Hiroshi Matsubayashi

A locus for female discrimination behavior causing sexual isolation in Drosophila

The genetic basis of sexual isolation that contributes to speciation is one of the unsolved questions in evolutionary biology. Drosophila ananassae and Drosophila pallidosa are closely related, and postmating isolation has not developed between them. However, females of both species discriminate their mating partners, and this discrimination contributes to strong sexual isolation between them. By using surgical treatments, we demonstrate that male courtship songs play a dominant role in female mate discrimination. The absence of the song of D. pallidosa dramatically increased interspecies mating with D. ananassae females but reduced intraspecies mating with D. pallidosa females. Furthermore, genetic analysis and chromosomal introgression by repeated backcrosses to D. pallidosa males identified possible loci that control female discrimination in each species. These loci were mapped on distinct positions near the Delta locus on the middle of the left arm of the second chromosome. Because the mate discrimination we studied is well developed and is the only known mechanism that prevents gene flow between them, these loci may have played crucial roles in the evolution of reproductive isolation, and therefore, in the speciation process between these two species.

Heterospecific inter-pulse intervals of courtship song elicit female rejection in Drosophila biauraria

Abstract The present study investigated the significance of song in sexual isolation in Drosophila biauraria . Interspecific copulation was not observed with a heterospecific D. triauraria male that had intact wings, although it was often observed when the males wings were removed, indicating that heterospecific courtship song elicits female rejection, and prevents copulation. Artificially synthesized songs were played to a female with a wingless, antennaless male. The conspecific inter-pulse interval of artificial song increased mating frequency, whereas the heterospecific, longer or shorter, inter-pulse interval significantly decreased the frequency. The mating frequency with random noise and silence showed intermediate values. Female rejection behaviour was greater with heterospecific than with conspecific inter-pulse intervals of artificial song; with random song and silence female responses were intermediate. This indicates that the inter-pulse interval is used as a species discriminator in D. biauraria females. It is suggested that the females ability to discriminate inter-pulse intervals and her responses, rejection and acceptance, have evolved under the influence of reinforcement, reproductive character displacement, or both, which triggered sexual selection.

Retrovirus-like features and site specific insertions of a transposable element, tom, in Drosophila ananassae

SummaryThe tom element, putatively associated with optic morphology (Om) mutations in Drosophila ananassae, was identified as a retrovirus-like transposable element. The tom element was found to terminate with 475 (or 474) base pair direct repeats which are identical in sequence to each other. Southern blot and heteroduplex analyses showed the tom element to have high homology to 297 and 17.6, two retrotransposons found in D. melanogaster. As in the cases of 297 and 17.6, tom includes nucleotide sequences coding for a presumptive protease and reverse transcriptase, similar in amino acid sequence to those of the Moloney murine leukaemia virus. At the tom insertion site of the sn9g locus, a host DNA sequence (T)ATAT was found to be duplicated on each side of the tom insertion and all other tom elements examined were also flanked by (T)ATAT. In each of six cases, the 5′ flanking host sequence was TATAT. These results indicate that the target sequence of the tom element may be TATAT and that the entire region or a part of this sequence was duplicated on insertion of the tom element.

(Z,Z)-5,27-Tritriacontadiene: Major sex pheromone ofDrosophila pallidosa (Diptera; Drosophilidae)

A crude cuticular extract from both sexes of 3660 fruit flies (Drosophila pallidosa) was subjected to SiO2 and AgNO3/SiO2 column chromatography, accompanied by bioassay for the sex pheromone activity. After three chromatographic steps, the active fraction was obtained. The main component of the active fraction was determined to be (Z,Z)-5,27-tritriacontadiene [(Z,Z)-5,27-C33:2, on the basis of gas-liquid chromatographic analysis, chemical derivatization and gas chromatography-mass spectrometry. Synthetic (Z,Z)-5,27-C33:2 at 5 female equivalents (FE) elicited a clear courtship response with a high courtship index amongD. pallidosa males. Therefore it was concluded that (Z,Z)-5,27-C33:2 was a major sex pheromone component in this species.

TARGETED EXPRESSION OF IP3 SPONGE AND IP3 DSRNA IMPAIRES SUGAR TASTE SENSATION IN DROSOPHILA

We evaluated the role of IP3 in sugar taste reception in Drosophila melanogaster by inactivating the IP3 signaling using genetic tools. We used the “IP3 sponge,” composed of the modified ligand-binding domain from the mouse IP3 receptor, which was designed to absorb IP3 in competition with native IP3 receptors. Another tool was a transgene that generates double-stranded RNA against IP3 receptor mRNA. Both inhibitors diminished the sensitivity of flies to trehalose and sucrose, as estimated by behavioral assays and electrophysiological recordings from the sugar receptor cells. The result indicates that IP3 signaling is indispensable for sugar reception in Drosophila.

Courtship behavior and sexual isolation between Drosophila auraria and D. triauraria in darkness and light

Sexual isolation between two species of the Drosophila auraria complex, D. auraria and D. triauraria is different in darkness and light. In darkness there is complete isolation while in light it is only partial. The sensory bases of these differences were investigated by behavioral studies in darkness and light. In darkness there was no normal courtship sequence but males of both species displayed attempted copulation to homospecific and heterospecific females, as well as homospecific males. After a few hours together, homospecific copulations were observed after females displayed a characteristic posture: spreading the wings. Such an acceptance posture, also observed in other Drosophila species, was probably released by the wing vibration of a homospecific male. In light, visual signals alone are able to elicit males orientation and following, whether flies are housed together or physically separated. Intense homosexual courtships were observed. All these data suggest that males have a low discrimination ability and females play the main role in sexual isolation.

Genetic analysis of Drosophila virilis sex pheromone: genetic mapping of the locus producing Z-(11)-pentacosene.

Z-(11)-pentacosene, Drosophila virilis sex pheromone, is predominant among the female cuticular hydrocarbons and can elicit male courtship behaviours. To evaluate the genetic basis of its production, interspecific crosses between D. novamexicana and genetically marked D. virilis were made and hydrocarbon profiles of their backcross progeny were analysed. The production of Z-(11)-pentacosene was autosomally controlled and was recessive. Of the six D. virilis chromosomes only the second and the third chromosomes showed significant contributions to sex pheromone production, and acted additively. Analysis of recombinant females indicated that the locus on the second chromosome mapped to the proximity of position 2-218.

Effects of Courtship Song in Interspecific Crosses Among the Species of the Drosophila auraria Complex (Diptera: Drosophilidae)

The courtship behavior and the effects of courtship song in inter- and intraspecific crosses were studied in the four sympatric species of the Drosophila auraria complex: D. auraria, D. biauraria, D. subauraria, and D. triauraria. Orientation, tapping, and vibration (the repertoires of male courtship) were observed in both inter- and intraspecific crosses, suggesting that signals from heterospecific females were enough to elicit such male behaviors. The crossability tests with wingless or winged heterospecific males (tests for wing effects) revealed that winged heterospecific males copulated less than wingless ones in all four species but not all the pairwise cases. Since the crossability tests with aristaless females (deaf) or normal females showed essentially the same results as the tests for wing effects, we concluded that the sound produced by wing vibration plays an important role and that the wing movement itself is less important. These findings suggest that courtship songs are of great importance in mate discrimination and the sexual isolation between the species of this complex.

Molecular and histological characterizations of the Om(2D) mutants in Drosophila ananassae.

SummaryA series of transposon-induced optic morphology (Om) mutants found in a hypermutable marker stock of Drosophila ananassae provides a useful system for analyzing the molecular mechanism of eye morphogenesis. In the present study, one of the 25 Om loci so far reported, Om(2D), has been subjected to histological and molecular analyses as a first step toward understanding the role of Om genes in eye morphogenesis. Histological abnormalities observed during eye morphogenesis of the mutant, i.e. cell death within the eye-antennal discs of third instar larvae, and loss of the lamina, disorganized ommatidia and atrophied optic lobes in adults, were all comparable to those reported with various eye morphology mutants of D. melanogaster. Approximately 25 kb of genomic DNA including the Om(2D) locus was cloned by tom tagging. Southern blot and cloning analyses of two alleles of the Om(2D) locus revealed that insertions of the tom element occurred at three sites within 359 bp; two tandemly arrayed toms sharing one long terminal repeat at the junction and an internally deleted tom were present 359 by apart from each other in Om(2D)63, while a single tom in reverse orientation was present within the 359 by in Om (2D)10a. Host DNA sequences at the three insertion sites were TATAT or AATAT, and ATAT was duplicated upon the tom insertion. Three spontaneous revertants and one induced extreme derivative of Om(2D)63 were obtained and characterized. A complete revertant lost all the preexisting tom elements. Two partial revertants lost one or two of the preexisting tom elements. In the extreme derivative, an additional insertion sequence was found within the two tandem tom elements. Northern blot analysis showed two transcription units in the Om (2D) region: one was on the centromere side of the tom insertion site and expressed a 3.2 kb major RNA and several minor RNAs; the other resided on the telomere side of the tom insertion and expressed a 1.5 kb RNA. Both 3.2 kb and 1.5 kb transcripts were expressed throughout development, but the former was more abundant in mutant embryos and the latter more highly expressed in mutant third instar larvae than in the corresponding stages in wild type.

Excitatory and inhibitory control of mating activity inDrosophila auraria andbiauraria by light

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