similar at both stress levels. Mortality without stress also differed significantly among inbreeding groups, mainly because of a large difference between the F = 0.5 group and all others.

Adaptation, Physiological↗
PubMed1994

Multi-species risk analysis, species evaluation and biodiversity conservation.

The multi-species conservation approaches starting from Vane-Wright et al. (1991) search for a biologically valid basis to evaluate biodiversity. Such evaluations can be used to optimize reserve boundaries so reserves contain a high level of biodiversity. However, these optimization procedures do not minimize the future loss of biodiversity. We provide a method that can be used to minimize the loss of biodiversity. The method integrates an evolutionary species evaluation with an ecological multi-species risk analysis to estimate the expected loss of phylogenetic diversity. A minimization of this loss will optimize the preservation of phylogenetic diversity.

Biological Evolution↗
PubMed1994

Response to environmental change: genetic variation and fitness in Drosophila buzzatii following temperature stress.

Drosophila buzzatii typically may encounter high temperatures in nature, and this species is genetically variable for resistance to stress, both within and among populations. Fitness of survivors to stress, however, was reduced, and observed as a reduction in male fertility and female fecundity. With time following exposure to severe stress, reproductive capacity improved, but lifetime offspring production still was reduced significantly. This effect would greatly reduce a population's recovery from small size, which could occur following exposure to some man-made or environmental extreme. Although the results presented here were obtained for effects of heat stress, such consequences likely apply to a wide range of natural and man-made environmental stresses, including heavy metal toxicity or other pollutants. Low levels of these pollutants may not cause an observable effect on populations, even if some individuals are killed or offspring production is decreased. If genetic variation for resistance is present, higher tolerance may evolve. However, if concentrations are permitted to rise too far, some stress threshold may be reached, as observed for thermal stress, causing mass die-off or sterility and, possibly, local extinction. Understanding the effects of stress is important when preparing programs for the conservation of species. Organisms generally do not become extinct when resources are abundant and the climate benign, but unfortunately, no guarantee can be made that environmental conditions in any locality will remain stable over a long time. Consequently, a high possibility of exposure to an extreme stress in an area would greatly reduce its usefulness as a reserve. Likewise, when choosing organisms for reintroduction, stress resistance of the chosen individuals and high levels of genetic variation within a population would be valuable. The organisms placed there must be able to change. Analysis of stress resistance (at non-lethal levels) among either family groups or for different populations would be very useful when deciding which individuals to reintroduce to an area or place in a reserve. Additionally, analysis may suggest that stress resistance is very low in a population or species. If identified, particular care may be taken to monitor the occurrence of that stress in the environment, and to take action to protect the population from that stress. Preservation of species should be designed for the future, with the goal to preserve, not simply to postpone extinction.

Analysis of Variance↗
PubMed1984

Evolution and intraspecific exploitative competition. II. A two-locus model for additive gene effects.

A two-locus model corresponding to the model of Christiansen and Loeschcke (1980, theoret, Popul. Biol. 18, 297-313) is analysed. The two loci each have two alleles, and the loci influences a character which determines the utilization of resources in a one-dimensional continuum. The analysis of the model is supported by numerical iterations of the recurrence equations. The previous prediction of high linkage disequilibrium for small allele contributions to the character and close linkage between the loci is confirmed. For larger allele contributions results comparable to those for the symmetric viabilities model are obtained. The model degenerates when the allele contributions at the two loci are equal, i.e., in the most symmetric situation. The results are discussed as the outcome of a balance between optimizing selection and disruptive selection. For small allele contributions the results are virtually independent of which genotype is most favoured by the optimizing aspect of the selective forces.

Alleles↗
PubMed1976

Analysis of intercellular distributions of chromatid aberrations.

59 intercellular distributions of chemically induced and spontaneous chromatid aberrations were analyzed for goodness of fit in respect of the Poisson (PD), the geometrical (GD), and the negative binomial distributions (NBD). The data are excellently described by the NBD. This distribution can be deduced from a model out of the queueing theory and is based on the hypothesis of restitution. Estimators are obtained for the ratio of restitution and induction processes involved in the origin of chromosomal aberrations.

Alkylating Agents↗
PubMedDate not supplied

Altitudinal patterns for longevity, fecundity and senescence in Drosophila buzzatii.

We tested for variation in longevity, senescence rate and early fecundity of Drosophila buzzatii along an elevational transect in Argentina, using laboratory-reared flies in laboratory tests performed to avoid extrinsic mortality. At 25 degrees C, females from lowland populations lived longer and had a lower demographic rate of senescence than females from highland populations. Minimal instead of maximal temperature at the sites of origin of population best predicted this cline. A very different pattern was found at higher test temperature. At 29.5 degrees C, longevity of males increased with altitude of origin of population. No clinal trend was apparent for longevity of females at 29.5 degrees C. There was evidence for a trade-off between early fecundity and longevity at non-stressful temperature (25 degrees C) along the altitudinal gradient. This trait association is consistent with evolutionary theories of aging. Population-by-temperature and sex-by-temperature interactions indicate that senescence patterns are expressed in environment specific ways.

Aging↗