The nonA gene in Drosophila conveys species-specific behavioral characteristics

The molecular basis of species-specific differences in courtship behavior, a critical factor in preserving species boundaries, is poorly understood. Genetic analysis of all but the most closely related species is usually impossible, given the inviability of hybrids. We have therefore applied interspecific transformation of a single candidate behavioral locus, no-on-transient A (nonA), between Drosophila virilis and D. melanogaster, to investigate whether nonA, like the period gene, might encode species-specific behavioral information. Mutations in nonA can disrupt both visual behavior and the courtship song in D. melanogaster. The lovesong of nonA(diss) mutant males superficially resembles that of D. virilis, a species that diverged from D. melanogaster 40-60 mya. Transformation of the cloned D. virilis nonA gene into D. melanogaster hosts carrying a synthetic deletion of the nonA locus restored normal visual function (the phenotype most sensitive to nonA mutation). However, the courtship song of transformant males showed several features characteristic of the corresponding D. virilis signal, indicating that nonA can act as a reservoir for species-specific information. This candidate gene approach, together with interspecific transformation, can therefore provide a direct avenue to explore potential speciation genes in genetically and molecularly tractable organisms such as Drosophila.     

Association of telomeric regions of salivary gland chromosomes in Drosophila species of the virilis group]

The frequency of participating salivary gland chromosomes in telomeric associations and specific combinations of associated chromosomes were studied in the following species belonging to "virilis" group of Drosophila: D. virilis, D. texana, D. littoralis Sokolov and D. imeretensis Sokolov. In all species studied predominantly telomeres of two chromosomes form an association. In females of the species mentioned the X-chromosome takes part in association twice as frequent as in males. The total length of the chromosome and the presence of subterminal inversions may sometimes influence the frequency of participating the chromosome in associations. However, the data obtained enable to postulate that internal homology of telomeric regions plays the main role in the process. The equal frequency of participating in telomeric associations for definite chromosomes in species studied may resemble the phylogenetic relation of the species.     

Temperature sensitivity of mutations in species of the virillis group of Drosophila. III. The maternal influence and dominance of lethals in D. virillis Sturt. X D. littoralis Sokolov hybrids]

Lethal mutations sensitive to the temperatures 17 and 31 degrees were found in D. virilis. The phenocritical stage for the heat-sensitive mutation begins from the 2nd half of the 3rd larval instar. The specific stage for the cold-sensitive mutation was not found. The mutations are recessive under intraspecific and interspecific (D. littoralis female XD. virilis hermaphrodite) crossing. They are inherited as dominant in the hybrids D. virilis female XD. littoralis hermaphrodite due to the maternal effect of the D. virillis egg cytoplasm.     

Puff expression in relation to genotype]

The studies of genotype influence on puff size in salivary gland chromosomes of Drosophila virilis (stocks 9, 101, 142, 151) and D. texana (the stock 123) reveal significant differences between the species concerning the structure of puff in the 3-C-6 region at the stage of puparium formation. In reciprocal F1 hybrids the size of the puff was intermediate in comparison with parental forms having a slight maternal effect. The differences in puff size in the 5th chromosome between interspecific hybrids and the special stock of D. virilis carrying a region of D. texana 5th chromosome in heterozygous condition (inserted into D. virilis 5the chromosome by double crossing-over) were observed. The transfer of the region of the third chromosome to near centrimetric heterochromatic of the 5th chromosome by translocation resulted in the increase in the 3-B-2 puff size. However, the transposition of the 3-B1 region in the proximal direction with respect to chromocenter did not affect the puff size.     

Cytogenetic localization of Acph-1 and Lap-1 genes in virilis group Drosophila

Gene Acph-1 coding for acid phosphatase was localized on Drosophila virilis chromosome 2 in the region 20A-20E and in D. texana and D. imeretensis homologous regions of the chromosomes 2. Gene Lap-1 coding for leucine aminopeptidase was linked to Acph-1 gene and localized in the 20E-20G region for these Drosophila species. The cytogenetical localization of two genes was determined after analysing recombinant chromosomes by isozymic and cytological methods in the progeny of interspecific hybrids.     

Species-specific differences in tissue-specific expression of alcohol dehydrogenase are under the control of complexcis-acting loci: Evidence fromDrosophila hybrids

Differences in the expression of alcohol dehydrogenase in the hindgut and testis of adult Drosophila virilis, D. texana, D. novamexicana and D. borealis flies were observed. These heritable differences do not arise due to chromosomal rearrangements, since the polytene chromosome banding patterns did not reveal any such gross chromosomal rearrangements near the Adh locus in any of the tested species. Analysis of the interspecific hybrids revealed that these differences are controlled by complex cis-acting genetic loci. Further, the cis-acting locus controlling the expression of ADH in testis was found to be separable by crossing-over.     

Chromosomal rearrangement In(2)TY and linkage maps of the second chromosome of Drosophila virilis

A chromosomal rearrangement In(2)TY, found in a natural population of Drosophila virilis, was examined cytologically, and its genetical characterization was carried out by the use of some marker isozymes and visible marker loci. From the interspecific hybridization between D. virilis and D. americana or D. texana, we deduced that the origin of In(2)TY was from a member of a closely related species of virilis.     

Unusual arrangement of the hsp68 locus in the virilis species group of Drosophila implicates evolutionary loss of an hsp68 gene.

Unlike all other Drosophila species studied to date, species in the virilis group of Drosophila have 2 complete copies of hsp68 arranged in inverted head-to-head orientation. Evidence for this conclusion includes Southern blots for D. virilis, D. lummei, and D. montana, PCR analysis of the former 2 species, in situ hybridization in D. virilis x D. lummei hybrids, and the complete nucleotide sequence of the locus in D. lummei. This organization resembles the primitive state of hsp70 in Diptera. Moreover, the Hsp68 peptide sequence for D. virilis and D. lummei is intermediate between that of Hsp70 and Hsp68 from other Drosophila spp. Therefore, we suggest that the hsp68 locus may have arisen via duplication of the hsp70 locus (or vice versa) early in the history of the genus Drosophila, with 1 hsp68 copy subsequently lost in most other Drosophila species groups.     

Localization of the Dras1 sequence to polytene chromosomes in sibling species of the Drosophila virilis group

Drasl gene was mapped by in situ hybridization to polytene chromosomes of several sibling species of the Drosophila virilis group and hybrids between them. A 1037 bp fragment of the Drasl gene of the D. virilis genome was used as a probe. The gene sequence is localized to the region of the disk 25 A-B on the chromosome 2 of the polytene chromosome map of D. virilis.     

A 9.6 kb intervening sequence in D. virilis rDNA, and sequence homology in rDNA interruptions of diverse species of Drosophila and other diptera.

A large proportion of the 28S ribosomal RNA genes in Drosophila virilis are interrupted by a DNA sequence 9.6 kilobase pairs long. As regards both its presence and its position in the 28S gene (about two thirds of the way in), the D. virilis rDNA intervening sequence is similar to that found in D. melanogaster rDNA, but lengths differ markedly between the two species. Degrees of nucleotide sequence homology have been detected bewteen rDNA interruptions of the two species. This homology extends to putative rDNA intervening sequences in diverse higher diptera (other Drosophila species, the house fly and the flesh fly), but hybridization of cloned D. melanogaster and D. virilis rDNA interruption segments to DNA of several lower diptera has been negative. As is the case with melanogaster rDNA interruptions, segments of the virilis rDNA intervening sequence hybridize with non-rDNA components of the virilis genome, and interspecific homology may involve these non-rDNA sequences as well as rDNA interruptions. There is, however, evidence from buoyant density fractionation of DNA that the distributions of interruption-related sequences are distinct in D. melanogaster and D. virilis genomes. Moreover, thermal denaturation studies have indicated differing extents of homology between hybridizable sequences in D. virilis DNA and different segments of the D. melanogaster rDNA intervening sequence. We infer from our studies that rDNA intervening sequences are prevalent among higher diptera; that in the course of the evolution of these organisms, elements of the intervening sequences have been moderately to highly conserved; and that this conservation extends in at least two distantly related species of Drosophila to similar sequences found elsewhere in the genomes.     

Genetics of esterases in Drosophila of the virilis group. I. Characteristics of esterase patterns in D. virilis,D. texana,D. littoralis,and their hybrids

Starch and polyacrylamide gel electrophoreses have detected six esterase fractions in Drosophila of the virilis group. These esterases have been characterized in detail using a series of substrates and inhibitors and also thermal treatment. Differences in esterase patterns have been found between D. virilis, D. texana, and D. litoralis as well as between D. virilis stocks. An interstock polymorphism for different esterase patterns has been established with respect to the electrophoretic mobilities of a number of esterase fractions. In rare instances, it has been observed within some D. virilis stocks, too. There is specificity in organ distribution of esterase fractions in Drosophila. Monogenic control of the electrophoretic mobilities of esterase-2 and esterase-4 has been demonstrated in D. virilis, and a dimer structure has been found in esterase-2. Genes controlling esterase-2 and esterase-4 are located on the second chromosome (209.3 for esterase-2 and 192.0 for esterase-4). In interstock and interspecific hybrids, esterases usually manifest codominance. In interstock hybrids, esterase-2 forms a hybrid band not observed in interspecific hybrids. In third instar larvae of interspecific hybrids, differential expression of certain esterase isozymes has been noted. These observations are in agreement with data from histochemical studies of organs of different hybrids.     

Satellite Ic: a possible link between the satellite DNAs of D. virilis and D. melanogaster.

In this study, we isolated and characterized a previously undetected cryptic satellite DNA comprising 0.1% of the total nuclear genome of D. virilis. This satellite is hidden from detection in neutral CsCl by satellite I and is therefore designated cryptic satellite I or Ic. Sequence analysis reveals that Ic is the repeating heptanucleotide [poly d(AATATAG): d(CTATATT)]. It is more closely related to the three simple sequence satellite DNAs of D. melanogaster, a distantly related species, than it is to any of the major D. virilis satellite DNA sequences. Ic may therefore be a link between the simple sequence satellites of D. virilis and D. melanogaster. As an extension of this theory, we have constructed a "family tree" linking the satellites of D. virilis and D. melanogaster by a series of "simple" operations. Only one intermediate required by this evolutionary scheme has not yet been identified.     

Conjugation of polytene chromosomes in intraspecies hybrids of the virilis group of Drosophila. II. Hybridization of complementary RNA with polytene chromosomes in specimens]

A cytological hybridization of H-3-complementary RNA synthetized from DNA a template of D. virilis with the polytene chromosomes of D. virilis and the hybrids between D. virilis and D. texana, was carried out in situ. The uridine label of RNA was shown to be located mainly over the disc of the polytene chromosomes, the silver grains in interspecies hybrids being located over both homogous chromosomes including the unpaired gions.     

Interspecific hybridization in Daphnia: distinction and origin of hybrid matrilines

Three coexisting Daphnia species belonging to the D. longispina group (D. galeata, D. hyalina, and D. cucullata) form species-hybrid complexes by producing interspecific hybrids in several lakes in Germany and The Netherlands. To evaluate the genetic consequences of interspecific hybridization, I studied the patterns of mitochondrial DNA (mtDNA) sequence variation. The directionality of interspecific hybridization and divergence of hybrids from parental species was tested, using the DNA sequences of a segment of mtDNA. Via the polymerase chain reaction, it was possible to investigate single animals and even single resting eggs. A species-specific marker was established, using restriction patterns of amplified cytochrome b segments. mtDNA genotypes of hybrids revealed unidirectional mitochondrial gene flow for two hybrids, which were investigated by using multiple clones. No evidence for introgression of mtDNA was found. On the basis of a phylogenetic analysis, the species exhibit considerable distinctness, whereas differences between clones within species and between hybrids and maternal species tend to be very low. These results indicate a recent origin of hybrids and suggest that the radiation of the D. longispina group occurred > 5 Mya.      

Mitochondrial DNA polymorphism in the natural populations of the Drosophila virilis species group

Restriction fragment length polymorphism (RFLP) analysis has been used to evaluate mitochondrial DNA (mtDNA) variation in 12 sibling species forming the Drosophila virilis species group. The variation thresholds corresponding to the interspecific and interstrain levels have been determined. The results indicate that interspecific hybridization has significantly contributed to the evolutionary history of the virilis species group.     

Morphometric analysis of male genitalia in sibling species of Drosophila virilis Sturt

The structure of male genital organs in sibling species of the virilis group of Drosophila was examined using methods of multivariate statistics. The differences among these species were estimated using 33 indices and 2 angle parameters. The intraspecific and interspecific correlation structure of the examined characters and the order of their divergence were established. The key characters with respect to forming interspecific differences in the virilis species group were identified. Based on these results, the relative systematic positions of the sibling species are discussed as well as similarities and differences of the pattern of relationships among the species from that generally accepted for the virilis group.     

The pattern of polytene chromosome synapsis in Drosophila species and interspecific hybrids

The pairing of polytene chromosomes was investigated in Drosophila melanogaster, Drosophila simulans and their hybrids as well as in species of the D. virilis group and in F₁ hybrids between the species of this group. The study of frequency and extent of asynapsis revealed non-random distribution along chromosome arms both in interspecific hybrids and pure Drosophila species. It is suggested that definite chromosome regions exhibiting high pairing frequency serve as initiation sites of synapsis in salivary gland chromosomes.