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Quantitative genetics aims at untangling the genetic and environmental effects on phenotypic variation. Trait heritability, which summarizes the relative importance of genetic effects, is estimated at the intraspecific level, but theory predicts that heritability could influence long-term evolution of quantitative traits. The phylogenetic signal concept bears resemblance to heritability and it has often been called species-level heritability. Under certain conditions, such as trait neutrality or contribution to phylogenesis, within-species heritability and between-species phylogenetic signal should be correlated. Here, we investigate the potential relationship between these two concepts by examining the evolution of multiple morphological traits for which heritability has been estimated in Drosophila melanogaster. Specifically, we analysed 42 morphological traits in both sexes on a phylogeny inferred from 22 nuclear genes for nine species of the melanogaster subgroup. We used Pagel's λ as a measurement of phylogenetic signal because it is the least influenced by the number of analysed taxa. Pigmentation traits showed the strongest concordance with the phylogeny, but no correlation was found between phylogenetic signal and heritability estimates mined from the literature. We obtained data for multiple climatic variables inferred from the geographical distribution of each species. Phylogenetic regression of quantitative traits on climatic variables showed a significantly positive correlation with heritability. Convergent selection, the response to which depends on the trait heritability, may have led to the null association between phylogenetic signal and heritability for morphological traits in Drosophila. We discuss the possible causes of discrepancy between both statistics and caution against their confusion in evolutionary biology., (© 2022. The Author(s), under exclusive licence to Springer Nature Switzerland AG.)

The intragenomic distribution of five retrotransposon families (297, 1731, copia, mdg1 and roo) in the species of the melanogaster complex was studied by comparing results of the Southern blotting technique in males and females with those of in situ hybridization. The degree of structural polymorphism of each family in the different species was also investigated by restriction enzyme analysis. It was found that genomic distribution is a trait that depends on the family and species. The distribution of roo is mainly euchromatic in the four species and 1731 is heterochromatic, but the distribution of families 297, copia and mdg1 is markedly different in the melanogaster and simulans clades. These families were mainly euchromatic in D. melanogaster but heterochromatic in its sibling species. In the simulans clade most copia and mdg1 elements are located on chromosome Y. Differences in genomic distribution are unrelated with structural conservation. The relation of intragenomic distribution to phylogeny, transpositional activity and the role of the host genome are discussed.

Horizontal transfer in Drosophila has been inferred for several families of transposable elements. Specifically, the retroelement roo has been suggested to have been horizontally transferred between the species D. melanogaster, D. simulans, D. sechellia and D. yakuba. The inferences were based on the observation that divergence between transposable elements in different species was lower than the divergence found in typical nuclear genes and in the incongruence of phylogenies of the species and their TEs. Here, we address the question of the possible horizontal transfer of roo between species of the Drosophila genus by studying the presence absence of a duplication of 99 bp in the 5'UTR of the transposon, as well as comparing the sequences of the paralogous and orthologous duplicated repeats within and between species. First, the repeats were only found in five species of the melanogaster subgroup. Second, the date of occurrence of the duplication event originating the repeats was posterior to the split of the subgroup. The duplication date suggests an origin previous to the split of D. simulans and D. sechellia and close to the divergence of D. melanogaster from the D. simulans complex. These data point to horizontal transfer to the afrotropical species D. yakuba and D. erecta from one of the cosmopolitan species D. melanogaster or D. simulans. We propose that the parasitoid wasp Leptopilina could have been the vector of horizontal transfer after the observation that a sequence of 845 bp with high homology to a fragment of roo was isolated from this wasp. [ABSTRACT FROM AUTHOR]

The Zygothrica genus group of Drosophilidae encompasses more than 437 species and five genera. Although knowledge regarding its diversity has increased, uncertainties about its monophyly and position within Drosophilidae remain. Genomic approaches have been widely used to address different phylogenetic questions and analyses involving the mitogenome have revealed a cost-efficient tool to these studies. Thus, this work aims to characterize mitogenomes of three species of the Zygothrica genus group (from the Hirtodrosophila, Paraliodrosophila and Zygothrica genera), while comparing them with orthologous sequences from other 23 Drosophilidae species and addressing their phylogenetic position. General content concerning gene order and overlap, nucleotide composition, start and stop codon, codon usage and tRNA structures were compared, and phylogenetic trees were constructed under different datasets. The complete mitogenomes characterized for H. subflavohalterata affinis H002 and P. antennta present the PanCrustacea gene order with 22 transfer RNA (tRNA) genes, two ribosomal RNA (rRNA) genes, 13 protein coding genes and an A+T rich region with two T-stretched elements. Some peculiarities such as the almost complete overlap of genes tRNAH/ND4, tRNAF/ND5 and tRNAS2/ND1 are reported for different Drosophilidae species. Non-canonical secondary structures were encountered for tRNAS1 and tRNAY, revealing patterns that apply at different phylogenetic scales. According to the best depiction of the mitogenomes evolutionary history, the three Neotropical species of the Zygothrica genus group encompass a monophyletic lineage sister to Zaprionus, composing with this genus a clade that is sister to the Drosophila subgenus., (© 2021. The Author(s), under exclusive licence to Springer Nature Switzerland AG.)

This paper reports genome sizes of one Hawaiian Scaptomyza and 16 endemic Hawaiian Drosophila species that include five members of the antopocerus species group, one member of the modified mouthpart group, and ten members of the picture wing clade. Genome size expansions have occurred independently multiple times among Hawaiian Drosophila lineages, and have resulted in an over 2.3-fold range of genome sizes among species, with the largest observed in Drosophila cyrtoloma (1C = 0.41 pg). We find evidence that these repeated genome size expansions were likely driven by the addition of significant amounts of heterochromatin and satellite DNA. For example, our data reveal that the addition of seven heterochromatic chromosome arms to the ancestral haploid karyotype, and a remarkable proportion of ~70 % satellite DNA, account for the greatly expanded size of the D. cyrtoloma genome. Moreover, the genomes of 13/17 Hawaiian picture wing species are composed of substantial proportions (22-70 %) of detectable satellites (all but one of which are AT-rich). Our results suggest that in this tightly knit group of recently evolved species, genomes have expanded, in large part, via evolutionary amplifications of satellite DNA sequences in centric and pericentric domains (especially of the X and dot chromosomes), which have resulted in longer acrocentric chromosomes or metacentrics with an added heterochromatic chromosome arm. We discuss possible evolutionary mechanisms that may have shaped these patterns, including rapid fixation of novel expanded genomes during founder-effect speciation. [ABSTRACT FROM AUTHOR]

Heterochromatin plays an important role in the spatial arrangement and evolution of the eukaryotic genetic apparatus. The closely related species Drosophila virilis (phyla virilis) and D. kanekoi (phyla montana) differ in the amount of heterochromatin along the chromosomes as well as by the presence of the metacentric chromosome 2, which emerged as a result of a pericentric inversion during speciation, in the D. kanekoi karyotype. The purpose of this study was to establish if chromosome rearrangements have any influence on the linear redistribution of centromeric heterochromatin in polytene chromosomes and the spatial organization of chromosomes in the nuclei of nurse cell. We have microdissected the chromocenter of D. virilis salivary gland polytene chromosomes; obtained a DNA library of this region (DvirIII); and hybridized (FISH) DvirIII to the salivary gland and nurse cell polytene chromosomes of D. virilis and D. kanekoi. We demonstrated that DvirIII localizes to the pericentromeric heterochromatin regions of all chromosomes and peritelomeric region of chromosome 5 in both species. Unlike D. virilis, the DvirIII signal in D. kanekoi chromosomes is detectable in the telomeric region of chromosome 2. We have also conducted a 3D FISH of DvirIII probe to the D. virilis and D. kanekoi nurse cell chromosomes. In particular, the DvirIII signal in D. virilis was observed in the local chromocenter at one pole of the nucleus, while the signal belonging to the telomeric region of chromosome 5 was detectable at the other pole. In contrast, in D. kanekoi there exist two separate DvirIII-positive regions. One of these regions belongs to the pericentromeric region of chromosome 2 and the other, to pericentromeric regions of the remaining chromosomes. These results suggest that chromosome rearrangements play an important role in the redistribution of heterochromatin DNA sequences in the genome, representing a speciation mechanism, which, in general, could also affect the chromosome orientation in the 3D nuclear space. [ABSTRACT FROM AUTHOR]

Detailed chromosome photomaps are the first step to develop further chromosomal analysis to study the evolution of the genetic architecture in any set of species, considering that chromosomal rearrangements, such as inversions, are common features of genome evolution. In this report, we analyzed inversion polymorphisms in 25 different populations belonging to six neotropical species in the cardini group: Drosophila cardini, D. cardinoides, D. neocardini, D. neomorpha, D. parthenogenetica and D. polymorpha. Furthermore, we present the first reference photomaps for the Neotropical D. cardini and D. parthenogenetica and improved photomaps for D. cardinoides, D. neocardini and D. polymorpha. We found 19 new inversions for these species. An exhaustive pairwise comparison of the polytene chromosomes was conducted for the six species in order to understand evolutionary patterns of their chromosomes. [ABSTRACT FROM AUTHOR]

Comparative genomics in Drosophila began in 1940, when Muller stated that the ancestral haploid karyotype of this genus is constituted by five acrocentric chromosomes and one dot chromosome, named A to F elements. In some species of the willistoni group such as Drosophila willistoni and D. insularis, the F element, instead of a dot chromosome, has been incorporated into the E element, forming chromosome III (E + F fusion). The aim of this study was to investigate the scope of the E + F fusion in the willistoni group, evaluating six other species. Fluorescent in situ hybridization was used to locate two genes of the F element previously studied- cubitus interruptus ( ci) and eyeless ( ey)-in species of the willistoni and bocainensis subgroups. Moreover, polytene chromosome photomaps corresponding to the F element (basal portion of chromosome III) were constructed for each species studied. In D. willistoni, D. paulistorum and D. equinoxialis, the ci gene was located in subSectction 78B and the ey gene in 78C. In D. tropicalis, ci was located in subSection 76B and ey in 76C. In species of the bocainensis subgroup, ci and ey were localized, respectively, at subsections 76B and 76C in D. nebulosa and D. capricorni, and 76A and 76C in D. fumipennis. Despite the differences in the subsection numbers, all species showed the same position for ci and ey. The results confirm the synteny of E + F fusion in willistoni and bocainensis subgroups, and allow estimating the occurrence of this event at 15 Mya, at least. [ABSTRACT FROM AUTHOR]

The hAT transposons, very abundant in all kingdoms, have a common evolutionary origin probably predating the plant-fungi-animal divergence. In this paper we present their general characteristics. Members of this superfamily belong to Class II transposable elements. hAT elements share transposase, short terminal inverted repeats and eight base-pairs duplication of genomic target. We focus on hAT elements in Drosophila, especially hobo. Its distribution, dynamics and impact on genome restructuring in laboratory strains as well as in natural populations are reported. Finally, the evolutionary history of hAT elements, their domestication and use as transgenic tools are discussed. [ABSTRACT FROM AUTHOR]

Trypsin participates in many fundamental biological processes, the most notably in digesting food. The 12 species of Drosophila provide a great opportunity to analyze the duplication pattern of trypsins and their association with dietary changes. Here, we find that the trypsin family expands dramatically after speciation. The duplication events are strongly related to the host preferences, with significantly more copy numbers in species breeding on rotting fruits. Temporal analysis of the duplication events indicates that the occurrences of these events are not simultaneous, but rather correlate to the ecological change or host shift. Furthermore, we find that the specialists and generalists have different adaptive selections, which is revealed by dynamic duplication and/or deletion and relatively high Ka/Ks values on the duplicated events in specialists. Our findings suggest that the duplication of trypsin genes has played an important role in the adaption of Drosophila to the diverse ecosystems. [ABSTRACT FROM AUTHOR]

The degree and pattern of sexual isolation among closely related species can be utilized for predicting the direction of evolution and deriving a phylogeny. The Drosophila bipectinata species complex is a group of four morphologically very similar species, belonging to the ananassae subgroup of the melanogaster species group. Sexual isolation among the members of this complex was studied by employing the male-choice technique. To test the difference between the homogamic and heterogamic matings, chi-square values were calculated under the assumption of random mating and the degree of sexual isolation was measured by estimating isolation index. To test the difference in proportions of heterogamic matings between reciprocal crosses, normal deviate (z) was calculated. The direction of evolution among these species has been discussed in the light of models proposed by different workers. Our results suggest that while D. bipectinata, Drosophila parabipectinata and Drosophila malerkotliana are closely related to each other, D. pseudoananassae is distantly related to these three species. The species pairs D. bipectinata and D. parabipectinata and D. parabipectinata and D. malerkotliana show asymmetrical sexual isolation. Based on this, it is suggested that D. bipectinata and D. malerkotliana share a common ancestor where as D. parabipectinata has been derived from D. bipectinata. Their phylogenetic relationship has been discussed in the light of phylogenies suggested by earlier workers. [ABSTRACT FROM AUTHOR]

We have conducted a structure and functional analysis of the hobo transposable element of Drosophila melanogaster. A minimum of 141 bp of the left (L) end and 65 bp of the right (R) end of the hobo were shown to contain sequences sufficient for transposition. Both ends of hobo contain multiple copies of the motifs GGGTG and GTGGC and we show that the frequency of hobo transposition increases as a function of the copy number of these motifs. The R end of hobo contains a unique 12 bp internal inverted repeat that is identical to the hobo terminal inverted repeats. We show that this internal inverted repeat suppresses transposition activity in a hobo element containing an intact L end and only 475 bp of the R end. In addition to establishing cis-sequences requirements for transposition, we analyzed trans-sequence effects of the hobo transposase. We show a hobo transposase lacking the first 49 amino acids catalyzed hobo transposition at a higher frequency than the full-length transposase suggesting that, similar to the related Ac transposase, residues at the amino end of the transposase reduce transposition. Finally, we compared target site sequences of hobo with those of the related Hermes element and found both transposons have strong preferences for the same insertion sites. [ABSTRACT FROM AUTHOR]

Drosophila sechellia is closely related to the cosmopolitan and widespread model species, D. simulans. This species, endemic to the Seychelles archipelago, is specialized on the fruits of Morinda citrifolia, and harbours the lowest overall genetic diversity compared to other species of Drosophila. This low diversity is associated with a small population size. In addition, no obvious population structure has been evidenced so far across islands of the Seychelles archipelago. Here, a microsatellite panel of 17 loci in ten populations from nine islands of the Seychelles was used to assess the effect of the D. sechellia's fragmented distribution on the fine-scale population genetic structure, the migration pattern, as well as on the demography of the species. Contrary to previous results, also based on microsatellites, no evidence for population contraction in D. sechellia was found. The results confirm previous studies based on gene sequence polymorphism that showed a long-term stable population size for this species. Interestingly, a pattern of Isolation By Distance which had not been described yet in D. sechellia was found, with evidence of first-generation migrants between some neighbouring islands. Bayesian structuring algorithm results were consistent with a split of D. sechellia into two main groups of populations: Silhouette/Mahé versus all the other islands. Thus, microsatellites suggest that variability in D. sechellia is most likely explained by local genetic exchanges between neighbouring islands that have recently resulted in slight differentiation of the two largest island populations from all the others. [ABSTRACT FROM AUTHOR]

Biological variation exists across a nested set of hierarchical levels from nucleotides within genes to populations within species to lineages within the tree of life. How selection acts across this hierarchy is a long-standing question in evolutionary biology. Recent studies have suggested that genome size is influenced largely by the balance of selection, mutation and drift in lineages with different population sizes. Here we use population cage and maternal transmission experiments to identify the relative strength of selection at an individual and cytoplasmic level. No significant trends were observed in the frequency of large (L) and small (S) mtDNAs across 14 generations in population cages. In all replicate cages, new length variants were observed in heteroplasmic states indicating that spontaneous length mutations occurred in these experimental populations. Heteroplasmic flies carrying L genomes were more frequent than those carrying S genomes suggesting an asymmetric mutation dynamic from larger to smaller mtDNAs. Mother-offspring transmission of heteroplasmy showed that the L mtDNA increased in frequency within flies both between and within generations despite sampling drift of the same intensity as occurred in population cages. These results suggest that selection for mtDNA size is stronger at the cytoplasmic than at the organismal level. The fixation of novel mtDNAs within and between species requires a transient intracellular heteroplasmic stage. The balance of population genetic forces at the cytoplasmic and individual levels governs the units of selection on mtDNA, and has implications for evolutionary inference as well as for the effects of mtDNA mutations on fitness, disease and aging. [ABSTRACT FROM AUTHOR]

Sequence differentiation has been widely studied between populations and species, whereas interest in expression divergence is relatively recent. Using microarrays, we compared four geographically distinct populations of Drosophila simulans and a population of Drosophila sechellia, and interspecific hybrids . We observed few differences between populations, suggesting a slight population structure in D. simulans. This structure was observed in direct population comparisons, as well as in interspecific comparisons (hybrids vs. parents, D. sechellia vs. D. simulans). Expression variance is higher in the French and Zimbabwean populations than in the populations from the ancestral range of D. simulans (Kenya and Seychelles). This suggests a large scale phenomenon of decanalization following the invasion of a new environment. Comparing D. simulans and D. sechellia, we revealed 304 consistently differentially expressed genes, with striking overrepresentation of genes of the cytochrome P450 family, which could be related to their role in detoxification as well as in hormone regulation. We also revealed differences in genes involved in Juvenile hormone and Dopamine differentiation. We finally observed very few differentially expressed genes between hybrids and parental populations, with an overrepresentation of X-linked genes. [ABSTRACT FROM AUTHOR]

The mechanisms of speciation that appear in the early stages of reproductive isolation has been of recent interest to evolutionary biologists. Experiments were conducted to study behavioral isolation between karyotypically different homozygous strains derived from natural populations of Drosophila ananassae. Three mass cultures stocks established from flies collected from natural populations were employed and homozygous stocks (ST/ST and AL/AL) were made through selection for homozygosity. By employing male-choice technique, mating success was scored by direct observation in the Elens-Wattiaux mating chamber. There is preference for homogamic matings in all the three populations and the differences between homogamic and heterogamic matings are statistically significant in two populations (Lucknow and Varanasi). These findings provide evidence that there is incipient sexual isolation between karyotypically different strains of D. ananassae derived from natural populations which shows that chromosome arrangements may affect the mate recognition system in D. ananassae. [ABSTRACT FROM AUTHOR]

Abstract  The morphology of male genitalia whilst stable within species, exhibits huge interspecific variation. This variation is likely to be as a result of sexual selection due to the direct involvement of these reproductive structures in mating and sperm transfer. In contrast, internal soft tissue components of the genitalia are generally poorly investigated as they are not directly involved in physical and mechanical adequacy during sperm transfer. However, these soft tissue structures may also drive differential male–female interactions, particularly in internally fertilising organisms where females have the ability to store sperm and bias male reproductive success. In this paper we use the drosophila model to investigate the role of male and female reproductive elements in sexual selection. Our meta-analysis supplemented with additional new data clearly shows that within species, sperm length versus testis length, and sperm length versus seminal receptacle length, are highly correlated. Thus, independent of the phylogenetic relationship among species, gamete evolution is likely to result in sexual selection interactions that drive the evolution of internal reproductive components in both sexes. Our results and discussion of the literature highlight the importance of considering internal soft structures that may influence fertilisation, when investigating selective forces acting on the evolution of reproductive traits. [ABSTRACT FROM AUTHOR]

Abstract  It is commonly recognized that speciation does not necessarily imply extensive variation between populations, and what the speciation process per se consists of still remains an unanswered question. We advocate here that the variation of male terminalia does not necessarily result in noticeable reproductive isolation. We report whether there is invariance or variance of traits central to sexual selection processes (i.e. male terminalia and sperm length) compared to traits which are generally assumed to vary more neutrally (i.e. allozymes) in the strictly Afrotropical forest-dwelling continental species Drosophila teissieri. Three geographic blocks can be recognized along the present range of the species. Our data suggest that the components of the species integrity do not obey the variance/invariance alternative consistently. Male terminalia and allozymes show extensive variation while sperm length distribution is strikingly similar between the geographic blocks. It is therefore inferred that sperm length might be one of the major targets of stabilizing selection. Finally, it is suggested that the striking fit between the extent of sperm heteromorphism (within male) and sperm polymorphism (between males) is instrumental in maintaining the species integrity. [ABSTRACT FROM AUTHOR]

Abstract  The control region in insects is the major noncoding region in animal mitochondrial DNA (mtDNA), and is responsible for a large part of the variation in the DNA sequence and size of the genome of this organelle. In this study, the mtDNA control region, two intergenic spacers and tRNA genes of a Zaprionus indianus strain were cloned, sequenced and compared with other Drosophila species. The overall A+T content in the Z. indianus control region is 94.3%, and a comparison with other Drosophila species demonstrated that the most conserved region appears to be the 420 base pairs nearest to the tRNAile, similar to the findings of other authors. We also describe conserved sequence blocks, including a poly-T involved in the replication process of Drosophila mtDNA; a putative secondary structure also involved in the replication process and repeated sequences. tRNAile sequence demonstrated the greatest variability when the tRNA sequences of species were compared. [ABSTRACT FROM AUTHOR]

Abstract   Drosophila simulans strains originating from Madagascar and nearby islands in the Indian Ocean often differ from those elsewhere in the number of sex comb teeth and the degree of morphological anomaly in hybrids with D. melanogaster. Here, we report a strong segregation distortion in the F1 intercross between two D. simulans strains originating from Madagascar and the US, possibly at both the gametic and zygotic levels. Strong bias against alleles of the Madagascar strain was observed for all ten marker loci distributed over the entire second chromosome in the F1 intercross, but only a few showed a weak distortion in the isogenic backgrounds of either strains. Significant deviations of genotype frequencies from Hardy–Weinberg proportions were consistently observed for the second chromosome. By contrast, the X and third chromosomes did not show any strong segregation distortion. Crossover frequency on the second chromosome was uniformly reduced in isogenic backgrounds whereas the map lengths in the F1 intercross were comparable to or larger than that of the standard D. melanogaster map. We discuss these findings in relation to previous studies on other traits and interspecific differences between D. mauritiana, which is endemic to Mauritius Island, and D. simulans. [ABSTRACT FROM AUTHOR]

Abstract  The human cancer susceptibility gene, BRCA2, functions in double-strand break repair by homologous recombination, and it appears to function via interaction of a repetitive region (“BRC repeats”) with RAD-51. A putatively simpler homolog, dmbrca2, was identified in Drosophila melanogaster recently and also affects mitotic and meiotic double-strand break repair. In this study, we examined patterns of repeat variation both within Drosophila pseudoobscura and among available Drosophila genome sequences. We identified extensive variation within and among closely related Drosophila species in BRC repeat number, to the extent that variation within this genus recapitulates the extent of variation found across the entire animal kingdom. We describe patterns of evolution across species by documenting recent repeat expansions (sometimes in tandem arrays) and homogenizations within available genome sequences. Overall, we have documented patterns and modes of evolution in a new model system of a gene which is important to human health. [ABSTRACT FROM AUTHOR]

Abstract  Gene families are composed of closely related genes and are an important part of eukaryotic genomes. In the proximal region of the X chromosome of Drosophila melanogaster there is a cluster of four tandem Sdic genes, located between the gene Cdic and the gene AnnX. Sdic is a chimeric gene that encodes a novel protein with sperm-specific expression. It had been hypothesized that the Sdic gene cluster was formed after the split of D. melanogaster and D. simulans. To study the evolution of this cluster, the sequence of this region was studied in several Drosophilidae species. In all species analyzed, Sdic genes are absent and AnnX and Cdic are adjacent to each other. The results allowed the inference of the ancestral situation and the reconstruction of the evolution of the cluster, and confirm that the Sdic cluster was indeed formed in the lineage that gave rise to D. melanogaster, being one of the youngest gene clusters known. [ABSTRACT FROM AUTHOR]

Abstract  The presence of the micropia retroelement from the Ty1-copia family of LTR retroelements was investigated in three species of the Drosophila cardini group. Southern blot analysis suggested the existence of at least four micropia copies in the genomes of D. cardinoides, D. neocardini and D. polymorpha populations. The high sequence similarity between dhMiF2 and Dm11 clones (micropia retroelements isolated from D. hydei and D. melanogaster, respectively) with micropia sequences amplified from D. cardini group genome supports the hypothesis that this retroelement plays an active role in horizontal transfer events between D. hydei and the D. cardini group. [ABSTRACT FROM AUTHOR]

Abstract  The gtwin retrotransposon was recently discovered in the Drosophila melanogaster genome and it is evolutionarily closer to gypsy endogenous retrovirus. This study has identified gtwin homologous sequences in the genome of D. simulans, D. sechellia, D. erecta and D. yakuba by performing homology searches against the public genome database of Drosophila species. The phylogenetic analyses of the gtwin env gene sequences of these species have shown some incongruities with the host species phylogeny, suggesting some horizontal transfer events for this retroelement. Moreover, we reported the existence of DNA sequences putatively encoding full-length Env proteins in the genomes of Drosophila species other than D. melanogaster. The results suggest that the gtwin element may be an infectious retrovirus able to invade the genome of new species, supporting the gtwin evolutionary picture shown in this work. [ABSTRACT FROM AUTHOR]

The phylogenetic relationships among nine entities of Drosophila belonging to the D. willistoni subgroup were investigated by establishing the homologous chromosomal segments of IIR chromosome, Muller’s element B (equivalent to chromosome 2L of D. melanogaster). The sibling species of the D. willistoni group investigated include D. willistoni, D. tropicalis tropicalis, D. tropicalis cubana, D. equinoxialis, D. insularis and four semispecies of the D. paulistorum complex. The phylogenetic relationships were based on the existence of segments in different triads of species, which could only be produced by overlapping inversions. Polytene banding similarity maps and break points of inversions between species are presented. The implications of the chromosomal data for the phylogeny of the species and comparisons with molecular data are discussed. The aim of this study is to produce phylogenetic trees depicting accurately the sequence of natural events that have occurred in the evolution of these sibling species. [ABSTRACT FROM AUTHOR]

The Drosophila buzzatii cluster is composed of seven cactophilic species and their known geographical distribution encompasses the open vegetation diagonal, which includes the morphoclimatic Domains of the Caatinga, Chaco and Cerrado, which are situated between the Amazon and the Atlantic forests. Besides these areas, these cactophilic species are also found in a narrow strip along the Atlantic coast from northeastern Brazil to the southern tip of the country. The hypothesis of vicariant events, defining the core areas of each species, is proposed to explain the historical diversification for the cluster. The intraspecific analysis for the cluster shows a population structure with gene flow restricted by distance, range expansion with secondary contact resulting in introgression and simpatry, especially in the limits of the species distribution, polytypic populations and assortative mating in inter population experiments. There is a variation related to these events that depends on the species and geographic origin of the population analyzed. These events are, hypothetically, described as the results of expansion and retraction of the population ranges, as a consequence of their association with cacti, which theoretically follow the expansion and retraction of dry areas during the paleoclimatic oscillations in South America, as that promoted by the glacial cycles of the Quaternary. The Drosophila buzzatii cluster is divided into two groups. The first one is composed of D. buzzatii, a species that has a broad geographic distribution and no significant differentiation between its populations. The second is the Drosophila serido sibling set, which encompasses the others species and is characterized by a significant potential for differentiation. [ABSTRACT FROM AUTHOR]

Abstract 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. [ABSTRACT FROM AUTHOR]

Abstract We used silver nitrate staining, CMA3 and FISH to study the chromosomal localization of both the major ribosomal genes and the nucleolar organizer regions as well as that of the minor ribosomal genes (5S rDNA) in two species of Batoidea, Taeniura lymma (Dasyatidae) and Raja montagui (Rajidae). In both species, all the metaphases examined showed the presence of multiple NOR-bearing sites, while the gene for 5S rRNA proved to be localized on two chromosome pairs. Furthermore, one of the two 5S rDNA sites in T. lymma was shown to be co-localized with the major ribosomal cluster. The presence of multiple nucleolar organizer regions in the two species might be interpreted as being the result of intraspecific polymorphisms, or as a phenomenon of the amplified transposition of mobile elements of the genome. We also determined the nucleotide sequence of the 5S rRNA gene, consisting of 564 bp in R. montagui and 612 bp in T. lymma. We also found TATA-like and (TGC)n trinucleotides, (CA)n dinucleotides and (GTGA)n tetranucleotides, which probably influence gene regulation. [ABSTRACT FROM AUTHOR]

Abstract Drosophila sechellia is an island endemic of the Seychelles. After its geographic isolation on these islands, D. sechellia evolved into a host specialist on the fruit of Morinda citrifolia a fruit often noxious and repulsive to Drosophila. Specialization on M. citrifolia required the evolution of a suite of adaptations, including resistance to and preference for some of the toxins found in this fruit. Several of these adaptive traits have been studied genetically. Here, I summarize what is known about the genetics of these traits and briefly describe the ecological and geographical context that shaped the evolution of these characters. The data from D. sechellia suggest that adaptations are not as genetically complex as historically thought, although almost all of the adaptations of D. sechellia involve several genes. [ABSTRACT FROM AUTHOR]

Understanding the significance of electrophoretic variation is of interest for both ecological and evolutionary genetics. Although there has been a very active neutralist–selectionist debate about the patterns of electrophoretic variation in natural populations, it is only recently that charged amino acids have been shown to be important in enzyme adaptation. In this study we carried out a broad electrophoretic survey of amylase variation in 150 species of Drosophilids. The distribution of amylase electromorphs was found to be correlated with the geographical origin of the flies. Generally the faster migrating variants are found in warmer temperatures. There is also a correlation with the feeding habits of the species, in particular, fungus feeders consistently showed a deviating pattern of electrophoretic mobility. These correlations between ecological diversity and electrophoretic patterns indicate that at least some of the changes in charged amino acids are adaptive, and result from selection to cope with specific environments. [ABSTRACT FROM AUTHOR]

Illegitimate recombination (IR) is a process that takes place far more often than homologous recombination and is characterized by the recombination between non-homologous or short homologous sequences. The consequences of IR frequently emerge after the introduction of DNA in cell lines because it more frequently integrates in non-homologous than in homologous regions of the host genome. As a result, unexpected truncated or elongated products may be found. By not discarding those products as transfection artifacts, but by studying how they are generated, it might elucidate a possible molecular mechanism of IR. Here we review the current literature describing different mechanisms by which non-homologous DNA recombination can be induced. [ABSTRACT FROM AUTHOR]

Sdic is a new gene that evolved recently in the lineage of Drosophila melanogaster. It was formed from a duplication and fusion of the gene AnnX, which encodes annexin X, and Cdic, which encodes the intermediate polypeptide chain of the cytoplasmic dynein. The fusion joins AnnX exon 4 with Cdic intron 3, which brings together three putative promoter elements for testes- specific expression of Sdic: the distal conserved element (DCE) and testes-specific element (TSE) are derived from AnnX, and the proximal conserved element (PCE) from Cdic intron 3. Sdic transcription initiates within the PCE, and translation is initiated within the sequence derived from Cdic intron 3, continuing through a 10 base pair insertion that creates a new splice donor site that enables the new coding sequence derived from intron 3 to be joined with the coding sequence of Cdic exon 4. A novel protein is created lacking 100 residues at the amino end that contain sequence motifs essential for the function of cytoplasmic dynein intermediate chains. Instead, the amino end is a hydrophobic region of 16 residues that resembles the amino end of axonemal dynein intermediate chains from other organisms. The downstream portion of Sdic features large deletions eliminating Cdic exons v2 and v3, as well as multiple frameshift deletions or insertions. The new protein becomes incorporated into the tail of the mature sperm and may function as an axonemal dynein intermediate chain. The new Sdic gene is present in about 10 tandem repeats between the wildtype Cdic and AnnX genes located near the base of the X chromosome. The implications of these findings are discussed relative to the origin of new gene functions and the process of speciation. [ABSTRACT FROM AUTHOR]

The aim of this work is to analyze the homogamy previously detected between two natural populations of Drosophila melanogaster from Brazzaville. It is shown that mating isolation was still maintained under laboratory conditions 10 years after the populations samples were trapped. Isolation seemed to be due mainly to pre-mating isolation and we checked for any suggestion of post-mating mortality of hybrids. Pre-mating isolation was not symmetrical, and significant χ2 values were found in 3/4 possible 3-way mating choice experiments. The only exception involved a male from the countryside and two females (one from each population) for which no significant mating preference was detected. Mortality of hybrids was intermediate between those of the parental strains showing a clear maternal effect and the existence of partial dominance. Major differences in the cuticular hydrocarbons were also found and they could account for the isolation. These findings in populations from African breweries indicate that they are closely related to European ones, suggesting that this phenomenon is not a case of sympatric speciation, but probably attributable to the reintroduction of an allopatric population. [ABSTRACT FROM AUTHOR]

As it is the case for non-coding regions, the coding regions of organisms can be expanded or shrunk during evolutionary processes. However, the dynamics of coding regions are expected to be more correlated with functional complexity and diversity than are the dynamics of non-coding regions. Hence, it is interesting to investigate the increase of diversity in coding regions – the origin and evolution of new genes – because this provides a new component to the genetic variation underlying the diversity of living organisms. Here, we examine what is known about the mechanisms responsible for the increase in gene number. Every mechanism affects genomes in a distinct way and to a different extent and it appears that certain organisms favor particular mechanisms. The detail of some interesting gene acquisitions reveals the extreme dynamism of genomes. Finally, we discuss what is known about the fate of new genes and conclude that many of the acquisitions are likely to have been driven by natural selection; they increase functional complexity, diversity, and/or adaptation of species. Despite this, the correlation between complexity of life and gene number is low and closely related species (with very similar life histories) can have very different number of genes. We call this phenomenon the G-value paradox. [ABSTRACT FROM AUTHOR]

From illustrative examples of research on the best-studied group of species to date, Drosophila melanogaster and its closest relatives, we argue that selection is multifarious, but often hidden. Selective fixation of new, highly advantageous alleles is the most parsimonious explanation for a typical pattern of molecular variation observed in genomic regions characterized by very low recombination: drastically reduced DNA sequence variation within species and typical levels of sequence divergence among species. At the same time, the identity of the gene (or genes) influenced by selection is not just difficult to discern; it may be impossible. Studies of the genetic basis of reproductive isolation demonstrate that, although the D. melanogaster complex species appear virtually identical, dozens of currently unidentified genes contribute to hybrid sterility. We argue that these findings are best explained by selectively-driven functional divergence and demonstrate the multifarious nature of selection. Although multifarious selection certainly occurs, the exact characters responsible for differences in survival and reproductive success are unknown. We do not see these inherent limits as a cause for despair or a problem for evolutionary biology. Instead, we hope to raise awareness of these complexities of evolution by highlighting both the progress and the limitations of characterizing multifarious natural selection. [ABSTRACT FROM AUTHOR]

7-tricosene (7T) and 7-pentacosene (7P) are the major components of cuticular hydrocarbons in Drosophila simulans and D. melanogaster males. A chemical study of 16 isofemale lines of D. melanogaster sampled at the first and eighth generations in laboratory conditions showed the stability of chromatographical profiles. Then a large scale study of male 7T/7P polymorphism was performed with 85 populations of D. melanogaster and 29 of D. simulans collected all over the world. There were significant correlations of the values of the balanced ratio (7T − 7P)/(7T + 7P) with geo-climatic parameters, such as latitude, longitude, mean temperature, temperature range and vapour pressure. Parallel variations were also reported for the homologous linear alkanes (23 and 25 Carbon atoms) but not for the longer branched alkanes (27 and 29 Carbon atoms). No correlation was significant for the D. simulans populations studied. In this species a similar polymorphism of 7T/7P was found but restricted to a few populations from West Equatorial Africa. [ABSTRACT FROM AUTHOR]

Transposable elements are short but complex pieces of DNA or RNA containing a streamlined minimal-genome with the capacity for its selfish replication in a foreign genomic environment. Cis-regulatory sections within the elements orchestrate tempo and mode of TE expression. Proteins encoded by TEs mainly direct their own propagation within the genome by recruitment of host-encoded factors. On the other hand, TE-encoded proteins harbor a very attractive repertoire of functional abilities for a cell. These proteins mediate excision, replication and integration of defined DNA fragments. Furthermore, some of these proteins are able to manipulate important host factors by altering their original function. Thus, if the host genome succeeds in domesticating such TE-encoded proteins by taming their ‘anarchistic behavior,’ such an event can be considered as an important evolutionary innovation for its own benefit. In fact, the domestication of TE-derived cis-regulatory modules and protein coding sections took place repeatedly in the course of genome evolution. We will present prominent cases that impressively demonstrate the beneficial impact of TEs on host biology over evolutionary time. Furthermore, we will propose that molecular domestication might be considered as a resumption of the same evolutionary process that drove the transition from ‘primitive genomes’ to ‘modern’ ones at the early dawn of life, that is, the adaptive integration of a short piece of autonomous DNA into a complex regulatory network. [ABSTRACT FROM AUTHOR]

Drosophila simulans presents a large variation in copy number among various transposable elements (TEs) and among natural populations for a given element. Some elements such as HMS beagle, blood, flea, tirant, coral, prygun jockey, F, nomade and mariner are absent in most populations, except in one or two which have copies on their chromosome arms. This suggests that some TEs are being awakened in D. simulans and are in the process of invading the species while it is colonizing the world. The elements 412 and roo/B104 present a wide insertion polymorphism among D. simulans populations, but only the 412 copy number follows a temperature cline. One population (Canberra from Australia) has a very high copy number for the 412 element and for many other TEs as well, indicating that some populations may have lost control of some of their TEs. While the 412 transposition rate is similar in all populations, its transcription level throughout developmental stages varies with populations, depending on copy number. Populations with 412 copy number higher than 10–12 exhibit co-suppression, while the expression in populations with lower numbers depends on the insertion location. All these results suggest genomic invasions by 412 and other TEs during the worldwide spread of the D. simulans species. [ABSTRACT FROM AUTHOR]

We present a global analysis of the distribution of 43 transposable elements (TEs) in 228 species of the Drosophila genus from our data and data from the literature. Data on chromosome localization come from in situ hybridization and presence/absence of the elements from southern analyses. This analysis shows great differences between TE distributions, even among closely related species. Some TEs are distributed according to the phylogeny of their host specie; others do not entirely follow the phylogeny, suggesting horizontal transfers. A higher number of insertion sites for most TEs in the genome of D. melanogaster is observed when compared with that in D. simulans. This suggests either intrinsic differences in genomic characteristics between the two species, or the influence of differing effective population sizes, although biases due to the use of TE probes coming mostly from D. melanogaster and to the way TEs are initially detected in species cannot be ruled out. Data on TEs more specific to the species under consideration are necessary for a better understanding of their distribution in organisms and populations. [ABSTRACT FROM AUTHOR]

Investigations on the chromosomal inversion polymorphism were conducted on a Korean (Taenung) natural population of D. melanogaster during the period 1978 to 1992. A total of 66 different endemic and cosmopolitan inversions were found on both major chromosome pairs II and III. Some of them proved to be rare cosmopolitan types (2LKA, 2LNS, 2LF, 2RCy, 3LM, 3RKI, and 3RK), while others were endemics. The distribution of breakpoints for endemic and rare cosmopolitan inversions are not random along the two autosome arms.With respect to frequency changes, the 15-year survey revealed that five of the cosmopolitan types (2Lt, 2RNS, 3LP, 3RC, and 3RMo) exhibit cyclical frequency changes, whereas gene arrangement 3RP shows relatively stable frequencies. Tests for correlations between gene arrangement frequencies and several climatic variables gave no clear evidence for such relationships. Only one correlation coefficient out of 64 was statistically significant. [ABSTRACT FROM AUTHOR]