Abstract:Background: Species of the Drosophila obscura species group (e.g., D. pseudoobscura, D. subobscura) have served as favorable models in evolutionary studies since the 1930's. Despite numbers of studies conducted with varied types of data, the basal phylogeny in this group is still controversial, presumably owing to not only the hypothetical 'rapid radiation' history of this group, but also limited taxon sampling from the Old World (esp. the Oriental and Afrotropical regions). Here we reconstruct the phylogeny o… Show more
“…Figures 2 and 3 show the phylogenies of the species obtained for TL and SRL trait, respectively. The congruence of the relationship between the species was confirmed in recent papers by Huey et al (2006) and Gao et al (2007) for the obscura group, and by Reis et al (2008) for the virilis group. For each group of species having at least two values, the mean of the trait (TL and SRL, respectively) is given with the CV in parentheses.…”
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.
“…Figures 2 and 3 show the phylogenies of the species obtained for TL and SRL trait, respectively. The congruence of the relationship between the species was confirmed in recent papers by Huey et al (2006) and Gao et al (2007) for the obscura group, and by Reis et al (2008) for the virilis group. For each group of species having at least two values, the mean of the trait (TL and SRL, respectively) is given with the CV in parentheses.…”
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.
“…The species corresponding to the black subtrees were used as outgroups in the orphan detection pipeline (see ‘Materials and methods’). Divergence times for the 12 Drosophila species are taken from Table 3 in Obbard et al (2012) (estimates based on mutation rate); for D. affinis and D. miranda from Gao et al (2007); for D. lowei from Beckenbach et al (1993). DOI:
http://dx.doi.org/10.7554/eLife.01311.01110.7554/eLife.01311.012Figure 7.Chromosomal distribution of orphans of different age classes.In each age class orphans are underrepresented on the neo-X (XR) compared to old-X (XL) (Age class 4: χ 2 -test, p=6.3 × 10 −9 ; age class 3: χ 2 -test, p=4.4 × 10 −5 ; age class 2: χ 2 -test, p=0.00590; age class 1: χ 2 -test, p=0.00876; D. pseudoobscura specific: χ 2 -test, p=0.00030). DOI:
http://dx.doi.org/10.7554/eLife.01311.012…”
Orphans are genes restricted to a single phylogenetic lineage and emerge at high rates. While this predicts an accumulation of genes, the gene number has remained remarkably constant through evolution. This paradox has not yet been resolved. Because orphan genes have been mainly analyzed over long evolutionary time scales, orphan loss has remained unexplored. Here we study the patterns of orphan turnover among close relatives in the Drosophila obscura group. We show that orphans are not only emerging at a high rate, but that they are also rapidly lost. Interestingly, recently emerged orphans are more likely to be lost than older ones. Furthermore, highly expressed orphans with a strong male-bias are more likely to be retained. Since both lost and retained orphans show similar evolutionary signatures of functional conservation, we propose that orphan loss is not driven by high rates of sequence evolution, but reflects lineage-specific functional requirements.DOI:
http://dx.doi.org/10.7554/eLife.01311.001
“…The AÁD fusion occurred following the divergence between the lineage that gave rise to pseudoobscura and the lineage currently represented by D. subobscura and close relatives. Given the ancient split between these lineages (19-22 MYA according to Gao et al 2007), the gene order around the centromere of the fused and nonfused elements might have completely changed as a result of paracentric inversions fixed in both lineages.…”
The sequencing of the 12 genomes of members of the genus Drosophila was taken as an opportunity to reevaluate the genetic and physical maps for 11 of the species, in part to aid in the mapping of assembled scaffolds. Here, we present an overview of the importance of cytogenetic maps to Drosophila biology and to the concepts of chromosomal evolution. Physical and genetic markers were used to anchor the genome assembly scaffolds to the polytene chromosomal maps for each species. In addition, a computational approach was used to anchor smaller scaffolds on the basis of the analysis of syntenic blocks. We present the chromosomal map data from each of the 11 sequenced non-Drosophila melanogaster species as a series of sections. Each section reviews the history of the polytene chromosome maps for each species, presents the new polytene chromosome maps, and anchors the genomic scaffolds to the cytological maps using genetic and physical markers. The mapping data agree with Muller's idea that the majority of Drosophila genes are syntenic. Despite the conservation of genes within homologous chromosome arms across species, the karyotypes of these species have changed through the fusion of chromosomal arms followed by subsequent rearrangement events. O NE of the primary strengths of the genus Drosophila as a model system has been the relative ease of generating detailed cytogenetic maps. Indeed, the first definitive mapping of genes to chromosomes Genetics 179: 1601-1655 ( July 2008) was performed in Drosophila melanogaster (Bridges 1916). The subsequent discovery of polytene chromosomes in the salivary glands in this same species (Painter 1934) and their codification into fine-structure genetic/ cytogenetic maps represents perhaps one of the first forays into ''genomics.'' Polytene maps (Bridges 1935;Lefevre 1976) provided an important genetic tool for mapping genes, for detecting genetic diversity within populations, and for inferring phylogenies among related species (Dobzhansky and Sturtevant 1938;Judd et al. 1972;Ashburner and Lemeunier 1976;Lemeunier and Ashburner 1976). Sturtevant and Tan (1937) laid the groundwork for comparative genomics when they established that genes within the chromosomal arms are conserved or syntenic among species. In an insightful melding of the gene mapping and evolutionary studies, H. J. Muller (1940) proposed that the genomes of Drosophila species were subdivided into a set of homologous elements represented by chromosome arms. What Muller (1940) noted, which was subsequently elaborated on by Sturtevant and Novitski (1941), was that the presumed homologs of identified mutant alleles within a chromosome arm of D. melanogaster were also confined to a single arm in other species within the genus where mapping data were available. Using D. melanogaster as a reference, Muller proposed that each of the five major chromosome arms plus the dot chromosome be given a letter designation (A-F) and that this nomenclature be used to identify equivalent linkage groups within the genus.The an...
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