Male accessory gland secretory protein polymorphism in natural populations of <Emphasis Type="Italic">Drosophila nasuta nasuta</Emphasis> and <Emphasis Type="Italic">Drosophila sulfurigaster neonasuta</Emphasis>

Male accessory gland secretory protein polymorphism was analysed in natural populations of Drosophila nasuta nasuta and D. sulfurigaster neonasuta for the first time, using SDS-PAGE to score polymorphism of these proteins in 2788 individuals of D. n. nasuta and 2232 individuals of D. s. neonasuta from 12 different populations from southern India. A total of 25 and 18 variant protein phenotypes were identified in D. n. nasuta and D. s. neonasuta, respectively. Protein fractions of group III were more polymorphic than those from groups I and II. The results show that accessory gland secretory proteins show high levels of polymorphism, irrespective of species or habitat. Moreover, we have used the variation in the accessory gland proteins to assess the extent of divergence between the species and to infer their population structure. The study suggests that though both D. n. nasuta and D. s. neonasuta belong to the same subgroup, they differ in population structure, as far as accessory gland protein polymorphism is concerned.     

Introgressive hybridization and evolution of a novel protein phenotype: Glue protein profiles in thenasuta-albomicans complex ofDrosophila

Glue proteins are tissue-specific proteins synthesized by larval salivary gland cells ofDrosophila. InDrosophila nasuta nasuta andD. n. albomicans of thenasuta subgroup, the genes that encode the major glue protein fractions are X-linked. In the present study, these X-linked markers have been employed to trace the pattern of introgression ofD. n. nasuta andD. n. albomicans genomes with respect to the major glue protein fractions in their interracial hybrids, called cytoraces. These cytoraces have inherited the chromosomes of both parents and have been maintained in the laboratory for over 400–550 generations. The analysis has revealed that cytoraces withD. n. albomicans X chromosome show eitherD. n. nasuta pattern or a completely novel pattern of glue protein fractions. Further, quantitative analysis also shows lack of correlation between the chromosomal pattern of inheritance and overall quantity of the major glue protein fractions in the cytoraces. Thus, in cytoraces the parental chromosomes are not just differentially represented but there is evidence for introgression even at the gene level.     

Chromosomal analysis and phylogenetic relationships in the Drosophila nasuta subgroup I. Phylogenetic relationships within the Drosophila sulfurigaster species complex

Phylogenetic relationships within the Drosophila sulfurigaster species-complex, which belongs to the D. nasuta subgroup, were investigated on the basis of chromosomal constitution and morphology. D. pulaua is thought to be the most ancestral species, from which D. s. sulfurigaster and D. s. bilimbata derived in one branch and D. s. albostrigata and D. s. neonasuta in another branch.     

Genetic and biochemical analysis of brown eye mutation in Drosophila nasuta nasuta and Drosophila nasuta albomicans

By analyzing the progeny of crosses involving brown eye mutants and the wild types in two members of Drosophila nasuta subgroup namely D. n. nasuta and D. n. albomicans we could show that the mutant gene is recessive, located in the chromosome 2 and the alleles of this gene are present at different loci. A study of fitness in the eye color mutants in comparison with the wild types revealed that D. n. nasuta mutant has higher viability at both 25 ± 1°C and ambient temperatures; while D. n. albomicans mutant has faster rate of development only at 25 ± 1°C. Quantitative analysis of eye pigments in the mutants revealed that there is biosynthesis of both pteridines and xanthommatins unlike in bw/bw of D. melanogaster, where only xanthommatins are synthesized. In both the species, the pteridine quantities in mutants are similar; whereas xanthommatin quantity in is 10 times higher than that of . Further, the F₁ progeny of intraspecific crosses (wild type X mutant) are found to have high amounts of pteridine, even when compared with parental wild type. This revised version was published online in July 2006 with corrections to the Cover Date.     

The chromosomes of two Drosophila races: Drosophila nasuta nasuta and Drosophila nasuta albomicana V. Introgression and the evolution of new karyotypes

Reciprocal crosses were made between an Indian strain of D. n. nasuta (2n=8) and the Thailand strain of D. n. albomicana (2n=6). Hybrids were fertile. They were inbred for over four years. Later, the karyotypes of the hybrid populations were analysed. In the hybrid progeny of the cross between D. n. nasuta females and D. n. albomicana males, there were six types of kaotypes. Of these, only two types had a diploid content of chromosomes. They were males with 2n=7 and females with 2n= 8 , while others were aneuploids. This hybrid population is designated as Cytorace III. On the other hand, hybrid progeny of the reciprocal cross had 2n-8 in both males and females; and there was no karyotypic variation. This hybrid population is named as Cytorace IV. The composition of these new karyotypes of Cytorace III and IV have been presented and compared with those of Cytorace I and II reported by Ramachandra and Ranganath (1986).     

Inversion polymorphism in species of the Drosophila nasuta subgroup from Thailand

Thailand populations of three species of the D. nasuta complex have been analysed for the presence of paracentric inversions. D. albomicans and D. sulfurigaster albostrigata were collected from Phuket, Chiang Mai and the River Kwai, whilst D. kohkoa was found only in Phuket and the River Kwai. Chromosomal polymorphism was studied in respect to geographical distribution. The Phuket populations of all three species proved to be highly polymorphic by comparison with the River Kwai and Chiang Mai populations. The heterozygosity frequencies of inversions were calculated and the variations interpreted as a result of adaptation to local ecogeographical conditions. Shared polymorphisms revealed that D. kohkoa and D. s. albostrigata are more closely related to D. albomicans than they are to each other.Based on a thesis submitted for the degree of Ph.D. in the University of Queensland.     

ON THE ORIGIN OF INCIPIENT REPRODUCTIVE ISOLATION: THE CASE OF DROSOPHILA ALBOMICANS AND D. NASUTA

The nasuta subgroup of Drosophila consists of 12 known species classified within the immigrans group. D. nasuta and D. albomicans are two sibling species widely distributed throughout the Indo-Pacific tropics, which, although morphologically indistinguishable, have different meta-phase-chromosome configurations: chromosomes X and 3 are attached in D. albomicans, so that about 60% of its genes are sex-linked. Our experiments show that, at least in the laboratory, there is no sexual, mechanical, or gametic isolation between the two species. There is, however, hybrid “breakdown” expressed in three ways: 1) reduction in the number of F₂ hybrids produced per culture; 2) reduction in the fertility of F₂ (males) and F₃ (males and females) hybrid progenies; and 3) abnormal sex ratios in the progenies of crosses between strains of certain localities. In experimental populations, the karyotypes of both species are still present in substantial frequencies after 20 generations, although the frequencies of the two karyotypes vary depending on the geographic origin of the strains. Our results support the hypothesis that, in allopatry, the evolution of postzygotic isolation precedes that of prezygotic isolation. The mtDNA is polymorphic in both D. nasuta and D. albomicans and fairly similar between them. Assuming typical rates of mtDNA evolution, the two species would have diverged from each other about 500,000 years ago, whereas the African and Indian populations of D. nasuta (considered to be different subspecies by some authors) might have diverged some 350,000 years ago.     

Inversion polymorphism in populations of Drosophila sulphurigaster albostrigata and Drosophila nasuta albomicans from Phuket,Thailand

Two species of the Drosophila nasuta subgroup of the Drosophila immigrans group, D. sulphurigaster albostrigata and D. nasuta albomicans were investigated in this study. Collections of both species were made from Phuket, Thailand. Both species have similar salivary chromosomes, with four autosomal arms and one sex chromosome arm, and both are highly polymorphic for paracentric inversions. D. s. albostrigata accounted for the majority of the isolines collected and exhibited the greater number of inversions. One inversion, C₁, was common to both species, indicating common ancestry.A non-random distribution of inversions was observed on the proximal end of chromosome II in both D. s. albostrigata and D. n. albomicans. An inter-collection comparison revealed that both rigid and flexible chromosomal polymorphism were operating in the two species, with a seasonal variation noted for one inversion in D. s. albostrigata. A non-random association of two inversions was observed in D. n. albomicans.Based on a comparison of the indices of crossing over, both D. s. albostrigata and D. n. albomicans were found to be more heterozygous than in previous studies, with D. n. albomicans appearing to have evolved further than D. s. albostrigata.Based on a thesis submitted for the degree of Ph. D. at the University of Queensland.     

An allozyme phylogeny of some members of the immigrans species group of Drosophila

Allozyme variations at ten loci, in a few species belonging to four different subgroups of the immigrans species group have been studied. The biochemical phylogeny of these species revealed two main lineages. In one of these main lineages, D. n. nasuta, D. n. albomicans and D. s neonasuta constitute one group while D. immigrans and D. formosana comprise another group. The other main lineage includes D. rubida, D. pararubida, D. hypocausta and D. lineosa.     

Glue proteins inDrosophila nasuta

Larval glue protein fractions ofDrosophila nasuta nasuta were analyzed by sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis. Seven major and at least four minor glue protein fractions were recognized. Six of the major fractions are glycosylated. They migrate as three prominent doublets (>100, 43, and 30/28 kd). The synthesis of traceable amounts of these major fractions begins already during the second as well as during the early stages of the third larval instar. The 43-kd and the 30/28-kd fractions are coded by X-chromosomal genes. They are probably clustered within the huge puff of division 10, which is the most prominent X-chromosomal puff in the polytene chromosomes of the third larval instar. Complex posttranslational modification of all but one major glue protein fraction (14 kd) leads to the formation of about 15 different protein fractions in the final glue product. The amount of glue protein produced byD. n. nasuta larvae (in relation to the total saliva proteins) is nearly twice the amount produced byD. melanogaster larvae (ca. 55 and 32%, respectively). This work was supported by the University Grants Commission, New Delhi, India, the Deutscher Akademischer Austauschdienst, FR Germany (to S.R.R.), and the Deutsche Forschungsgemeinschaft (Ka 309/9-1).     

Taxonomic identification of Drosophila nasuta subgroup strains by glue protein analysis

Protein fractions of salivary glands were analyzed from 30 wildtype strains of eight species belonging to the Drosophila nasuta subgroup by SDS-polyacrylamide gel electrophoresis. The electrophoretic patterns indicated several prominent bands which could be shown to represent the major glue protein fractions. The glue protein fractions are species-specific as well as wildtype strain-specific. Wildtype strain specificities are characterized by variations of the species-specific patterns. The patterns of the different wildtypes, species, and hybrids were used for taxonomic identification within the nasuta subgroup, in which the females are morphologically indistinguishable and the males differ only by the markings of their frons. The hybrids provide evidence for gonosomal as well as autosomal linkage of individual genes coding for the major glue protein fractions.     

Hybridization,transgressive segregation and evolution of new genetic systems in<Emphasis Type="Italic">Drosophila</Emphasis>

Introgressive hybridization facilitates incorporation of genes from one species into the gene pool of another. Studies on long-term effects of introgressive hybridization in animal systems are sparse.Drosophila nasuta (2n = 8) andD. albomicans (2n = 6)—a pair of allopatric, morphologically almost identical, cross-fertile members of thenasuta subgroup of theimmigrans species group-constitute an excellent system to analyse the impact of hybridization followed by transgressive segregation of parental characters in the hybrid progeny. Hybrid populations ofD. nasuta andD. albomicans maintained for over 500 generations in the laboratory constitute new recombinant hybrid genomes, here termed cytoraces. The impact of hybridization, followed by introgression and transgressive segregation, on chromosomal constitution and karyotypes, some fitness parameters, isozymes, components of mating behaviour and mating preference reveals a complex pattern of interracial divergence among parental species and cytoraces. This assemblage of characters in different combinations in a laboratory hybrid zone allows us to study the emergence of new genetic systems. Here, we summarize results from our ongoing studies comparing these hybrid cytoraces with the parental species, and discuss the implications of these findings for our understanding of the evolution of new genetic systems. This paper is dedicated to the memory of our teacher, Prof. N. B. Krishnamurthy.     

Linkage disequilibrium in laboratory populations of Drosophila nasuta

Summary Natural populations of Drosophila nasuta are polymorphic for many gene arrangements. Two non-overlapping inversions of the third chromosome, III-2 and III-35, are most common and display extreme linkage disequilibrium. Six randomly mating laboratory stocks, each founded by one gravid female heterozygous in coupling for both III-2 and III-35, were observed after 32 generations. Significant linkage disequilibrium was observed in all stocks. Recombinants were found in only two stocks. The absence of effective recombination in some stocks and its presence in others might be due to different genotypic backgrounds. We suggest that natural selection, influencing recombination rates in several ways, and intrachromosomal epistasis between the two inversions were the main factors for the maintenance of linkage disequilibrium in D. nasuta.     

Population genetics of Drosophila ananassae: inversion polymorphism and body size in Indian geographical populations

Twelve Indian natural populations of Drosophila ananassae, a cosmopolitan and domestic species, were sampled and laboratory populations (mass cultures) were established from naturally impregnated females. These populations were maintained in the laboratory for some generations and were analysed chromosomally to know the frequency of different inversions. The chromosomal analysis revealed the presence of three cosmopolitan inversions. The data on the whole show that there are significant differences in the frequencies of different chromosome arrangements in these populations. Body size (wing length and thorax length) was measured in both sexes (50 females and 50 males), in all the 12 geographical populations of D. ananassae. There are statistically significant differences in wing length as well as in thorax length of both sexes among different geographical populations. Five geographical strains were crossed reciprocally and body size (wing length and thorax length) was measured in F₁ and F₂ progeny. The comparison of body size (both traits) between mid‐parent, F₁ and F₂ shows that there is an increase in body size in F₁ and F₂ progeny as compared with parents. Thus, there is no break down of heterosis in F₂, which suggests absence of coadaptation in geographical populations of D. ananassae. Scaling test statistical analysis showed additive, dominance and epistatic effects in certain crosses involving geographical strains of D. ananassae. Correlation between chromosome arrangement frequency and body size has also been tested and significant negative correlation has been found between 2L – ST chromosome arrangement and male thorax.     

The chromosomes of two Drosophila races: D. nasuta nasuta and D. n. albomicana

Heterochromatin distribution and differentiation in metaphase chromosomes of two morphologically identical Drosophila races, D. nasuta nasuta and D. n. albomicana, have been studied by C- and N-banding methods. — The total heterochromatin values differ only slightly between these races. However, homologous chromosomes of the two Drosophila forms show striking differences in the size of heterochromatin regions and there is an alternating pattern in D. n. nasuta and D. n. albomicana of chromosomes which contain more, or respectively less heterochromatin than their counterparts in the other race. — Three different N-banding patterns could be obtained depending on the conditions of the method employed: One banding pattern occurs which corresponds to the C-banding pattern. Another pattern is the reverse of the C-band pattern; the euchromatic chromosome regions and the centromeres are stained whereas the pericentric heterochromatin regions remain unstained. In the Y chromosomes of both races and in chromosome 4 of D. n. albomicana, however, the heterochromatin is further differentiated. In the third N-banding pattern only the centromeres are deeply stained. Furthermore, between the races, subtle staining differences in the pericentric heterochromatin regions can be observed as verified in F₁ hybrids. On the basis of C- and N-banding results specific aspects of chromosomal differences between D. n. nasuta and D. n. albomicana are discussed.Dedicated to Prof. W. Beermann on the occasion of his 60th birthday     

Plasmid macro-evolution: selection of deletions during adaptation in a nutrient-limited environment

A study was made of the intra-and inter-population variability of the main traits involved in Trichogramma (T. brassicae and T. cacoeciae) efficiency in host exploitation: longevity, fecundity, progeny viability, progeny sex ratio and progeny allocation. The analysis of isofemale strains shows that differences in progeny viability, progeny sex ratio and progeny allocation are transmissible and relatively stable over two successive generations. Comparison of three strains of T. brassicae originating from different locations, demonstrates differences in fecundity, progeny sex ratio and progeny allocation. Differences in host exploitation strategies also exist between two sympatric populations of T. brassicae and T. cacoeciae. No significant correlation appears between the traits which discriminate populations. The ecological and evolutionary significance and the agronomical importance of the results are discussed.     

SUPPRESSION OF SEX-RATIO MEIOTIC DRIVE AND THE MAINTENANCE OF Y-CHROMOSOME POLYMORPHISM IN DROSOPHILA

Like several other species of Drosophila, D. quinaria is polymorphic for X-chromosome meiotic drive; matings involving males that carry a “sex-ratio” X chromosome (X^SR) result in the production of strongly female-biased offspring sex ratios (Jaenike 1996). A survey of isofemale lines of D. quinaria from several populations reveals that there is genetic variation for partial suppression of this meiotic drive. Crossing experiments show that there is Y-linked, and probably autosomal, variation for suppression of drive. Y-linked suppressors of X-chromosome drive have now been described in several species of Diptera. I develop a simple model for the maintenance of Y-chromosome polymorphism in species polymorphic for X-linked meiotic drive. One interesting feature of this model is that, if there is a stable Y-chromosome polymorphism, then the equilibrium frequency of the standard and sex-ratio X chromosomes is determined solely by Y-chromosome parameters, not by the fitness effects of the different X chromosomes on their carriers. This model suggests that Y-chromosome polymorphism may be easier to maintain than previously thought, and I hypothesize that karyotypic variation in Y chromosomes will be found to be associated with suppression of sex-ratio meiotic drive in other species of Drosophila.     

Retrotransposon‐based genetic diversity of Deschampsia antarctica Desv. from King George Island (Maritime Antarctic)

Deschampsia antarctica Desv. can be found in diverse Antarctic habitats which may vary considerably in terms of environmental conditions and soil properties. As a result, the species is characterized by wide ecotypic variation in terms of both morphological and anatomical traits. The species is a unique example of an organism that can successfully colonize inhospitable regions due to its phenomenal ability to adapt to both the local mosaic of microhabitats and to general climatic fluctuations. For this reason, D. antarctica has been widely investigated in studies analyzing morphophysiological and biochemical responses to various abiotic stresses (frost, drought, salinity, increased UV radiation). However, there is little evidence to indicate whether the observed polymorphism is accompanied by the corresponding genetic variation. In the present study, retrotransposon‐based iPBS markers were used to trace the genetic variation of D. antarctica collected in nine sites of the Arctowski oasis on King George Island (Western Antarctic). The genotyping of 165 individuals from nine populations with seven iPBS primers revealed 125 amplification products, 15 of which (12%) were polymorphic, with an average of 5.6% polymorphic fragments per population. Only one of the polymorphic fragments, observed in population 6, was represented as a private band. The analyzed specimens were characterized by low genetic diversity (uH_e = 0.021, I = 0.030) and high population differentiation (F_ST = 0.4874). An analysis of Fu's F_S statistics and mismatch distribution in most populations (excluding population 2, 6 and 9) revealed demographic/spatial expansion, whereas significant traces of reduction in effective population size were found in three populations (1, 3 and 5). The iPBS markers revealed genetic polymorphism of D. antarctica, which could be attributed to the mobilization of random transposable elements, unique features of reproductive biology, and/or geographic location of the examined populations.     

Satellite DNA of Drosophila nasuta nasuta and D. n. albomicana: Localization in polytene and metaphase chromosomes

The DNA from the two Drosophila nasuta races, D. n. nasuta and D. n. albomicana was investigated by CsCl density gradient centrifugation. D. n. nasuta has one major AT-rich satellite DNA sequence with a density of 1.664g/cm³, while D. n. albomicana has at least three satellites with densities of 1.674g/cm³, 1.665g/cm³ and 1.661 g/cm³. The isolated satellite sequences hybridize in situ to all heterochromatic regions of all metaphase chromosomes of both races. In polytene chromosomes the satellite sequences hybridize exclusively to the chromocenter. All chromosomal regions hybridizing with the satellites show also bright quinacrine fluorescence.     

Sex allocation variation in Daphnia pulex

Daphnia (Crustacea: Cladocera) reproduce by cyclical parthenogenesis in which the sex of offspring is environmentally determined. Although numerous studies have demonstrated that factors such as crowding and short-day photoperiod stimulate male production, there is limited information on variation in allocation to male and female offspring for any species of Daphnia . The present study assessed the presence or absence of male production in 96 isofemale lines (clones) from each of eight populations of Daphnia pulex . An average of 37% (range 18–51%) of clones failed to produce males under crowded conditions in the laboratory. A subset of 14 of these non-male-producing clones also failed to produce males under short-day photoperiod (8L:16D). Three male-producing clones were within-clone mated as well as crossed to three non-male-producing clones to study the inheritance of the failure to produce males. The average frequency of non-male-producing F ₁ progeny was significantly higher (58%, N = 486) among the outcrossed progeny than the inbred progeny (5%, N = 86). In addition, when sixteen of the male-producing outcrossed progeny were within-clone mated, only 7% ( N = 106) of the resulting F ₂ progeny failed to produce males. These results are consistent with a genetic basis for the absence of male production. Average survival of the progeny from the nine outcrossed matings was more than twice (67%) that of the inbred progeny from the three within-clone matings (30%), suggesting that within-clone mating would result in significant inbreeding depression. We present a model that suggests that even low levels of inbreeding could allow non-male-producing females to be maintained in a population. The co-occurrence of non-male-producing females and females that produce both males and females in Daphnia pulex bears a similarity to the gynodioecious breeding system found in some plant species.