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1.
Summary The present paper deals with crossing experiments on translocation heterozygotes in the mosquitoCulex pipiens L. It is shown that the ratio of euploid and aneuploid gametes is determined by two allelomorphs of one single inheritable factor. These experiments agree with our hypothesis that the ratio of segregation types in a translocation heterozygous organism (alternate and adjacent) is determined by a series of multiple alleles of a single mendelian factor.The investigations were done in the Department of Biology (21) of the Johannes Gutenberg-University in Mainz.  相似文献   

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The α-proteobacteria Wolbachia are among the most common intracellular bacteria and have recently emerged as important drivers of arthropod biology. Wolbachia commonly act as reproductive parasites in arthropods by inducing cytoplasmic incompatibility (CI), a type of conditional sterility between hosts harboring incompatible infections. In this study, we examined the evolutionary histories of Wolbachia infections, known as wPip, in the common house mosquito Culex pipiens, which exhibits the greatest variation in CI crossing patterns observed in any insect. We first investigated a panel of 20 wPip strains for their genetic diversity through a multilocus scheme combining 13 Wolbachia genes. Because Wolbachia depend primarily on maternal transmission for spreading within arthropod populations, we also studied the variability in the coinherited Cx. pipiens mitochondria. In total, we identified 14 wPip haplotypes, which all share a monophyletic origin and clearly cluster into five distinct wPip groups. The diversity of Cx. pipiens mitochondria was extremely reduced, which is likely a consequence of cytoplasmic hitchhiking driven by a unique and recent Wolbachia invasion. Phylogenetic evidence indicates that wPip infections and mitochondrial DNA have codiverged through stable cotransmission within the cytoplasm and shows that a rapid diversification of wPip has occurred. The observed pattern demonstrates that a considerable degree of Wolbachia diversity can evolve within a single host species over short evolutionary periods. In addition, multiple signatures of recombination were found in most wPip genomic regions, leading us to conclude that the mosaic nature of wPip genomes may play a key role in their evolution.  相似文献   

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Wolbachia are maternally inherited endosymbiotic bacteria that infect many arthropod species and may induce cytoplasmic incompatibility (CI), resulting in abortive embryonic development. One Wolbachia host, Culex pipiens complex mosquitoes, displays high levels of variability in both CI crossing types (cytotypes) and DNA markers. We report here an analysis of 14 mosquito strains, containing 13 Wolbachia variants, and with 13 different cytotypes. Cytotypes were Wolbachia-dependent, as antibiotic treatment rendered all strains tested compatible. Cytotype distributions were independent of geographical distance between sampling sites and host subspecies, suggesting that Wolbachia does not promote a reproductive isolation depending on these parameters. Backcross analysis demonstrated a mild restoring effect of the nuclear genome, indicating that CI is mostly cytoplasmically determined for some crosses. No correlation was found between the phenotypic and genotypic variability of 16 WO prophage and transposon markers, except for the WO prophage Gp15 gene, which encodes a protein similar to a bacterial virulence factor. However, Gp15 is partially correlated with CI expression, suggesting that it could be just linked to a CI gene.  相似文献   

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Population genetics of insecticide resistance in the mosquito Culex pipiens   总被引:2,自引:0,他引:2  
Thirty years of control of the mosquito Culex pipiens using organophosphate insecticides (OP) has selected for OP-resistance alleles on a world-wide scale. As reviewed here, studies at the levels of gene and population allow identification of the main forces driving this process of adaptation. Three loci are involved in OP-resistance in C. pipiens. For two of these, adaptive mutations were found to be rare events, such that the ubiquitous distribution of certain resistance alleles could only be explained as deriving from a single origin by mutation followed by extensive migration. Population structure analyses confirmed that long-distance migration is frequent. Thus, different resistance alleles could accumulate and compete within populations soon after their origin by mutation. The different selection pressures acting on these alleles, i.e. their selective advantage in the presence of OP and their disadvantage (resistance cost) in absence of OP, were also analysed. Substantial differences in resistance cost among alleles present within the Mediterranean area were discovered. Long-term surveys of Mediterranean populations confirmed the pivotal importance of resistance cost in shaping the evolution of this adaptive polymorphism. Some hypotheses on the functional links between the nature of the initial mutation events and the subsequent evolution of polymorphism are discussed.  相似文献   

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The variation in copulatory activity in three strains of Culex pipiens is investigated and the results are discussed in relation to genetic control of mosquito populations.  相似文献   

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When any of the ten “rat essential” amino acids was omitted singly from a fully-defined synthetic dietary medium, newly-hatched Culex pipiens larvae were unable to develop to the second instar. With proline omitted, development was greatly retarded and survival to the adult stage reduced. Without aspargine (but not aspartic acid) growth and development ceased in most individuals before larval-pupal ecdysis, and no adults were obtained. These twelve amino acids are considered nutritionally essential for this mosquito. With glycine omitted singly, development was markedly retarded, but survival to the adult stage was not affected; thus this amino acid is required for good growth, but these experiments do not demonstrate it as essential. Single omission of alanine, aspartic acid, cysteine, glutamic acid or amide, serine or tyrosine had virtually no effect on development and they are therefore considered nutritionally non-essential. With diets containing the twelve culex-essential amino acids only, very little development occurred, but augmentation with either glycine or serine allowed growth and development almost as good as with the complete amino acid mixture. Augmentation of the essential twelve with alanine, cysteine, glutamic acid/amide, or tyrosine singly failed to improve development. The requirement for dietary asparagine shown by these studies appears to be unique among insects so far studied. In particular, another mosquito, Aedes aegypti, has no such requirement.  相似文献   

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One view of adaptation is that it proceeds by the slow and steady accumulation of beneficial mutations with small effects. It is difficult to test this model, since in most cases the genetic basis of adaptation can only be studied a posteriori with traits that have evolved for a long period of time through an unknown sequence of steps. In this paper, we show how ace-1, a gene involved in resistance to organophosphorous insecticide in the mosquito Culex pipiens, has evolved during 40 years of an insecticide control program. Initially, a major resistance allele with strong deleterious side effects spread through the population. Later, a duplication combining a susceptible and a resistance ace-1 allele began to spread but did not replace the original resistance allele, as it is sublethal when homozygous. Last, a second duplication, (also sublethal when homozygous) began to spread because heterozygotes for the two duplications do not exhibit deleterious pleiotropic effects. Double overdominance now maintains these four alleles across treated and nontreated areas. Thus, ace-1 evolution does not proceed via the steady accumulation of beneficial mutations. Instead, resistance evolution has been an erratic combination of mutation, positive selection, and the rearrangement of existing variation leading to complex genetic architecture.  相似文献   

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Ecotypic differentiation is well described in the mosquito Culex pipiens , separating populations breeding in subterranean and human-made sites (hypogeous habitat) from those in open-air sites (epigeous habitat). The pattern of population differentiation observed at the Aat-1 locus has been suspected to be associated with such ecotypic differentiation via habitat-dependent selection, but this supposition is still the subject of debate in the literature. We analysed differentiation patterns for Aat-1 and another four loci among populations from both habitat types in the French Alps. We showed that the Aat-1A allele is favoured within hypogeous habitats but selected against within epigeous habitats. Comparisons of our results with other data reported in the literature indicate that the Aat-1A allele is generally evolving under habitat-differential selection, but that the precise balance of migration and selection that determines equilibrium allele frequencies varies greatly across Europe. The nature of this habitat-dependent selection, and its resulting (geographically varying) equilibrium point, are discussed in relation to the biology of this mosquito species.  相似文献   

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Insecticide resistance genes have developed in a wide variety of insects in response to heavy chemical application. Few of these examples of adaptation in response to rapid environmental change have been studied both at the population level and at the gene level. One of these is the evolution of the overproduced esterases that are involved in resistance to organophosphate insecticides in the mosquito Culex pipiens. At the gene level, two genetic mechanisms are involved in esterase overproduction, namely gene amplification and gene regulation. At the population level, the co-occurrence of the same amplified allele in distinct geographic areas is best explained by the importance of passive transportation at the worldwide scale. The long-term monitoring of a population of mosquitoes in southern France has enabled a detailed study to be made of the evolution of resistance genes on a local scale, and has shown that a resistance gene with a lower cost has replaced a former resistance allele with a higher cost.  相似文献   

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A nutrient associated with animal-derived phospholipids has previously been found essential for newly-emerged adults of the mosquito Culex pipiens to fly and survive more than a few days. Pure arachidonic acid was completely effective in supporting the emergence of viable flying adults; in combination with synthetic dipalmitoyl lecithin, which slightly improves larval growth rate without inducing adult flight, it wholly adequately replaces animal phospholipids. Linoleic and linolenic acids, which have satisfied the needs of all insects hitherto shown to require an essential fatty acid, were ineffective for C. pipiens, with or without synthetic lecithin. An optimal effect on adult flight was obtained with 0.05 mg of arachidonic acid per 100 ml of dietary medium, a concentration much lower than the linoleic/linolenic concentrations needed by other insects with an essential fatty acid requirement. The relationship of this unique mosquito fatty acid requirement to the essential fatty acid needs of both vertebrates and insects in general is discussed.  相似文献   

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ABSTRACT. Analysis of video recordings of Culex pipiens quinquefasciatus Say swarms showed that the overall swarming patterns of males and virgin females are similar, even though the short-term characteristics of their flight, such as speed and turning angle, differ. This suggests they have the same response to the visual cue of the swarm 'marker'. The swarming pattern of an individual consists of elliptical loops which, in the short-term, define an area smaller than the swarm as a whole. The foci of these ellipses drift gradually with respect to the marker; individuals do not seem to have preferred positions within the swarm, but drift at random. Male mosquitoes identify and locate females by the sound of their wing-beats. Diffuse sound at the wing-beat frequency of female C.p. quinquefasciatus (500–600 Hz) caused males within the swarm to slow down significantly. Their turning behaviour remained unchanged, so the ellipses decreased in size. The swarm as a whole collapsed into a smaller volume, centred over the marker. Apparently, the response of males to sound consists of at least two parts: initially they alter their flight speed, and then alter their turning behaviour once they have located the source of the sound.  相似文献   

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Rasgon JL 《PloS one》2012,7(3):e30381

Background

Wolbachia are maternally inherited endosymbionts that infect a diverse range of invertebrates, including insects, arachnids, crustaceans and filarial nematodes. Wolbachia are responsible for causing diverse reproductive alterations in their invertebrate hosts that maximize their transmission to the next generation. Evolutionary theory suggests that due to maternal inheritance, Wolbachia should evolve toward mutualism in infected females, but strict maternal inheritance means there is no corresponding force to select for Wolbachia strains that are mutualistic in males.

Methodology/Principal findings

Using cohort life-table analysis, we demonstrate that in the mosquito Culex pipiens (LIN strain), Wolbachia-infected females show no fitness costs due to infection. However, Wolbachia induces up to a 30% reduction in male lifespan.

Conclusions/significance

These results indicate that the Wolbachia infection of the Culex pipiens LIN strain is virulent in a sex-specific manner. Under laboratory situations where mosquitoes generally mate at young ages, Wolbachia strains that reduce male survival could evolve by drift because increased mortality in older males is not a significant selective force.  相似文献   

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ABSTRACT. In both virgin and inseminated female Culex pipiens quinquefasciatus Say, circadian flight-activity has two major components: evening (E) and morning (M) in virgins, and evening (E) and night (N) in inseminated females. These components probably represent the activity of constituent oscillators of the underlying pacemaker system. In DD (constant dark) the E and M peaks are approximately 12 h apart in virgins, the E and N peaks 6–7 h apart in inseminated females. Entrainment to regimes between LD 6:18 and 18:6 appears to have only small effects on the relative position of these components, and after a change to DD they quickly relax towards a common phase-relation. Entrainment to LD 12:12 followed by release into DD or constant dim light (intensities 0.005-5 be) showed that light has a differential effect on the components, initially increasing the period of the E component more than that of the apparently more stable M and N components. Thus with increasing light intensity a bimodal cycle fuses into a unimodal cycle. Light also affected the level of activity, causing big increases in the activity of both virgin and inseminated females at 0.05 lx, but depressing activity, at least initially, at 5 lx. These results indicate that, under natural conditions, moonlight may have big effects, both on the level of activity and on the underlying circadian pacemaker.  相似文献   

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Gene duplication is thought to be the main potential source of material for the evolution of new gene functions. Several models have been proposed for the evolution of new functions through duplication, most based on ancient events (Myr). We provide molecular evidence for the occurrence of several (at least 3) independent duplications of the ace-1 locus in the mosquito Culex pipiens, selected in response to insecticide pressure that probably occurred very recently (<40 years ago). This locus encodes the main target of several insecticides, the acetylcholinesterase. The duplications described consist of 2 alleles of ace-1, 1 susceptible and 1 resistant to insecticide, located on the same chromosome. These events were detected in different parts of the world and probably resulted from distinct mechanisms. We propose that duplications were selected because they reduce the fitness cost associated with the resistant ace-1 allele through the generation of persistent, advantageous heterozygosis. The rate of duplication of ace-1 in C. pipiens is probably underestimated, but seems to be rather high.  相似文献   

19.
AIn the mosquito Culex pipiens (L.) (Diptera: Culicidae) esterases contribute to insecticide resistance by their increased activity. These esterases display a heterogeneous geographical distribution, particularly in Tunisia, where they are very diverse. In this study, we extended the characterization of a highly active esterase first detected in 1996: B12. Esterase B12 displayed the fastest electrophoretic mobility of all the previously described highly active esterases. We showed that it was encoded by the Ester(B12) allele at the Ester locus, and we isolated a strain, TunB12, homozygous for this allele. TunB12 displayed a low (approximately two- to three-fold) but significant resistance to the organophosphates temephos and chlorpyrifos, and to the pyrethroid permethrin. Only temephos resistance was synergized by S,S,S-tributyl-phosphorotrithioate. Real-time quantitative polymerase chain reaction revealed that the Ester(B12) allele was not amplified in TunB12 strain, indicating that B12 high activity could be due to a gene up-regulation mechanism. Ester(B12) allele frequencies also were estimated in 20 Tunisian populations collected in 2005. Analyses revealed a large distribution of this allele all over the country. Finally, sequences of Ester(B12) were acquired and genetic distance trees were constructed with the resistance Ester alleles already published, providing indications about allele's origins. The diverse array of highly active esterases in C. pipiens from Tunisia and the possible scenario of the origin of their coding alleles are discussed in the context of their possible evolution.  相似文献   

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