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PubMed1976

Comparative field cage tests of the population suppressing efficiency of three genetic control systems for Aedes Aegypti.

Cycling populations of Aedes aegypti were set up in cages and managed in such a way that the populations had a maximum of threefold recovery potential in response to control measures. Into three such populations daily releases were made of males which had been chemosterilised, or were double translocation heterozygotes (T1T3) or T1T3 with sex ration distortion (DT1T3). Eradication of the populations was achieved with all cases, but the rate of suppression was markedly slower with T1T3 than the other two systems, with which the rates were similar. T1T3 and DT1T3 releases introduced considerable inherited genetic loads into the target populations. The results were in general agreement with computer predictions.

Aedes↗
PubMed2004

Genetics of egg production in Drosophila sechellia.

Drosophila sechellia, an island endemic that specializes on a single host plant, has a lower rate of egg production than its generalist sister species D. melanogaster, D. simulans, and D. mauritiana. Earlier work showed that part of this difference in egg production was due to a reduction in the number of ovarioles in D. sechellia relative to its sister species. Here, I extend this earlier work by genetically analyzing the difference in egg production between D. sechellia and D. simulans. In all, 10 genetic markers were used in several interspecific backcrosses to identify chromosome regions that affected the rate of egg production. While previously mapped factors affecting ovariole number appear to impact the rate of egg production, new, non-ovariole factors were also identified. Overall, the difference in egg production between D. sechellia and D. simulans appears to be a polygenic trait. The relationship between these factors and genes involved the adaptation of D. sechellia to its host plant is not yet clear. The data are consistent with the hypothesis that decline in egg production is, in part, a negative pleiotropic effect of genetic changes required for host specialization in D. sechellia, although finer-scale genetic analysis of both traits is needed to truly test this hypothesis.

Animals↗
PubMed2000

Are the same genes responsible for intra- and interspecific variability for sex comb tooth number in Drosophila?

The identification of genes contributing to speciation has the potential to provide important insights into the mechanisms of evolution. One of the most interesting unresolved puzzles is the relationship between intraspecific variability in morphological traits and their interspecific divergence. Intraspecific polymorphisms without major detrimental side-effects may serve as a substrate for selection response during speciation. The same quantitative trait loci (QTLs) may, then, account for the trait variability both within and between species. In contrast, the vast majority of intraspecific variants could be deleterious mutations that have not yet been selected out. In this case intraspecific variation would not ultimately generate interspecific trait differences. In previous work, QTLs responsible for morphological differences between animal species, including those for the secondary sexual trait sex comb tooth number, have been mapped with the resolution of chromosome segments. Here, we mapped QTLs for which alleles segregated between two laboratory lines of Drosophila melanogaster. The two QTLs identified mapped to the X chromosome and accounted for only 8% of the between-line differences, implying that a large number of small-effect genes modify sex combs. One intraspecific QTL mapped to the same interval as the QTL for interspecific differences between D. simulans and D. mauritiana. Whether or not these effects result from the same genes requires further examination.

Animals↗
PubMed2000

Microsatellite analysis indicates genetic differentiation of the neo-sex chromosomes in Drosophila americana americana.

The neo-sex chromosomes of Drosophila americana americana were formed by a centric fusion between the autosomal element B and the X chromosome. Previous work has shown that the neo-Y chromosome is not degenerated genetically and that there is no evidence for genetic differentiation between neo-X and neo-Y chromosomes at the sequence level. To further address the genetic differentiation between the neo-sex chromosomes, microsatellites mapping to the neo-sex chromosome of D. a. americana were isolated. Microsatellite analysis indicated a highly significant differentiation between D. a. americana and D. a. texana as well as between the neo-X and neo-Y chromosomes in D. a. americana. Nevertheless, levels of variability were similar among the neo-sex chromosomes, indicating a very recent origin.

Animals↗
PubMed1999

Metaphase karyotypes and G-banding in sandflies of the Lutzomyia longipalpis complex.

Mitotic metaphase chromosomes (2n = 8) from brain cells of fourth instar sandfly larvae of four geographical strains of the Lutzomyia longipaplis complex were examined microscopically, with bright-field illumination, after staining by a new G-banding technique involving exposure of air-dried chromosome preparations to quinacrine and ultraviolet light. Differences of G-banding and/or position of the centromere on chromosome 4 (the smallest chromosome pair) distinguished four putative sibling species from Costa Rica, Colombia and Brazil (distinctive populations from Jacobina and Lapinha Caves). The karyotype of the population from Jacobina, Brazil, showed an apparently plesiomorphic pattern of G-banding. On the basis of their recognizably different mitotic karyotypes, cytogenetic identification of separate taxa in the L. longipalpis complex should be useful for specific female vector competence and ecology studies.

Animals↗
PubMed2006

Breakpoint structure reveals the unique origin of an interspecific chromosomal inversion (2La) in the Anopheles gambiae complex.

Paracentric chromosomal inversions are major architects of organismal evolution and have been associated with adaptations relevant to malaria transmission in anopheline mosquitoes. The processes responsible for their origin and maintenance, still poorly understood, can be illuminated by analysis of inversion breakpoint sequences. Here, we report the breakpoint structure of chromosomal inversion 2La from the principal malaria vector Anopheles gambiae and its relatives in the A. gambiae complex. The distal and proximal breakpoints of the standard (2L+a) arrangement contain gene duplications: full-length genes and their truncated copies at opposite ends. Intact genes without pseudogene copies in the alternative arrangement (2La) imply that 2L+a is derived and was viable despite damage to genes, because duplication preserved gene function. A unique origin for the interspecific 2La inversion was challenged previously by indirect genetic evidence, but breakpoint sequences determined from members of the A. gambiae complex strongly suggest their descent from a single event. The derived position of 2L+a, long considered ancestral in this medically important group, has significant implications for the phylogenetic history and the evolution of vectorial capacity in the A. gambiae complex.

Animals↗
PubMed2006

Linkage of butterfly mate preference and wing color preference cue at the genomic location of wingless.

Sexual isolation is a critical form of reproductive isolation in the early stages of animal speciation, yet little is known about the genetic basis of divergent mate preferences and preference cues in young species. Heliconius butterflies, well known for their diversity of wing color patterns, mate assortatively as a result of divergence in male preference for wing patterns. Here we show that the specific cue used by Heliconius cydno and Heliconius pachinus males to recognize conspecific females is the color of patches on the wings. In addition, male mate preference segregates with forewing color in hybrids, indicating a genetic association between the loci responsible for preference and preference cue. Quantitative trait locus mapping places a preference locus coincident with the locus that determines forewing color, which itself is perfectly linked to the wing patterning candidate gene, wingless. Furthermore, yellow-colored males of the polymorphic race H. cydno alithea prefer to court yellow females, indicating that wing color and color preference are controlled by loci that are located in an inversion or are pleiotropic effects of a single locus. Tight genetic associations between preference and preference cue, although rare, make divergence and speciation particularly likely because the effects of natural and sexual selection on one trait are transferred to the other, leading to the coordinated evolution of mate recognition. This effect of linkage on divergence is especially important in Heliconius because differentiation of wing color patterns in the genus has been driven and maintained by natural selection for Müllerian mimicry.

Animals↗
PubMed1977

Cytogenetic observations on translocations in species A of the Anopheles gambiae complex.

The ovarian polytene chromosomes of females of species A of the Anopheles gambiae complex, from colonies suspected of containing heterozygous translocations, were examined. In three lines, the presence of translocations was confirmed and the chromosomes involved in the interchanges identified. The usefulness of cytogenetic methods for the detection of translocations is discussed.

Animals↗
PubMed1965

CHROMOSOME VELOCITY DURING MITOSIS AS A FUNCTION OF CHROMOSOME SIZE AND POSITION.

Chromosome velocity has been studied in living Melanoplus differentialis spermatocytes by phase contrast cinemicrography. Melanoplus chromosomes (and bivalents) differ in length by as much as 1:3.5. As expected, no size-dependent velocity differences were detected in anaphase, and this is also shown to be true for the less predictable movements during prometaphase congression. The size of the X chromosome can change during observation following x-irradiation, but this is equally without influence on velocity. However, an effect of position on velocity is found in both prometaphase and in anaphase: the chromosomes furthest from the central interpolar axis move 25 per cent faster than more central chromosomes. A simple mechanical model relating frictional resistance and mitotic forces to chromosome velocity is discussed in detail. Calculations from the model suggest that a significant difference in the force acting on a large, as compared with a small chromosome is necessary to account for the observed similarity in velocity. Therefore, it is concluded that the mitotic forces are so organized or regulated that velocity is, within limits, independent of load. The implications of velocity-load independence in relation to the molecular origin of mitotic forces are discussed.

Anaphase↗
PubMed2006

Multilocus test for introgression between the cactophilic species Drosophila mojavensis and Drosophila arizonae.

Information obtained from laboratory studies regarding the efficacy of barriers to gene flow (reproductive isolation) between species is often incomplete or misleading, so detailed genetic analyses are needed to determine whether hybridization and introgression occur in nature. Previous laboratory studies of the cactophilic species Drosophila mojavensis and Drosophila arizonae suggest that reproductive isolation is incomplete and that gene flow may occur in sympatry. We sampled 18 nuclear and one mitochondrial loci from multiple populations of D. arizonae and D. mojavensis to test for the signature of recent or historic gene flow between these two species. We located chromosomal regions that were inverted between these species and analyzed those regions independently of others. Statistical tests for introgression using all loci or only collinear loci failed to reject expectations of an isolation model. Further tests using average nucleotide differences between species and phylogenetic analyses also failed to find support for introgression between D. mojavensis and D. arizonae. Additional ecological and behavioral studies of these species in their natural habitats are required to explain why the signature of gene flow was not detected at the DNA sequence level in populations when laboratory studies suggest such gene flow should be possible.

Animals↗
PubMed1996

Genotypic and phenotypic characterization of the Drosophila melanogaster olfactory mutation Indifferent.

Two Drosophila melanogaster third chromosomes carrying the EMS-induced mutations IndifferentA (IndfA) and IndifferentB (IndfB), previously isolated from larvae showing an anosmia when stimulated with nonanol, were recombined with a multi-marked chromosome in order to localize the mutant character(s). Recombinant strains were tested for their larval olfactory responses and classed as either mutant or wild type; both Indf characters were found to be located on the right arm of the chromosome, between ebony and claret. Deletion mapping suggests that the Indifferent wild-type character is a haplo-insufficiency and that IndfA and IndfB are located in cytological region 96A2-7. Deficiencies and both mutant strains were tested with 14 closely related odors (alcohols, acetates, acids and methyl esters, between eight and 10 carbons long). When stimulated with methyl octanoate, IndfA and IndfB appeared recessive; noncomplementation was observed for this phenotype in IndfA/IndfB hybrids indicating that the two characters are allelic. The overall responses of IndfA, IndfB and the deficiencies indicate that Indf is involved in processing organic odors of between eight and 10 carbons in length.

Animals↗
PubMed1998

A screen to identify Drosophila genes required for integrin-mediated adhesion.

Drosophila integrins have essential adhesive roles during development, including adhesion between the two wing surfaces. Most position-specific integrin mutations cause lethality, and clones of homozygous mutant cells in the wing do not adhere to the apposing surface, causing blisters. We have used FLP-FRT induced mitotic recombination to generate clones of randomly induced mutations in the F1 generation and screened for mutations that cause wing blisters. This phenotype is highly selective, since only 14 lethal complementation groups were identified in screens of the five major chromosome arms. Of the loci identified, 3 are PS integrin genes, 2 are blistered and bloated, and the remaining 9 appear to be newly characterized loci. All 11 nonintegrin loci are required on both sides of the wing, in contrast to integrin alpha subunit genes. Mutations in 8 loci only disrupt adhesion in the wing, similar to integrin mutations, while mutations in the 3 other loci cause additional wing defects. Mutations in 4 loci, like the strongest integrin mutations, cause a "tail-up" embryonic lethal phenotype, and mutant alleles of 1 of these loci strongly enhance an integrin mutation. Thus several of these loci are good candidates for genes encoding cytoplasmic proteins required for integrin function.

Alleles↗
PubMedDate not supplied

Genetic dissection of honeybee (Apis mellifera L.) foraging behavior.

We demonstrate the effects of a new quantitative trait locus (QTL), designated pln3, that was mapped in a backcross population derived from strains of bees selected for the amount of pollen they store in combs. We independently confirmed pln3 by demonstrating its effects on individual foraging behavior, as we did previously for QTLs pln1 and pln2 (Hunt et al. 1995). QTL pln2 is very robust in its effects on foraging behavior. In this study, pln2 was again shown to affect individual foraging behavior of workers derived from a hybrid backcross of the selected strains. In addition, pln2 was shown to affect the amount of pollen stored in combs of colonies derived from a wide cross of European and Africanized honeybees. This is noteworthy because it demonstrates that we can map QTLs for behavior in interstrain crosses derived from selective breeding and study their effects in unselected, natural populations. The results we present also demonstrate the repeatability of finding QTLs with measurable effects, even after outcrossing selected strains, suggesting that there is a relatively small subset of QTLs with major effects segregating in the population from which we selected our founding breeding populations. The different QTLs, pln1, pln2, and pln3, appear to have different effects, revealing the complex genetic architecture of honeybee foraging behavior.

Animals↗
PubMed2001

An investigation of the cause of low variability on the fourth chromosome of Drosophila melanogaster.

The fourth chromosome of Drosophila melanogaster lacks meiotic recombination. There is also a lack of nucleotide variation on the chromosome. This lack of variation could have been caused by a recent selective sweep, by background selection, or by a combination of these two forces. It should be possible to differentiate between the two mechanisms by studying the frequencies of polymorphic sites on the chromosome: a selective sweep should have resulted in low-frequency polymorphisms, whereas higher frequency polymorphisms would indicate the action of background selection. We have analyzed retrotransposable element insertions on the fourth chromosome in 11 strains of D. melanogaster. The polymorphisms found have a range of frequencies, with the presence of some insertions with high frequencies suggesting that the lack of variation is the result of background selection. We summarize the data using two statistics: the number of sites shared by more than one of the sample of 11 chromosomes (internal sites) and the mean number of transposable element differences in presence or absence between the sampled chromosomes. Simulations indicate that a selective sweep occurring more than 15,000 (0.03N) generations ago cannot be ruled out from the number of internal sites, although the number of differences between the chromosomes suggests either background selection or a sweep occurring more than 60,000 (0.12N) generations ago. Our results show no homoplasies and are thus consistent with no recombination occurring on the chromosome. The difficulties of distinguishing between the models using polymorphism data are discussed.

Animals↗
PubMed1997

Expression and suppression of circulative aphid transmission in pea enation mosaic virus.

Pea enation mosaic virus (PEMV) is composed of two autonomously replicating virus RNAs related to the genomic RNAs of viruses in the genera Luteovirus and Umbravirus. The transmission of PEMV resembles that of its luteovirus relatives in utilizing circulative aphid transmission. However, unlike its luteovirus counterparts, PEMV can also be mechanically transmitted. Prolonged mechanical passage of PEMV can lead to the loss of aphid transmissibility, a trait that is mirrored by specific changes in the PEMV virion composition. These changes were used to examine the virus contribution to vector transmission and the mechanisms by which it is regulated. Using a local lesion isolation technique, one aphid transmissible and two aphid non-transmissible isolates of PEMV were compared. Structural analysis of a 54 kDa minor structural subunit unique to the aphid transmissible isolate demonstrated that it was a fusion of the 21 kDa virus coat protein and a 33 kDa protein encoded immediately downstream of the 21 kDa ORF, consistent with the formation of the 54 kDa subunit by translational readthrough. Genetic analyses utilizing exchanges between infectious in vitro transcripts of each isolate demonstrated that although the 33 kDa protein was non-essential for infection, its presence was mandatory for aphid transmission, and that specific changes within the 33 kDa ORF were sufficient to confer or abolish aphid transmission. This study also demonstrates that isolates of PEMV exist as mixtures of aphid transmissible and non-transmissible genotypes, and provides insight into the mechanisms used by this virus to down-regulate aphid transmission in response to a specific selection pressure.

Amino Acid Sequence↗
PubMed1992

Identification of members of the Simulium ochraceum species complex in the three onchocerciasis foci in Mexico.

Larval collections of Simulium ochraceum Walker (Diptera: Simuliidae) were made in a variety of streams in the three onchocerciasis foci in Mexico and identified by cytotaxonomic criteria, based on the banding pattern of polytene chromosomes in larval salivary gland nucleii. S. ochraceum cytotype A was found in the Soconusco focus, cytotype B in the Oaxaca focus and cytotype C (not previously recorded in Mexico) in the Chamula focus. Attempts to analyse chromosomes of adult specimens were unsuccessful. A preliminary study of the cuticular hydrocarbons of adult specimens by gas liquid chromatography provided evidence that this technique may be suitable for separating the cytotypes.

Animals↗