Comparative analysis of cuticular hydrocarbons in the Drosophila virilis species group

• 1.1. Chemical structures were determined for the cuticular alkanes, alkenes, and certain of the alkadienes for 11 D. virilis group species.
• 2.2. Male-specific hydrocarbons occurred in five species: these were 9-heneicosene in D. americana and D. novamexicana, 10-heneicosene in D. virilis, 5,13- and 5,15-pentacosadienes in D. kanekoi, and 9-pentacosene in one strain of D. lummei.
• 3.3. Hydrocarbon profiles of newly emerged flies always differed from mature files.
• 4.4. Relationships among the species, with respect to hydrocarbon profiles, were investigated by cluster analysis.

     

Cuticular hydrocarbons as contact sex pheromone in the parasitoid Dibrachys cavus

Cuticular hydrocarbons (CHCs) cover the cuticle of virtually any insect and do not only protect them from desiccation, but also possess various communicative functions. Previous studies suggested a function as contact sex pheromones in the parasitic wasp family Pteromalidae, but further species need to be studied before more general conclusions are possible. Here, we demonstrate a contact sex pheromone in females of Dibrachys cavus (Walker) (Hymenoptera: Pteromalidae). Males of this parasitoid were arrested on cadavers of 1‐ to 2‐day‐old females, but neither on newly emerged females nor on males. Extracts from 1‐ to 2‐day‐old females and non‐polar fractions were also behaviorally active suggesting a non‐polar contact sex pheromone. Chemical analyses of bioactive and non‐active CHC profiles by gas chromatography–mass spectrometry and subsequent principal component analysis (PCA) revealed that the bioactive profiles from 1‐ to 2‐day‐old females were clearly distinguishable from all other profiles. Among the chemicals showing the strongest impact in the PCA were the two 3‐methylalkanes 3‐methylnonacosane and 3‐methylhentriacontane, which were absent or trace components in the inactive profiles and whose relative amounts increased in females when they became sexually attractive. The putative function of 3‐methylalkanes as key components of the contact sex pheromones in Pteromalidae is discussed.     

Cuticular hydrocarbons of triatomines

Triatomine insects (Hemiptera) are the vectors of Chagas disease. Their cuticular surface is covered by a thin layer of lipids, mainly hydrocarbons, wax esters, fatty alcohols, and free or esterified fatty acids. These lipids play a major role in preventing a lethal desiccation, altering the absorption of chemicals and microorganism penetration, they also participate in chemical communication events. Lipid components are biosynthetically related, the synthesis of long chain and very long chain fatty acids was first shown in the integument of Triatoma infestans through the concerted action of fatty acid synthases (FAS's) and fatty acyl-CoA elongases. A final decarboxylation step produces the corresponding hydrocarbon. Capillary gas chromatography coupled to mass spectrometry analyses showed that cuticular hydrocarbons of Triatominae comprise saturated straight and methyl-branched chains, from 18 to more than 43 carbon atoms. Odd-chain hydrocarbons, mostly from 27 to 33 carbons, are the major straight chains. Different isomers of mono, di, tri, and tetramethylcomponents, mostly from 29 to 39 atoms in the carbon skeleton, account for the major methyl-branched hydrocarbons. The presence, absence, and relative quantities of these hydrocarbons represent characters for their chemical phenotype, and are useful for differentiating genera, species and populations. In this review, we will discuss the metabolic pathways involved in hydrocarbon formation, and their structure, together with their role in insect survival. We will also review the utility of cuticular hydrocarbon fingerprints in chemotaxonomy.     

Invasion of Drosophila virilis by the Penelope transposable element

The Penelope family of transposable elements (TEs) is broadly distributed in most species of the virilis species group of Drosophila. This element plays a pivotal role in hybrid dysgenesis in Drosophila virilis, in which at least four additional TE families are also activated. Here we present evidence that the Penelope family of elements has recently invaded D. virilis. This evidence includes: (1) a patchy geographical distribution, (2) genomic locations mainly restricted to euchromatic chromosome arms in various geographical strains, and (3) a high level of nucleotide similarity among members of the family. Two samples from a Tashkent (Middle Asia) population of D. virilis provide further support for the invasion hypothesis. The 1968 Tashkent strain is free of Penelope sequences, but all individuals collected from a 1997 population carry at least five Penelope copies. Furthermore, a second TE, Ulysses, has amplified and spread in this population. These results provide evidence for the Penelope invasion of a D. virilis natural population and the mobilization of unrelated resident transposons following the invasion.     

Drosophila Cuticular Hydrocarbons Revisited: Mating Status Alters Cuticular Profiles

Most living organisms use pheromones for inter-individual communication. In Drosophila melanogaster flies, several pheromones perceived either by contact/at a short distance (cuticular hydrocarbons, CHs), or at a longer distance (cis-vaccenyl acetate, cVA), affect courtship and mating behaviours. However, it has not previously been possible to precisely identify all potential pheromonal compounds and simultaneously monitor their variation on a time scale. To overcome this limitation, we combined Solid Phase Micro-Extraction with gas-chromatography coupled with mass-spectrometry. This allowed us (i) to identify 59 cuticular compounds, including 17 new CHs; (ii) to precisely quantify the amount of each compound that could be detected by another fly, and (iii) to measure the variation of these substances as a function of aging and mating. Sex-specific variation appeared with age, while mating affected cuticular compounds in both sexes with three possible patterns: variation was (i) reciprocal in the two sexes, suggesting a passive mechanical transfer during mating, (ii) parallel in both sexes, such as for cVA which strikingly appeared during mating, or (iii) unilateral, presumably as a result of sexual interaction. We provide a complete reassessment of all Drosophila CHs and suggest that the chemical conversation between male and female flies is far more complex than is generally accepted. We conclude that focusing on individual compounds will not provide a satisfactory understanding of the evolution and function of chemical communication in Drosophila.     

Composition and sex attractancy of cuticular hydrocarbons from houseflies: Effects of age,sex, and mating

Analysis of cuticular hydrocarbons from mated and unmated male houseflies, Musca domestica, indicated that only minor changes in composition occurred during the post-eclosion period. In contrast, female hydrocarbon composition changed considerably during the post-eclosion period and was affected by age, mating, and sexual maturation. The cuticular hydrocarbons from sexually mature female houseflies, both mated and unmated, were attractive to male houseflies. Hydrocarbons from unmated male houseflies were not attractive to male houseflies. Hydrocarbons from males held to maturity with females were somewhat attractive to males, probably as a result of physical transfer of the attractant from the females.     

Cytological and linkage maps of Drosophila virilis chromosomes

Cytological (photographic) maps of third-instar larvae Drosophila virilis salivary gland chromosomes were constructed; genetic maps of the chromosomes are also given together with the list of mutations known for this species.     

Signals of demographic expansion in Drosophila virilis

Background

The antagonistic co-evolution of hosts and their parasites is considered to be a potential driving force in maintaining host genetic variation including sexual reproduction and recombination. The examination of this hypothesis calls for information about the genetic basis of host-parasite interactions – such as how many genes are involved, how big an effect these genes have and whether there is epistasis between loci. We here examine the genetic architecture of quantitative resistance in animal and plant hosts by concatenating published studies that have identified quantitative trait loci (QTL) for host resistance in animals and plants.

Results

Collectively, these studies show that host resistance is affected by few loci. We particularly show that additional epistatic interactions, especially between loci on different chromosomes, explain a majority of the effects. Furthermore, we find that when experiments are repeated using different host or parasite genotypes under otherwise identical conditions, the underlying genetic architecture of host resistance can vary dramatically – that is, involves different QTLs and epistatic interactions. QTLs and epistatic loci vary much less when host and parasite types remain the same but experiments are repeated in different environments.

Conclusion

This pattern of variability of the genetic architecture is predicted by strong interactions between genotypes and corroborates the prevalence of varying host-parasite combinations over varying environmental conditions. Moreover, epistasis is a major determinant of phenotypic variance for host resistance. Because epistasis seems to occur predominantly between, rather than within, chromosomes, segregation and chromosome number rather than recombination via cross-over should be the major elements affecting adaptive change in host resistance.     

Drosophila virilis has long and highly polymorphic microsatellites

Comparative genomics is a powerful approach to inference of the dynamics of genome evolution. Most information about the evolution of microsatellites in the genus Drosophila has been obtained from Drosophila melanogaster. For comparison, we collected microsatellite data for the distantly related species Drosophila virilis. Screening about 0.5 Mb of nonredundant genomic sequence from GenBank, we identified 239 dinucleotide microsatellites. On average, D. virilis dinucleotides were significantly longer than D. melanogaster microsatellites (7.69 repeats vs. 6.75 repeats). Similarly, direct cloning of microsatellites resulted in a higher mean repeat number in D. virilis than in D. melanogaster (12.7 repeats vs. 12.2 repeats). Characterization of 11 microsatellite loci mapping to division 40-49 on the fourth chromosome of D. virilis indicated that D. virilis microsatellites are more variable than those of D. melanogaster.     

Comparison of the gap segmentation gene hunchback between Drosophila melanogaster and Drosophila virilis reveals novel modes of evolutionary change.

We have cloned and sequenced a large portion of the hunchback (hb) locus from Drosophila virilis. Comparison with the Drosophila melanogaster hb sequence shows multiple strong homologies in the upstream and downstream regions of the gene, including most of the known functional parts. The coding sequence is highly conserved within the presumptive DNA-binding finger regions, but more diverged outside of them. The regions of high divergence are correlated with regions which are rich in short direct repeats (regions of high 'cryptic simplicity'), suggesting a significant influence of slippage-like mechanisms in the evolutionary divergence of the two genes. Staining of early D.virilis embryos with an hb antibody reveals conserved and divergent features of the spatial expression pattern at blastoderm stage. It appears that the basic expression pattern, which serves as the gap gene function of hb, is conserved, while certain secondary expression patterns, which have separate functions for the segmentation process, are partly diverged. Thus, both slippage driven mutations in the coding region, which are likely to occur at higher rates than point mutations and the evolutionary divergence of secondary expression patterns may contribute to the evolution of regulatory genes.     

Cuticular hydrocarbons of Chagas disease vectors in Mexico

Capillary gas-liquid chromatography was used to analyse the cuticular hydrocarbons of three triatomine species, Triatoma dimidiata, T. barberi and Dipetalogaster maxima, domestic vectors of Chagas disease in Mexico. Mixtures of saturated hydrocarbons of straight and methyl-branched chains were characteristic of the three species, but quantitatively different. Major methylbranched components mostly corresponded to different saturated isomers of monomethyl, dimethyl and trimethyl branched hydrocarbons ranging from 29 to 39 carbon backbones. Sex-dependent, quantitative differences in certain hydrocarbons were apparent in T. dimidiata.