Transmission of male recombination,segregation distortion and sex-ratio imbalance inDrosophila melanogaster

From the first test cross progenies of control (no larval transfers; no ethyl methanesulphonate), physical stress (two larval transfers; no ethyl methanesulphonate) and 0.75% ethyl methanesulphonate (two larval transfers; 0.75% ethyl methanesulphonate)-treated F₁ (Oregon K +/dumpy black cinnabar, dp b cn) males ofDrosophila melanogaster, respectively, 6,10 and 52 wild-looking first test cross males were again test crossed to obtain second generation. The overall percentages of male recombination detected in the second test cross progenies, in the three sets of experiments, were statistically the same as those in the first test cross progenies. Thus the enhanced male recombination caused by physical stress (with or without ethyl methanesulphonate) was transmitted to next generation. Non-reciprocal male recombination was observed indp b but not inb cn region in both first and second test cross progenies. Three abnormalities, (i) production of wild-type flies in majority overdp b cn type, (ii) Non-Mendelian segregation atdp b andcn loci and (iii) sex-ratio differences fordp bcn and +b cn types observed in test cross progenies of F₁ males ofDrosophila melanogaster were transmitted to next generation when induced with 0.75 % ethyl methanesulphonate but not when these abnormalities were induced with physical stress. The data suggest possible association of non-reciprocal male recombination, segregation distortion and sex-ratio imbalance inDrosophila melanogaster. In fact these may be representing different aspects of the same phenomenon     

Incipient sexual isolation in the nasuta-albomicans complex of Drosophila: mating preference in male-, female- and multiple-choice mating experiments

Interracial divergence is an important facet of speciation. Thenasuta-albomicans complex ofDrosophila with sixteen morphologically identical, karyotypically different but cross-fertile races is an excellent system to study a few dimensions of raciation.Drosophila nasuta nasuta, Drosophila nasuta albomicans, Cytorace 1, Cytorace 2, Cytorace 3 and Cytorace 4 of this subgroup have been subjected to male-, female- and multiple-choice mating experiments. Out of 8456 crosses conducted, 7185 had successful matings. The overall impression is that mating is far from random amongst these six closely related races of thenasuta-albomicans complex. The males ofD. n. albomicans, Cytorace 1 and Cytorace 4 in male-choice, the females of Cytorace 1 and Cytorace 2 in female-choice, and the males and females ofD. n. nasuta, D. n. albomicans, Cytorace 1 and Cytorace 4 against the males and females of Cytorace 2 in multiple-choice experiments, had significantly more homogamic matings than expected. Thus in this study of evolutionary experimentation on raciation under laboratory conditions, we have documented the initiation of preference for con-specific matings among closely related and independently evolving members of thenasuta-albomicans complex ofDrosophila.     

Microscale Laser Surgery Demonstrates the Grasping Function of the Male Sex Combs in Drosophila melanogaster and Drosophila bipectinata

Male secondary sexual traits of animals are richly diversified in form and complexity, yet there are many species in which their precise function remains unknown. Within the genus Drosophila, species belonging to the melanogaster and obscura species groups have evolved a remarkable variety of sex combs, male‐limited secondary sexual traits located on the tarsi of both front legs. Information concerning sex comb function is minimal or absent, except for D. melanogaster, where previous studies indicate that the sex combs are used for grasping the female prior to copulation. These studies, however, do not unambiguously demonstrate comb function, because it has not been possible to ascribe observed behavioral outcomes of the various comb manipulations to changes in the combs per se. We used microscale laser surgery to manipulate comb size in D. melanogaster and D. bipectinata, and tested the hypothesis that the sex combs function as grasping devices in courtship, making them essential for copulation to ensue. Results of high‐resolution behavioral analysis in small observation arenas demonstrated that in both species in which sex combs were surgically eliminated, males were unable to grasp, mount or copulate. The combless foretarsi of these altered males slipped off the end (D. melanogaster) and sides (D. bipectinata) of the female abdomen when courting males attempted to grasp. In most cases, males whose sex combs were reduced but not completely removed exhibited similar copulation probabilities as surgical control males, a result we demonstrated in observation chambers as well as under more ecologically realistic conditions inside population cages where males and females interacted on the surface of fruit substrates. Thus, the sex combs in D. melanogaster and D. bipectinata are grasping devices, essential for mounting and copulation.     

Heat shocks do not mobilize mobile elements in genomes ofDrosophila melanogaster inbred lines

Summary Males of three inbred lines ofDrosophila melanogaster were heat-shocked 90 min at 37°C. The progenies from treated and untreated males mated with untreated females of the same line were checked for their chromosomal insertion patterns of various mobile elements by either in situ hybridization or Southern blots. No modification in the pattern of insertion of the elements studied was observed after heat treatment. Hence, heating males of our inbred lines did not mobilize mobile elements, contrary to recent reports on other lines ofDrosophila melanogaster.     

Reproductive Isolation Among Geographical Populations of <Emphasis Type="Italic">Drosophila Bipectinata</Emphasis> Duda (Diptera,Drosophilidae) with Recognition of Three Subspecies

Among D. bipectinata Duda, 1923, three subspecies, bipectinata from Southeast Asia (SEA) and Okinawa (OKN), szentivanii stat. nov. from Papua New Guinea (PNG) (Mather & Dobzhansky, 1962) and pacificiae ssp. nov. from South Pacific Ocean (SPO), are recognized. The external morphology of the reproductive organs and the numbers of teeth per row in the sex combs are different between the three subspecies. Furthermore, the sterility of hybrid males between strains from the different regions confirms the subspecies status of each population from SEA, PNG and SPO, together with different gene arrangements in the geographical populations. Although males of the strains from OKN (Okinawa), the northernmost population, show significant differences in the number of teeth of sex combs from males of SEA (Southeast Asia) strains, hybrid males between them are fertile.     

Function and genetics of long versus short copulations in the cactophilic fruit fly,drosophila mojavensis (diptera: drosophilidae)

Variation in copulation duration of Drosophila mojavensisstrains was influenced by both sexes. Males maintained predominant control, as copulation duration of pairs from different strains was more similar to that of the strain from which the male was derived, but female origin also contributed significantly to the duration of copulation. Variation among strains was controlled by genes acting additively in both sexes. The size of both males and females also affected copulation duration. Small males copulated longer on average than large males, while males paired with large females copulated longer than those paired with small females. The importance of copulation duration to fitness was tested by correlation analyses with male size, female size, female remating latency, and number of eggs laid prior to female remating. Longer copulations stimulated earlier oviposition, possibly by increasing accessory gland secretions that are passed by males during copulation.     

Age effects on the insemination rate ofAnopheles gambiae s.l. in the laboratory

Age effects on the insemination rate of the Galisua strain ofAnopheles gambiae s.s. (Diptera: Culicidae) and of the Nyanza strain ofAn. arabiensis were investigated in the laboratory. Batches of 7-day old males and females were kept together for 24 h with batches of mosquitoes of the opposite sex of ages ranging from 1–7 days. Males and females were also kept together continuously from emergence. The effect of increasing male/female ratios on the insemination rate was investigated as well. The insemination rate ofAn. arabiensis in the laboratory (96%) was similar to that found in nature, whereas that of our strain ofAn. gambiae s.s. was consistently low (maximum 72%), particularly after females had been together with males for a 24 h period only. The optimum age for insemination was 7 days for males and females of both species. The insemination rate of our strain ofAn. arabiensis was significantly higher at all ages than that of our strain ofAn. gambiae s.s.. The latter strain became inseminated at the earliest when 4 days old. An increase in the male/female ratio significantly enhanced the insemination rate in both strains. It was found that motility of spermatozoa inside the spermatheca, once in contact with saline, could be used as a marker for the approximate time of insemination. It is concluded that the relatively low insemination rate of the Galisua strain ofAn. gambiae s.s. is unlikely to be caused by the rearing conditions. Other factors that may be responsible are discussed.     

Differing amounts of genetic polymorphism in testes and male accessory glands ofDrosophila melanogaster andDrosophila simulans

We surveyed genetic polymorphism by two-dimensional gel electrophoresis of male reproductive tract proteins in 20 isofemale lines each ofDrosophila melanogaster andDrosophila simulans. After classifying 244 such proteins ofDrosophila melanogaster and 271 ofDrosophila simulans by their distribution between testes and accessory glands within the reproductive tract, significant correlations were found between genetic polymorphism and tissue distribution. In both species, gland-specific proteins were significantly more polymorphic than testis-specific proteins, as well as those found in both testes and glands. Simultaneously, inDrosophila simulans, proteins found in roughly equivalent relative abundance in both testes and glands were significantly less variable than gland-specific and testis-specific proteins, as well as those with a quantitative difference in relative abundance between testes and glands. These correlations may reflect general differences in variability between extracellular and intracellular proteins and between proteins with broad as opposed to tissue-specific distributions.We thank the Natural Sciences and Engineering Research Council of Canada for financial support (Grant A0235 to R.S.S.).     

Male recombination with single and homologous P elements in Drosophila melanogaster

It has previously been shown that, in the presence of a source of P element transposase, male recombination in Drosophila melanogaster is induced at a rate of about 1% in the region of a single P[CaSpeR] element. This paper shows that recombinant chromosomes retain unaltered P[CaSpeR] elements at the original site in a high proportion of cases. This result is incompatible with a simple model in which recombination occurs by resolution of a Holliday junction following P element excision and repair. It has also previously been shown that homozygous regions containing a P element produce male recombination levels of 10–20%, an order of magnitude higher than that given by a single element. This paper shows that reciprocal recombinant chromosomes retaining P[CaSpeR] elements can be combined to produce similarly high levels of recombination. This result potentially allows for recombinant chromosomes from homologous recombination to be analysed at the molecular level in the region of the inserted element.     

Estimation of Fine-Scale Recombination Intensity Variation in the <Emphasis Type="Italic">white–echinus</Emphasis> Interval of <Emphasis Type="Italic">D. melanogaster</Emphasis>

Accurate assessment of local recombination rate variation is crucial for understanding the recombination process and for determining the impact of natural selection on linked sites. In Drosophila, local recombination intensity has been estimated primarily by statistical approaches, by estimating the local slope of the relationship between the physical and genetic maps. However, these estimates are limited in resolution and, as a result, the physical scale at which recombination intensity varies in Drosophila is largely unknown. Although there is some evidence suggesting as much as a 40-fold variation in crossover rate at a local scale in D. pseudoobscura, little is known about the fine-scale structure of recombination rate variation in D. melanogaster. Here we experimentally examine the fine-scale distribution of crossover events in a 1.2-Mb region on the D. melanogaster X chromosome using a classic genetic mapping approach. Our results show that crossover frequency is significantly heterogeneous within this region, varying approximately 3.5-fold. Simulations suggest that this degree of heterogeneity is sufficient to affect levels of standing nucleotide diversity, although the magnitude of this effect is small. We recover no statistical association between empirical estimates of nucleotide diversity and recombination intensity, which is likely due to the limited number of loci sampled in our population genetic data set. However, codon bias is significantly negatively correlated with fine-scale recombination intensity estimates, as expected. Our results shed light on the relevant physical scale to consider in evolutionary analyses relating to recombination rate and highlight the motivations to increase the resolution of the recombination map in Drosophila.     

The use of genetic complementation in the study of eukaryotic macromolecular evolution: Rate of spontaneous gene duplication at two loci ofDrosophila melanogaster

Summary Gene duplications must play an important role in the evolutionary development of living organisms. Presented here is a general scheme that uses complementary alleles to isolate gene duplications in diploid organisms. The technique was used inDrosophila melanogaster to assess the rate of spontaneous gene duplication at two loci, maroon-like and rosy. The results indicate (1) that the rate of duplication of the maroon-like locus is on the order of 2.7×10^–6; (2) that the rate of duplication of the rosy locus is approximately 1.7×10^–4; and (3) that duplication occurs in males, suggesting that there may actually be two modes of gene duplication inDrosophila melanogaster.     

A genetic system to detect mitotic recombination between repeated chromosomal sequences in Drosophila Schneider line 2 cells

In order to study mitotic homologous recombination in somatic Drosophila melanogaster cells in vitro and to learn more on the question how recombination is influenced by mutagens, a genetic system was developed where spontaneous and drug-induced recombination could be monitored. Two recombination reporter substrates were stably introduced in multiple copies into the genome of established D. melanogaster Schneider line 2 cells: one plasmid (pSB310) contained the 5′ and 3′ deleted neomycin phosphoribosyltransferase alleles neoL and neoR as direct repeats; the other (pSB485) contained similar deletions (lacZL and lacZR) of the β-galactosidase gene (lacZ). Restoration of a functional neo gene upon mitotic recombination between homologous sequences allowed direct selection for the event, whereas recombination in single cells harbouring the integrated lacZ-based reporter plasmid was detected by histochemical staining or flow cytometric analysis (FACS). The neo-based construct in the clonal transgenic cell line 44CD4 showed a spontaneous recombination frequency of 2.9×10⁻⁴, whereas the 485AD1 cell line harbouring the lacZ-based construct exhibited a frequency of 2.8×10⁻⁴. The alkylating agents EMS and MMS and the clastogen mitomycin C were able to induce recombination in the 485AD1 cell line in a dose-dependent manner. The results obtained from these studies suggest that the transgenic cell lines are potentially useful tools for identifying agents which stimulate direct repeat recombination in somatic Drosophila cells.     

Parasitoid-host relationship betweenTrioxys (Binodoxys) Indicus [Hymenoptera: Aphidiidae] andAphis Craccivora [Hemiptera: Aphididae]. VI. Impact of males on the number of progeny of the parasitoid reared on certain host plants

The present paper elucidates the impact of males on the reproductive rate ofTrioxys (Binodoxys) indicus reared on the aphids ofCajanus cajan, Dolichos lablab andSolanum melongena host plants. The F₁ offspring increases with the increase of parasitoid number. This increase is maximum inC. cajan followed byD. lablab andS. melongena reared aphids. The presence of male parasitoids caused a significant decrease in the emergence of F₁ generation.      

Speciation in Progress? A Continuum of Reproductive Isolation in <Emphasis Type="Italic">Drosophila Bipectinata</Emphasis>

Incipient species in the early stages of divergence can provide crucial information about the genetic basis of reproductive isolation and the evolutionary forces that promote speciation. In this report, we describe two subspecies of Drosophila bipectinata that show a continuum of reproductive isolation. Crosses between strains of the same subspecies produce fully fertile offspring. At the same time, each subspecies harbors extensive variation for the degree of reproductive isolation from the other subspecies. The percentage of fertile hybrid males varies from 0 to 90%, depending on the origin of parental strains, indicating that the genes responsible for hybrid sterility are not fixed within either subspecies, or even within local populations. Reproductive isolation is non-transitive, so that the extent of hybrid sterility depends on the particular combination of strains. The two subspecies show little or no evidence of genetic differentiation at three nuclear loci, suggesting that they diverged very recently or continue to experience significant levels of gene flow. A hybrid zone between the two subspecies may exist in New Guinea and Northeastern Australia.     

Drosophila melanogaster eggshell development: Localization of the s19 chorion gene

Summary Further IF screening ofDrosophila melanogaster geographic strains has revealed a variant of the s19 major chorion protein. Developmental analysis of F1 hybrids indicates that the source of the variation is found in the structural gene for this protein. The linkage group of the variant gene was determined to be the third, and the gene was localized by several methods of recombination analysis. The s19 gene was found to be tightly linked to thesepia locus, as had been previously found for the s18 gene (Yannoni and Petri 1980). Lack of recombination between the s19 and s18 genes in double heterozygotes suggested that these two genes are within 0.3 map units of each other. Although more precise localization of the s19 gene failed, the s18 gene could be more specifically located to the right ofsepia, betweensepia andhairy. Contrary to our prediction (ibid.), the s19 and s18 genes have been found to be tightly linked in spite of the fact that they display somewhat different developmental stage specificity.     

Dynamics of mating success in experimental groups ofDrosophila melanogaster (Diptera: Drosophilidae)

Determinants of male courtship success in Drosophila melanogasterwere examined in groups of five males sequentially presented with five individual females. Thirty-three percent of males never mated, while approximately half of the males mated two or three times. Rapid courtship initiation was associated with male success in early matings only. Male size was important for courtship outcome, but the size distributions of mating and nonmating males and their progeny numbers indicate balancing rather than directional selection on size- dependent courtship success.     

Inbreeding depression and male-mating behavior inDrosophila melanogaster

There have been relatively few studies designed to investigate the effects of inbreeding on behavioral traits. To study this phenomenon, five experimental lines ofDrosophila melanogaster made isogenic for chromosome 2 were evaluated for their male-mating ability and, subsequently, male courtship behavior. All lines showed significant reductions in overall mating ability, and males from all of these lines displayed impaired mating behavior, with two lines displaying particularly aberrant courtship patterns. Line 16 displayed an inability to successfully initiate copulation following successful courtship, while line 17 displayed significant reduction in locomotor activity, resulting in virtually no successful courtship or copulatory activity. The implications of these findings for competitive mating ability in wildDrosophila populations are presented. Further, the importance of mating success as a fitness component in the management of potentially highly inbred populations of endangered species is discussed.     

Genetic instability in mass-rearing colonies of a sex-linked translocation strain of Lucilia cuprina (Wiedemann) (Diptera: Calliphoridae) during a field trial of genetic control

Summary Genetic breakdown occurred in a strain of Lucilia cuprina constructed for the purpose of genetic control of this pest. The strain incorporated autosomal recessive eye colour mutations linked in repulsion with a translocation involving the Y chromosome (male-determining) and two autosomes. In the original strain females had white eyes and males were wild type. The spontaneous breakdown involved a failure of the sex-limited inheritance of the eye colour mutations. Characteristically the frequency of white-eyed males increased rapidly in the strain, whereas the frequencies of the three other phenotypically recognizable breakdown products did not. This suggested that the white-eyed males had a selective advantage over both the wild type males and the other breakdown products. Genetic analysis revealed that recombination, which is normally rare in L. cuprina males, is considerably more frequent in the presence of a Y-autosome translocation, but that recombination alone was insufficient to account for the rate of increase of the white-eyed males in the colony. Genetic and cytological analysis of the breakdown products revealed that reversion of the multi-break translocation also occurred, and that many of the white-eyed males had either only a Y-single-autosome translocation or no translocation at all; thus these males were more fertile than the wild type multi-translocation males. In addition, under colony cage conditions the white-eyed males may have had a behavioural advantage in competition with the wild type males.     

P-related sequences inDrosophila bifasciata: A molecular clue to the understanding of P-element evolution in the genusDrosophila

Summary Two P-elements (bif1 and bif2) were isolated from a genomic library ofDrosophila bifasciata. Both elements are internally deleted and have lost the coding capacity for a functional transposase. One of the elements (bif2) contains an insert consisting of a repetitive sequence. The terminal inverted repeats and the segments necessary for passive mobility are well conserved. Element bif2 has retained rudiments of the coding sequence of exon 0 and exon 3, but the reading frame is destroyed by insertions and deletions. The comparison of theD. bifasciata P-elements with P-elements ofDrosophila melanogaster andDrosophila nebulosa reveals that the two latter sequences are more similar to each other than either of them is to theD. bifasciata elements. This finding contradicts the phylogenetic relationship of the species and can be taken as an indirect but unequivocal evidence for recent horizontal gene transfer from a relative ofD. nebulosa to the gene pool ofD. melanogaster. The P-elements ofD. bifasciata are phylogenetically ancient and have evolved independently for about 50 million years. A higher substitution rate at the third codon position as well as a predominance of conservative replacements at the amino acid level indicates that the P-elements ofD. bifasciata have been under selective constraint over a long period and that immobilization has occurred only recently.     

Investigation of a phage resistantSerratia entomophila strain (BC4B), establishment of generalised transduction and construction ofS. entomophila RecA mutants

ArecA clone was isolated from a cosmid library ofSerratia entomophila constructed in theEscherichia coli strain HB101. Subcloning and transposon mutagenesis were used to identify a 1.36 kb fragment containing therecA gene. A clonedrecA mutation, generated by transposon mutagenesis and the replacement of a portion of therecA gene with an antibiotic resistance cassette, was introduced into the chromosome via a marker exchange technique. TherecA strains created were deficient in DNA repair, homologous recombination and both the spontaneous and UV induction of prophages.S. entomophila recA strains showed continued pathogenicity towards the New Zealand grass grub,Costelytra zealandica. Simple procedures for further construction ofS. entomophila recA strains have been demonstrated.