Vitellogenetic defects in hybrids of the species pair Drosophila virilis and Drosophila texana

In interspecific matings between the species Drosophila virilis and Drosophila texana, female sterility can be observed in F₂ backcross females and in F₂ hybrid females. The results presented in this report show that the female sterility, whenever it exists, is due to prevention of vitellogenin synthesis in the fat body, but other abnormalities such as defects with the hybrid ovaries are not excluded. The observation that sterility appears among females from backcrosses suggests that incompatibilities between interspecific genes may cause female sterility even in the presence of a complete habloid genome from one or the other species. Yet, the parallel observation that female sterility appears only in hybrid females with recombinant chromosomes indicates that sterility results when conspecific combinations of genes on the same chromosome are broken by interspecific recombination. © 1996 Wiley-Liss, Inc.     

The temporal pattern of vitellogenin synthesis in Drosophila grimshawi

The temporal pattern of protein production and, in particular, vitellogenin protein synthesis during the sexual maturation of Drosophila grimshawi females has been studied in vivo by briefly feeding the flies with 35S-methionine and 3H-amino acids. The overall level of incorporation was very low in young flies; it then progressively increased to reach a maximum with the onset of sexual maturity at 13-15 days. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) analyses revealed three classes of proteins: those synthesized throughout the age spectrum, which constitute the majority of protein species; proteins synthesized primarily or only in young flies; and proteins synthesized only by the older flies. In this Drosophila species, the three vitellogenins (V1, V2, and V3) appeared to be synthesized in a two-phase pattern. In the first phase, small quantities of V1 and V2 were detected immunologically in the fat body and hemolymph of newly emerged and 1 day-old flies. These proteins did not accumulate in the hemolymph or the ovaries, apparently being unstable proteins. The second phase commenced in early vitellogenesis (7-9 days of age) with synthesis in the fat body of small quantities of V1 and V2, followed by V3 proteins. These proteins were secreted and accumulated in the hemolymph and 24 h later were found in the ovaries. Their quantities increased rapidly and a steady state of synthesis, release into the hemolymph, and uptake by the ovaries was reached by days 13-15. We have estimated that during the steady state of vitellogenin synthesis, a fly can synthesize in 24 h at least 152 micrograms of vitellogenins, which is more than 2% of its body weight, at an average rate of about 6.3 micrograms vitellogenins/h. About 2 micrograms of this are synthesized in the fat body, and about 4 micrograms in the ovaries. These findings are discussed in terms of their physiological implications and contrasted with the available data on Drosophila melanogaster.     

A novel system of fertility rescue in Drosophila hybrids reveals a link between hybrid lethality and female sterility

Hybrid daughters of crosses between Drosophila melanogaster females and males from the D. simulans species clade are fully viable at low temperature but have agametic ovaries and are thus sterile. We report here that mutations in the D. melanogaster gene Hybrid male rescue (Hmr), along with unidentified polymorphic factors, rescue this agametic phenotype in both D. melanogaster/D. simulans and D. melanogaster/D. mauritiana F(1) female hybrids. These hybrids produced small numbers of progeny in backcrosses, their low fecundity being caused by incomplete rescue of oogenesis as well as by zygotic lethality. F(1) hybrid males from these crosses remained fully sterile. Hmr(+) is the first Drosophila gene shown to cause hybrid female sterility. These results also suggest that, while there is some common genetic basis to hybrid lethality and female sterility in D. melanogaster, hybrid females are more sensitive to fertility defects than to lethality.     

Inferring the evolutionary history of Drosophila americana and Drosophila novamexicana using a multilocus approach and the influence of chromosomal rearrangements in single gene analyses

The evolutionary history of closely related organisms can prove sometimes difficult to infer. Hybridization and incomplete lineage sorting are the main concerns; however, genome rearrangements can also influence the outcome of analyses based on nuclear sequences. In the present study, DNA sequences from 12 nuclear genes, for which the approximate chromosomal locations are known, have been used to estimate the evolutionary history of two forms of Drosophila americana ( Drosophila   americana americana and Drosophila americana texana ) and Drosophila novamexicana ( virilis group of species). The phylogenetic analysis of the combined data set resulted in a phylogeny showing reciprocal monophyly for D. novamexicana and D. americana . Single gene analyses, however, resulted in incongruent phylogenies influenced by chromosomal rearrangements. Genetic differentiation estimates indicated a significant differentiation between the two species for all genes. Within D. americana , however, there is no evidence for differentiation between the chromosomal forms except at genes located near the X/4 fusion and Xc inversion breakpoint. Thus, the specific status of D. americana and D. novamexicana is confirmed, but there is no overall evidence for genetic differentiation between D. a. americana and D. a. texana , not supporting a subspecific status. Based on levels of allele and nucleotide diversity found in the strains used, it is proposed that D. americana has had a stable, large population during the recent past while D. novamexicana has speciated from a peripheral southwestern population having had an ancestral small effective population size. The influence of chromosomal rearrangements in single gene analyses is also examined.     

Interactions between sex-transformation mutants of Drosophila melanogaster. I. Hemolymph vitellogenins and gonad morphology

In Drosophila, vitellogenins (yolk protein precursors) are synthesized by the female fat body, secreted into the hemolymph and subsequently taken up by the developing oocytes. The male fat body, on the other hand, does not do this even when immature ovaries are transplanted into the body cavity and grow. Thus, the hemolymph vitellogenins serve as an easily detectable sexually dimorphic biochemical marker.--We have examined hemolymph vitellogenins by SDS polyacrylamide gel electrophoresis in flies carrying various sex-transformation mutants (dsx, tra, tra-2 and tra-2OTF) singly and in all possible combinations. Chromosomal females homozygous for tra or tra-2 have no detectable hemolymph vitellogenins, while those homozygous for tra-2OTF exhibit appreciable levels of these proteins. Flies homozygous for dsx, both X/X and X/Y, have hemolymph vitellogenins, although the amount is consistently smaller in the latter. Indeed, X/Y; dsx/dsx is the only genotype in which hemolymph vitellogenins are detected in the X/Y flies. A clear hierarchy of epistasis exists among these sex-transformation mutants when they are examined in various combinations: dsx greater than tra, tra-2 greater than tra-2OTF. Moreover, an interaction between tra-2OTF and tra was seen in these experiments: X/X; tra-2OTF/tra-2OTF flies show the presence of only a trace of hemolymph vitellogenins when they are made heterozygous for tra. These results, combined with observations on gonad morphology, are discussed with respect to the Baker and Ridge (1980) hypothesis of sex determination.     

Noncoordinate synthesis of the vitellogenin proteins in tissues of Drosophila grimshawi

In analyzing the in vitro pattern of protein synthesis by the fat body and ovaries of the Hawaiian species Drosophila grimshawi, we have found that the ovaries synthesize much more protein than the female fat body and that the majority of the synthesized proteins are retained by the ovarian tissues. In contrast, the fat body secrets most of the proteins into the culture medium. Vitellogenins are the major class of proteins synthesized and released into the medium by both tissues. The synthesis of the three vitellogenin proteins (V1, V2, V3) is noncoordinate in the two tissues. Ovaries synthesize much more of the V2 protein, less V1 and very little V3, whereas fat body synthesizes more V1 protein with lesser quantities of the other two. The follicle cells were identified as the site of ovarian vitellogenin synthesis in D. grimshawi, confirming the findings in D. melanogaster. In D. grimshawi, the three vitellogenins are synthesized by the follicle cells in a noncoordinate and developmentally regulated manner. V2 and V1 are the predominant proteins at the onset of vitellogenesis (S8-9); their production peaks together with that of V3 a few hours later (S10) and then decreases to quantities equal to that of V3 during early choriogenesis (S11). During active choriogenesis (S12), V2 and V1 cease to be synthesized, but V3 synthesis continues. The vitellogenins synthesized by the follicles in vitro are released into the medium and not incorporated into the oocyte.     

Hybrid Dysgenesis in DROSOPHILA MELANOGASTER: Morphological and Cytological Studies of Ovarian Dysgenesis

A type of intraspecific hybrid sterility, between two strains of Drosophila melanogaster, referred to as GD (gonadal dysgenesis) sterility, is observed when females from a type of strain called M are crossed with males from a second type called P. Absence of egg-laying is characteristic of female GD sterility and its manifestation is conditional on high developmental temperatures. Morphological and cytological studies of GD sterile females are described. These individuals were normal in body size and external appearance. No defects in sperm storage were observed. Both adult and larval ovaries were drastically reduced in size in comparison with control ovaries. This ovarian dysgenesis was sometimes unilateral, but more frequently it was bilateral, particularly in females developing at the highest test temperature. The ovarioles of dysgenic ovaries contained no vitellaria; the germaria lacked any cells resembling the cystocyte clusters of normal ovaries. It is concluded that sterility results from an early blockage in ovarian development, rather than from atrophy of previously developed structures. Possible mechanisms for this developmental arrest are discussed.     

DNA Sequence Variation at the Period Locus Reveals the History of Species and Speciation Events in the Drosophila Virilis Group

The virilis phylad of the Drosophila virilis group consists of five closely related taxa: D. virilis, D. lummei, D. novamexicana, D. americana americana and D. americana texana. DNA sequences from a 2.1-kb pair portion of the period locus were generated in four to eight individuals from each of the five taxa. We found evidence of recombination and high levels of variation within species. We found no evidence of recent natural selection. Surprisingly there was no evidence of divergence between D. a. americana and D. a. texana, and they collectively appear to have had a large historical effective population size. The ranges of these two taxa overlap in a large hybrid zone that has been delineated in the eastern U.S. on the basis of the geographic pattern of a chromosomal fusion. Also surprisingly, D. novamexicana appears to consist of two distinct groups each with low population size and no gene flow between them.     

The evolution of conspecific sperm precedence in Drosophila

Conspecific sperm precedence takes place when females inseminated by both conspecific and heterospecific sperm preferentially produce conspecific rather than hybrid offspring. Although many studies have documented conspecific sperm precedence, most have only identified it between taxa that are already considered to be good species. Here, we test for sperm precedence between two Drosophila pseudoobscura subspecies and between two Drosophila melanogaster races to evaluate how early in evolutionary divergence sperm precedence evolves. We found evidence of weak conspecific sperm precedence between the Drosophila subspecies but none between the Drosophila races. These pairs of taxa are already separated by mating discrimination and/or hybrid sterility, so our observation suggests that conspecific sperm precedence does not always evolve before other barriers to gene exchange.     

Postmating Reproductive isolation between strains of Drosophila willistoni

Speciation can occur through the presence of reproductive isolation barriers that impede mating, restrict cross-fertilization, or render inviable/sterile hybrid progeny. The D. willistoni subgroup is ideally suited for studies of speciation, with examples of both allopatry and sympatry, a range of isolation barriers, and the availability of one species complete genome sequence to facilitate genetic studies of divergence. D. w. willistoni has the largest geographic distribution among members of the Drosophila willistoni subgroup, spanning from Argentina to the southern United States, including the Caribbean islands. A subspecies of D. w. willistoni, D. w. quechua, is geographically separated by the Andes mountain range and has evolved unidirectional sterility, in that only male offspring of D. w. quechua females × D. w. willistoni males are sterile. Whether D. w. willistoni flies residing east of the Andes belong to one or more D. willistoni subspecies remains unresolved. Here we perform fecundity assays and show that F1 hybrid males produced from crosses between different strains found in Central America, North America, and northern Caribbean islands are reproductively isolated from South American and southern Caribbean island strains as a result of unidirectional hybrid male sterility. Our results show the existence of a reproductive isolation barrier between the northern and southern strains and suggest a subdivision of the previously identified D. willistoni willistoni species into 2 new subspecies.     

Insulin signaling is necessary for vitellogenesis in Drosophila melanogaster independent of the roles of juvenile hormone and ecdysteroids: female sterility of the chico1 insulin signaling mutation is autonomous to the ovary

It has been suggested that insulin signaling mutations of Drosophila melanogaster are sterile and long-lived because of juvenile hormone (JH) and ecdysteroid deficiency. However, female sterility of an insulin/IGF-like signaling mutant (chico(1)) of D. melanogaster is not mediated by downstream systemic signaling in terms of major alterations in JH or ecdysteroid levels. chico(1) is a null mutation in the insulin substrate protein (CHICO) gene of D. melanogaster. Homozygous chico(1) females are sterile and their oocytes do not mature beyond the last previtellogenic stage. Homozygous chico(1) females exhibit approximately wild-type rates of JH biosynthesis, ovarian release of ecdysteroids and haemolymph ecdysteroid levels, suggesting that these two major hormone systems play no role in producing the sterility. Previtellogenic wild-type ovaries transplanted into homozygous chico(1) females underwent vitellogenesis, showing that systemic factors present in mutant females are sufficient to support normal vitellogenesis. chico(1) ovaries transplanted into wild-type females did not undergo vitellogenesis indicating that CHICO is necessary in the ovary for vitellogenic maturation. The ovary transplant experiments corroborate the endocrine results and demonstrate that insulin/insulin-like signaling (IIS) is necessary for vitellogenesis even when sufficient levels of JH, ecdysteroids or other factors are present.     

A multilocus microsatellite phylogeny of the Drosophila virilis group

We used a set of 48 polymorphic microsatellites derived from Drosophila virilis to infer phylogenetic relationships in the D. virilis clade. Consistent with previous studies, D. virilis and D. lummei were the most basal species of the group. Within the D. montana phylad, the phylogenetic relationship could not be resolved. Special attention was given to the differentiation between D. americana texana, D. americana americana and D. novamexicana. Significant differences between these three groups were detected by F(ST) analyses. Similarly, a model-based clustering method for multilocus genotype data also provided strong support for the presence of three differentiated groups. This genome-wide differentiation between D. americana texana and D. americana americana contrasts with previous analyses based on DNA sequence data.     

Synthesis of vitellogenic and non-vitellogenic yolk proteins by the fat body and the ovary of Leptinotarsa decemlineata

• 1.1. Isolated ovaries of egg laying females synthesize and secrete three yolk proteins (two vitellogenins and chromoprotein 2).
• 2.2. The contribution of ovarian tissue to total yolk protein production is very small, the major site of synthesis of the three yolk proteins being the fat body.
• 3.3. There is a time lag between yolk protein synthesis by the fat body and yolk protein sequestration by the ovary.
• 4.4. In egg laying females, within 1 hr after the synthesis of both vitellogenins by the fat body, they appear in the oocytes as vitellins.

     

SPERM PRODUCTION AND STERILITY IN HYBRIDS BETWEEN TWO SUBSPECIES OF DROSOPHILA PSEUDOOBSCURA

Subspecies of Drosophila pseudoobscura, one occurring in the United States and the other in Bogota, Columbia, exhibit Haldane's Rule in one direction of the cross. Additionally, D. pseudoobscura produces two sperm types: short, sterile sperm and long, fertile, sperm. Here I examine the relationship between the production of short and long sperm and hybrid sterility. Fertile and sterile hybrid males produce a greater proportion of short sperm compared to parental males with sterile hybrids producing mainly short, immotile sperm. Sperm transfer and storage patterns were similar between fertile hybrid and parental strains; and unexpectedly, short, immotile sperm from sterile hybrids were stored. These findings raise the question of whether different genetic mechanisms disrupt both sperm heteromorphic production and sperm motility and whether this indicates that females exert some control over sperm storage.     

Aggregation pheromones in five taxa of the Drosophila virilis species group

ABSTRACT. Aggregation pheromones have been demonstrated in the closely related taxa: Drosophila americana americana Spencer, D. a. texana Patterson, D. novamexicana Patterson, and D. lummei Hackman. These pheromones function much as has been reported previously for D. virilis Sturtevant. The compounds are produced by sexually mature males, but both sexes respond in a wind-tunnel olfactometer. In all species except D. lummei , a 21-carbon alkene is an important pheromone component. In D. virilis the hydrocarbon is (Z)-10-heneicosene (Z10–21), but in D. a. americana, D. a. texana and D. novamexicana it is (Z)-9-heneicosene (Z9-21). All these taxa respond best to the heneicosene which they produce. D. lummei possesses no heneicosenes but, curiously, responds well to both Z9-21 and Z10-21. All species possess five male-specific esters which were previously discovered in D. virilis : methyl tiglate, ethyl tiglate, isopropyl tiglate, methyl hexanoate and ethyl hexanoate. Ethyl tiglate is the most abundant in each case. Responses to the esters vary among the taxa, ranging from highly significant in D. lummei , particularly to ethyl tiglate, to not demonstrable in D. a. americana. Variability in ester response has also been demonstrated between two strains of D. virilis. In all cases the crude male-derived pheromone is synergistic with an extract of fermented willow bark, on which oviposition is said to occur.     

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.     

Yolk polypeptide secretion and vitelline membrane deposition in a female sterile Drosophila mutant

Ovarian follicle cells of wild type Drosophila melanogaster simultaneously secrete yolk polypeptides (YP1, YP2 and YP3) and vitelline membrane proteins. In order to understand the relationship between these two secretory activities, we have investigated the ultrastructure of a female sterile mutation that alters YP1 secretion and vitelline membrane deposition. Homozygous fs(1)1163 females lay eggs that collapse and contain reduced quantities of YP1. Secretory granules in follicle cells contain an electron-translucent component that is assembled into the developing vitelline membrane in both mutant and wild-type ovaries, and an electron-dense component that disperses after secretion in wild-type ovaries. Mutant ovaries differ from wild-type by (1) having larger secretory granules (2) forming clumps of the dense secretory component within the developing vitelline membrane (3) accumulating more tubules in the cortical ooplasm of vitellogenic oocytes, and (4) possessing altered yolk spheres. Mutant ovaries implanted into wild-type hosts showed no improvement in the secretory granules and slight improvement in the vitelline membrane clumps but amelioration of the oocyte phenotypes. Since genetic evidence suggests that the fs(1)1163 mutation resides in or near the Yp1 gene and biochemical data show that the mutation alters YP1 structure, we conclude that the ultrastructural phenotypes are due to a structurally abnormal YP1 in the mutant. The alteration in vitelline membrane structure caused by the dense clumps could account for collapsed eggs and, hence, the female sterility of the mutant.     

Radiation effects on Drosophila suzukii (Diptera: Drosophilidae) reproductive behaviour

Female remating is a widespread behaviour, reported in several insect species. This behaviour can affect the efficiency of sterile insect technique (SIT); however, little is known about the postcopulatory behaviour of some pest species considered as candidates to be controlled by this technique, such as Drosophila suzukii (Matsumura, 1931) (Diptera: Drosophilidae). In this study, we investigated the effects of male and female sterilization on mating and remating behaviour of D. suzukii. First, we tested the occurrence of multiple mating in different combinations between sterile and fertile males and females. Then, we tested the effects of male and female sterility on female propensity to mate and remate. We found an overall low remating rate by D. suzukii females. Male sterility did not influence mating and remating likelihood; however, copula duration of sterile males was shorter compared to fertile males. On the other hand, sterile females were less likely to mate. Our findings encourage further research regarding the use of SIT to control D. suzukii.     

Characterization of defects in adult germline development and oogenesis of sterile and rescued female hybrids in crosses between Drosophila simulans and Drosophila melanogaster

Crosses between Drosophila melanogaster and D. simulans normally result in progeny that are either inviable or sterile. Recent discovery of strains that rescue these inviability and sterility phenotypes has made it possible to study the developmental basis of reproductive isolation between these two species in greater detail. By producing both rescued and unrescued hybrids and examining the protein product staining patterns of genes known to be involved in early germline development and gametogenesis, we have found that in crosses between D. simulans and D. melanogaster, hybrid female sterility results from the improper control of primordial germline proliferation, germline stem cell maintenance, and cystoblast formation and differentiation during early oogenesis. Rescued hybrid females are fertile, yet they generally have lower amounts of adult germline from the outset and show a premature degeneration of adult germline cells with age. In addition, older rescued hybrid females also exhibit mutant egg phenotypes associated with defects in dorso-ventral patterning which may result from the improper partitioning of cytoplasmic factors during early oogenesis that could stem from the early defect. Although a variety of germline and oogenic defects are described for the hybrid females, all of them can potentially result from the same underlying primary defect. Hybrid males from these same crosses, on the other hand, have no detectable germline in adult reproductive tissues, even when hybrid sterility rescue strains are used, indicating that male sterility and female sterility stem from distinctly different developmental defects.