Dynamics of the genetic structure in experimental Drosophila populations for the Adh locus as affected by ethanol

Electrophoresis method was used to analyze the genetic structure of four experimental Drosophila populations (the control one and those with 5, 10 and 15% of ethanol in the nutrient medium) with initial frequency of AdhF = 0.5 for 50 monitoring generations. It was established that F and S alleles had different selective values. Natural selection favoured the F-allele. Addition of ethanol to the nutrient medium increased the selection intensity in the first 15 generations but did not change the relative adaptability of three genotypes. This caused a similarity of genetic structure in experimental populations during 50 generations.     

Genetic structure of the experimental population of Drosophila melanogaster polymorphic with respect to beta-carboxyesterase locus

The polymorphism of beta-phile carboxyesterase (E.C.3.1.1.2) in the males and females of the wild type (Odessa 1) experimental population of Drosophila melanogaster Meigen has been studied with the polyacrylamide disc-electrophoresis. Two isoforms of the enzyme and three phenotypic classes non-uniformly presented among the males and females have been detected. The frequencies of the alleles encoding the corresponding isoforms of the beta-phile carboxyesterase have been determined, as well as those of the genotypes that differed qualitatively and quantitatively with respect to the investigated gene-enzyme system. The deviations of the detected genotype frequencies from the theoretically expected ones were determined. The role of the natural selection directed towards the decreasing of the frequencies of the certain allele is discussed.     

Effect of breeding structure on population genetic parameters in Drosophila

The breeding structure of populations has been neglected in studies of Drosophila, even though Wright and Dobzhansky's pioneering work on the genetics of natural populations was an attempt to tackle what they regarded as an essential factor in evolution. We compared the breeding structure of sympatric populations of D. melanogaster and D. simulans, two sibling species that are widely used in evolutionary studies. We recorded changes in population density and microsatellite variation patterns for 3 years in a temperate environment of southwestern France. Results were distinctively different in the two species. Maximum population levels in summer and in autumn were similar and fluctuated greatly over years, each species being in turn the most abundant. However, genetic data showed that D. melanogaster made up a continuous breeding population in time and space of practically infinite effective size. D. simulans was fragmented into isolates with a local effective size of between 50 and 350 individuals. A consequence of this was that, while a local sample provided a reliable estimate of regional genetic variability in D. melanogaster, a sample from the same area provided an underestimate of this parameter in D. simulans. In practical terms, this means that variations in breeding structure should be accounted for in sampling schemes and in designing evolutionary genetic models. More generally, this suggests the existence of differential reactions to local environments that might contribute to several genomic differences observed between these species.     

A genetic locus affecting the developmental expression of an enzyme in Drosophila melanogaster

We have discovered and characterized strains of Drosophila melanogaster showing a genetically controlled modification of the developmental program for accumulation of aldehyde oxidase. Most strains show a sharp increase in specific activity just before pupation. The variant class, represented by several strains, does not show the increase at this stage even though changes in specific activity at other stages are comparable in the two classes. This developmental difference is controlled by a single gene or a small chromosome segment closely linked to the structural gene and apparently exercising cis-dominant control over its expression. It is hoped that this and other similar mutations currently under study will provide some insight into the organization of regulatory loci in the eukaryotic genome.     

The genetic structure of the Raleigh natural population of Drosophila melanogaster revisited

The Raleigh natural population of Drosophila melanogaster was reanalyzed with special attention to possible dysgenic effects during the extraction of chromosomes. About 600 second chromosomes were extracted from the Raleigh natural population, half in the cytoplasm of wild-caught females (native genetic background) and half in the cytoplasm of the laboratory line, C160(In(2LR)SM1, Cy/In(2LR)bw(V1)) (foreign genetic background). We could not find significant differences between the two extraction schemes in the frequency of lethal second chromosomes (Q = 0.252 for the lines with the negative genetic background vs. 0.231 for the lines with the foreign genetic background) or in the homozygous detrimental (D) and lethal (L) loads (D = 0.210 vs. 0.251; L = 0.287 vs. 0.264). The effective size of the population was estimated to be approximately 19,000, based on the allelism rate of lethal-bearing chromosomes. The homozygous load markedly decreased in the 15 years since a previous study of the same population.     

The structure of the Adh locus of Drosophila mettleri: an intermediate in the evolution of the Adh locus in the repleta group of Drosophila.

Members of species of the mulleri and hydei subgroups of the repleta group of Drosophila have duplicate Adh genes. The Adh regions of D. mojavensis, D. mulleri, and D. hydei contain three genes--a pseudogene, Adh-2, and Adh-1--arranged 5' to 3'. To understand the evolution of the triplicate Adh structure, we have cloned and sequenced the Adh locus of D. mettleri. This region consists of a 5' pseudogene and a 3' functional Adh gene. On the basis of the structure and nucleotide sequence comparisons of Adh genes of D. mettleri and other species, we propose that an initial duplication of the ancestral Adh gene generated two Adh genes arranged in tandem. The more 5' Adh gene became a pseudogene, while the more 3' gene remained functional through all the developmental stages. A second duplication of this 3' gene resulted in Adh regions with three genes--a pseudogene, Adh-2, and Adh-1.     

Natural killer activity in man under different experimental conditions]

The cytotoxic activity of natural killer (NK) cells against labelled with 3H-uridine target cells of standard human erythromyeloblast line K562 in 63 healthy donors was studied in 14-hr cytotoxic test. The cytotoxic reaction was realized in complete medium supplemented with different types of serum such as foetal calf serum (FCS), autologous or homologous sera in different schemes of incubation. It has been shown that NK cell activity was augmented by 50 per cent (p < 0.05) in the presence of homologous serum added to mononuclear cell suspension for 1 hr at 37 degrees C in comparison with the effect of FCS presence. Thus, the serum of healthy donors contains some factors which not only reflect an individual genotypic information of a donor, but also can be recognized by NK cells and significantly change the cytotoxic NK cell activity. The data obtained exclude possibility of using a homologous serum when positive controls for natural cytotoxic reactions are planned.     

Origin of spatial genetic structure in an expanding oak population

Spatial genetic structure (SGS) results from the interplay of several demographical processes that are difficult to tease apart. In this study, we explore the specific effects of seed and pollen dispersal and of early postdispersal mortality on the SGS of a seedling cohort (N = 786) recruiting within and around an expanding pedunculate oak (Quercus robur) stand. Using data on dispersal (derived from parentage analysis) and mortality (monitored in the field through two growing seasons), we decompose the overall SGS of the cohort into its components by contrasting the SGS of dispersed (i.e. growing away from their mother tree) vs. nondispersed (i.e. growing beneath their mother tree) and initial vs. surviving seedlings. Patterns differ strongly between nondispersed and dispersed seedlings. Nondispersed seedlings are largely responsible for the positive kinship values observed at short distances in the studied population, whereas dispersed seedlings determine the overall SGS at distances beyond c. 30 m. The paternal alleles of nondispersed seedlings show weak yet significantly positive kinships up to c. 15 m, indicating some limitations in pollen flow that should further promote pedigree structures at short distances. Seedling mortality does not alter SGS, except for a slight increase in the nondispersed group. Field data reveal that mortality in this group is negatively density‐dependent, probably because of small‐scale variation in light conditions. Finally, we observe a remarkable similarity between the SGS of the dispersed seedlings and that of the adults, which probably reflects dispersal processes during the initial expansion of the population. Overall, this study demonstrates that incorporating individual‐level complementary information into analyses can greatly improve the detail and confidence of ecological inferences drawn from SGS.     

Conserving genetic variability of a wild insect population under laboratory conditions

Drosophila melanogaster (Meigen) was used to test the power of isofemale lines in preserving genetic variability. We performed experiments in two ways. One series consisted of measuring the genetic variability for three enzymatic loci in 32 isofemale lines, in the first and 23^rd generations of culture. In the second series, we tested the capacity of the larvae to eliminate a parasitoid by encapsulation after eight years of laboratory breeding. In general, individual isofemale lines appeared to change during the 23 generations of the study, but the global frequency of these alleles among the 32 isofemale lines stayed relatively unchanged. The only rare allele observed was also conserved. Changes in allozyme frequencies at any one locus were independent of those at other loci. Genetic variation of a biological trait, the capacity of the larvae to encapsulate a parasitoid, also changed, but it could be restored to a level close to that of the starting population by mass hybridizing together individuals of each line.

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Résumé D. melanogaster (Meigen) a été utilisé pour tester la capacité des lignées isofemelles à conserver la variabilité génétique d'une population naturelle. Deux types d'expériences ont été réalisées. L'une a consisté à déterminer la variabilité génétique de 3 locus enzymatiques pour 32 lignées isofemelles à la première et à la 23^ème génération d'élevage au laboratoire. L'autre a consisté à tester la capacité des larves à éliminer un parasito?de par le processus d'encapsulation après 8 années d'élevage au laboratoire. D'une fa?on générale, certaines lignées isofemelles perdent de la variabilité durant les 23 générations de l'étude. Mais la fréquence globale des allèles reste inchangée si l'on considère l'ensemble des 32 lignées. Le seul allèle rare observé a également été conservé. Les modifications des fréquences allèliques à chacun des locus ont lieu de fa?on indépendante les unes des autres. La variabilité génétique d'un caractère biologique, la capacité des larves à encapsuler le parasito?de, a également varié, mais elle a pu être restaurée à un niveau proche de la population initiale en rassemblant plusieurs individus de chacune des lignées.

     

Workers' sons rescue genetic diversity at the sex locus in an invasive honey bee population

The hallmark of eusociality is the division of labour between reproductive (queen) and nonreproductive (worker) females. Yet in many eusocial insects, workers retain the ability to produce haploid male offspring from unfertilized eggs. The reproductive potential of workers has well‐documented consequences for the structure and function of insect colonies, but its implications at the population level are less often considered. We show that worker reproduction in honey bees can have an important role in maintaining genetic diversity at the sex locus in invasive populations. The honey bee sex locus is homozygous‐lethal, and, all else being equal, a higher allele number in the population lead to higher mean brood survival. In an invasive population of the honey bee Apis cerana in Australia, workers contribute significantly to male production: 38% of male‐producing colonies are queenless, and these contribute one‐third of all males at mating congregations. Using a model, we show that such male production by queenless workers will increase the number of sex alleles retained in nascent invasive populations following founder events, relative to a scenario in which only queens reproduce. We conclude that by rescuing sex locus diversity that would otherwise be lost, workers' sons help honey bee populations to minimize the negative effects of inbreeding after founder events and so contribute to their success as invaders.