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Christian Schlotterer - One of the best experts on this subject based on the ideXlab platform.
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low levels of transposable element activity in drosophila Mauritiana causes and consequences
bioRxiv, 2015Co-Authors: Robert Kofler, Christian SchlottererAbstract:Transposable elements (TEs) are major drivers of genomic and phenotypic evolution, yet many questions about their biology remain poorly understood. Here, we compare TE abundance between populations of the two sister species D. Mauritiana und D. simulans and relate it to the more distantly related D. melanogaster. The low population frequency of most TE insertions in D. melanogaster and D. simulans has been a key feature of several models of TE evolution. In D. Mauritiana, however, the majority of TE insertions are fixed (66%). We attribute this to a lower transposition activity of up to 47 TE families in D. Mauritiana, rather than stronger purifying selection. Only three families, including the extensively studied Mariner, may have a higher activity in D. Mauritiana. This remarkable difference in TE activity between two recently diverged Drosophila species (≈ 250,000 years), also supports the hypothesis that TE copy numbers in Drosophila may not reflect a stable equilibrium where the rate of TE gains equals the rate of TE losses by negative selection. We propose that the transposition rate heterogeneity results from the contrasting ecology of the two species: the extent of vertical extinction of TE families and horizontal acquisition of active TE copies may be very different between the colonizing D. simulans and the island endemic D. Mauritiana. Our findings provide novel insights in the evolution of TEs in Drosophila and suggest that the ecology of the host species could be a major, yet underappreciated, factor governing the evolutionary dynamics of TEs.
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genome wide patterns of natural variation reveal strong selective sweeps and ongoing genomic conflict in drosophila Mauritiana
Genome Research, 2013Co-Authors: Ram Vinay Pandey, Robert Kofler, Christian SchlottererAbstract:Intragenomic conflict describes the phenomenon that within an organism some genetic elements (e.g., segregation distorters) increase their transmission at the expense of others (Werren 2011). Due to the preferential transmission, such elements spread in the population and can leave a characteristic trace of strongly reduced variability in the genome that resembles a selective sweep (Derome et al. 2004). Population genetic analyses of segregation distortion systems in Drosophila did not find a molecular signature similar to a classic selective sweep (Derome et al. 2004, 2008; Presgraves et al. 2009; Kingan et al. 2010; Bastide et al. 2011). The patterns of variability instead resembled partial selective sweeps, suggesting that the genetic element increased in frequency but did not reach fixation. This observation is consistent with the fact that elements of intragenomic conflict are frequently deleterious when homozygous (Wallace 1948; Curtsinger and Feldman 1980) or that suppressors of the intragenomic conflict have evolved (Hamilton 1967). In the Drosophila melanogaster complex, only a small number of genes involved in intragenomic conflict have been identified within natural populations (e.g., Sandler et al. 1959; Mercot et al. 1995). While this may suggest that intragenomic conflict is a relatively rare event, it needs to be considered that there is a strong ascertainment bias: The rapid spread of driver alleles is either prevented by a quick fixation of suppressor alleles, or, in case of sex chromosome–linked segregation distorters, populations with an advanced intragenomic conflict become extinct (Gershenson 1928; Hamilton 1967; Lyttle 1977). In both cases, past episodes of genomic conflict cannot be recognized in an intraspecific polymorphism analysis. Indeed, consistent with the idea that genomic conflict is a common phenomenon, detailed analysis of hybrids showed that “speciation” genes tend to be involved in intragenomic conflict, but their effect could be only detected in hybrids (Perez et al. 1993; Dermitzakis et al. 2000; Tao et al. 2001; Presgraves et al. 2003; Phadnis and Orr 2009; Tang and Presgraves 2009). Several genes involved in intragenomic conflict in Drosophila were discovered in the Drosophila simulans clade that consists of three recently diverged species, the cosmopolitan D. simulans and the island endemics Drosophila Mauritiana and Drosophila sechellia. D. Mauritiana was the first species for which a “speciation” gene could be characterized at the molecular level: In hybrid crosses with D. simulans, the Odysseus (OdsH) allele of D. Mauritiana together with additional tightly linked factors causes hybrid male sterility in the F1 generation (Perez and Wu 1995; Ting et al. 1998) and has been later identified as a gene involved in genomic conflict (Bayes and Malik 2009). Another D. Mauritiana gene, too much yin (tmy), causes both, hybrid male sterility and segregation distortion in crosses between D. Mauritiana and D. simulans (Tao et al. 2001), whereas the heterochromatic hlx locus causes hybrid lethality between D. Mauritiana and both of its sister species (Cattani and Presgraves 2009). Additional elements of intragenomic conflict have been identified between the more distantly related D. melanogaster and D. simulans, in which the interaction between the genes Hmr and Lhr contributes to hybrid male lethality in crosses between D. melanogaster and D. simulans (Brideau et al. 2006; Maheshwari and Barbash 2012). The D. simulans alleles of two nucleoporin genes, Nup962 and Nup160, cause recessive male lethality when crossed to a D. melanogaster X chromosome (Presgraves et al. 2003; Tang and Presgraves 2009), a phenomenon that has been also linked to genomic conflict (Presgraves 2007; Presgraves and Stephan 2007). While the NUP96 protein is highly conserved between D. simulans and D. Mauritiana, the D. Mauritiana allele of Nup96 has no hybrid-lethal effect, which suggests more complex genetic interactions leading to Nup96-dependent incompatibility (Barbash 2007). Despite the importance of D. Mauritiana as a model for understanding the genetic basis of speciation, an annotated genome sequence is not yet available. Using de novo assembly, we generated a draft genome of D. Mauritiana and estimated genome-wide polymorphism patterns from Pool-seq data. Our data show the impact of genes involved in genomic conflict on the evolution of the D. Mauritiana lineage. Nucleoporin genes, implicated in hybrid incompatibilities that have evolved between D. simulans and D. melanogaster, are possible targets of recurrent positive selection due to ongoing genomic conflict (Presgraves and Stephan 2007). Unlike previous genome-wide polymorphism surveys of D. simulans and D. melanogaster (Begun et al. 2007; Langley et al. 2012), we find that in the D. Mauritiana lineage, nucleoporins are among the genes showing the strongest evidence of recurrent adaptive evolution. Furthermore, the presence of a pair of meiotic drive genes and a “speciation” gene at the center of two valleys of strongly reduced variability suggests that these sweeps have been caused by genes involved in genomic conflict.
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genome wide patterns of natural variation reveal strong selective sweeps and ongoing genomic conflict in drosophila Mauritiana
Genome Research, 2013Co-Authors: Ram Vinay Pandey, Robert Kofler, Christian SchlottererAbstract:Although it is well understood that selection shapes the polymorphism pattern in Drosophila, signatures of classic selective sweeps are scarce. Here, we focus on Drosophila Mauritiana, an island endemic, which is closely related to Drosophila melanogaster. Based on a new, annotated genome sequence, we characterized the genome-wide polymorphism by sequencing pooled individuals (Pool-seq). We show that the interplay between selection and recombination results in a genome-wide polymorphism pattern characteristic for D. Mauritiana. Two large genomic regions (>500 kb) showed the signature of almost complete selective sweeps. We propose that the absence of population structure and limited geographic distribution could explain why such pronounced sweep patterns are restricted to D. Mauritiana. Further evidence for strong adaptive evolution was detected for several nucleoporin genes, some of which were not previously identified as genes involved in genomic conflict. Since this adaptive evolution is continuing after the split of D. Mauritiana and Drosophila simulans, we conclude that genomic conflict is not restricted to short episodes, but rather an ongoing process in Drosophila.
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multiple hybridization events between drosophila simulans and drosophila Mauritiana are supported by mtdna introgression
Molecular Ecology, 2010Co-Authors: Maria D S Nunes, Pablo Orozcoter Wengel, Michaela Kreissl, Christian SchlottererAbstract:The study of speciation has advanced considerably in the last decades because of the increased application of molecular tools. In particular, the quantification of gene flow between recently diverged species could be addressed. Drosophila simulans and Drosophila Mauritiana diverged, probably allopatrically, from a common ancestor approximately 250 000 years ago. However, these species share one mitochondrial DNA (mtDNA) haplotype indicative of a recent episode of introgression. To study the extent of gene flow between these species, we took advantage of a large sample of D. Mauritiana and employed a range of different markers, i.e. nuclear and mitochondrial sequences, and microsatellites. This allowed us to detect two new mtDNA haplotypes (MAU3 and MAU4). These haplotypes diverged quite recently from haplotypes of the siII group present in cosmopolitan populations of D. simulans. The mean divergence time of the most diverged haplotype (MAU4) is approximately 127 000 years, which is more than 100 000 years before the assumed speciation time. Interestingly, we also found some evidence for gene flow at the nuclear level because an excess of putatively neutral loci shows significantly reduced differentiation between D. simulans and D. Mauritiana. Our results suggest that these species are exchanging genes more frequently than previously thought.
Chungi Wu - One of the best experts on this subject based on the ideXlab platform.
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sex in drosophila Mauritiana a very high level of amino acid polymorphism in a male reproductive protein gene acp26aa
Molecular Biology and Evolution, 2001Co-Authors: Shunchern Tsaur, Chauti Ting, Chungi WuAbstract:: Many genes pertaining to male reproductive functions have been shown to evolve rapidly between species, and evidence increasingly suggest the influence of positive Darwinian selection. The accessory gland protein gene (Acp26Aa) of Drosophila is one such example. In order to understand the mechanism of selection, it is often helpful to examine the pattern of polymorphism. We report here that the level of amino acid polymorphism in the N-terminal quarter of Acp26Aa is high in Drosophila melanogaster and is unprecedented in its sibling species Drosophila Mauritiana. We postulate that (1) this N-terminal segment may play a role in sperm competition, and (2) D. Mauritiana may have been under much more intense sexual selection than other species. Both postulates have important ramifications and deserve to be tested rigorously.
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Evidence for complex genic interactions between conspecific chromosomes underlying hybrid female sterility in the Drosophila simulans clade.
Genetics, 1994Co-Authors: A. W. Davis, Erik G. Noonburg, Chungi WuAbstract:F(1) hybrid females between the sibling species Drosophila simulans, Drosophila Mauritiana and Drosophila sechellia are completely fertile. However, we have found that female sterility can be observed in F(2) backcross females who are homozygous for D. simulans X chromosomes and homozygous for autosomal regions from either D. Mauritiana or D. sechellia. Our results indicate that neither D. Mauritiana autosome (2 or 3) can cause complete female sterility in a D. simulans background. The simultaneous presence of homozygous regions from both the second and third chromosomes of D. Mauritiana, however, causes nearly complete female sterility which cannot be accounted for by their individual effects. The two autosomes of D. sechellia may show a similar pattern. From the same crosses, we also obtained evidence against a role for cytoplasmic or maternal effects in causing hybrid male sterility between these species. Taken with the results presented elsewhere, these observations suggest that epistatic interactions between conspecific genes in a hybrid background may be the prevalent mode of hybrid sterility between recently diverged species.
Hugh M Robertson - One of the best experts on this subject based on the ideXlab platform.
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wolbachia infections and the expression of cytoplasmic incompatibility in drosophila sechellia and d Mauritiana
Genetics, 1995Co-Authors: Rosanna Giordano, Scott Leslie Oneill, Hugh M RobertsonAbstract:Various stocks of Drosophila Mauritiana and D. sechellia were found to be infected with Wolbachia, a Rickettsia-like bacterium that is known to cause cytoplasmic incompatibility and other reproductive abnormalities in arthropods. Testing for the expression of cytoplasmic incompatibility in these two species showed partial incompatibility in D. sechellia but no expression of incompatibility in D. Mauritiana. To determine whether absence of cytoplasmic incompatibility in D. Mauritiana was due to either the bacterial or host genome, we transferred bacteria from D. Mauritiana into an uninfected strain of D. simulans, a host species known to express high levels of incompatibility with endogenous Wolbachia. We also performed the reciprocal transfer of the natural D. simulans Riverside infection into a tetracycline-treated stock of D. Mauritiana. In each case, the ability to express incompatibility was unaltered by the different host genetic background. These experiments indicate that in D. simulans and D. Mauritiana expression of the cytoplasmic incompatibility phenotype is determined by the bacterial strain and that D. Mauritiana harbors a neutral strain of Wolbachia.
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the mariner transposable element is widespread in insects
Nature, 1993Co-Authors: Hugh M RobertsonAbstract:THE mariner transposable element is a small member of the short inverted terminal repeat class thought to transpose through a DNA intermediate1. Originally described in Drosophila Mauritiana2, it is now known in several species of the family Drosophilidae3,4, and in a moth Hyalophora cecropia5. Here I use primers designed to represent regions of amino-acid conservation between the putative transposase genes of the D. Mauritiana and H. cecropia elements to amplify equivalent regions of presumed mariner elements from ten other insects representing six additional orders, including the malaria-vector mosquito, Anopheles gambiae. Sequences of multiple clones from each species reveal a diverse array of mariner elements, with multiple subfamilies in the genomes of some insects, indicating both vertical inheritance and horizontal transfers. An intact open reading frame in at least one clone from each species suggests each may carry functional transposable elements. Therefore the mariner element is an excellent candidate for development of genetic transformation systems for non-drosophilid insects, and possibly other arthropods.
A. W. Davis - One of the best experts on this subject based on the ideXlab platform.
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Evidence for complex genic interactions between conspecific chromosomes underlying hybrid female sterility in the Drosophila simulans clade.
Genetics, 1994Co-Authors: A. W. Davis, Erik G. Noonburg, Chungi WuAbstract:F(1) hybrid females between the sibling species Drosophila simulans, Drosophila Mauritiana and Drosophila sechellia are completely fertile. However, we have found that female sterility can be observed in F(2) backcross females who are homozygous for D. simulans X chromosomes and homozygous for autosomal regions from either D. Mauritiana or D. sechellia. Our results indicate that neither D. Mauritiana autosome (2 or 3) can cause complete female sterility in a D. simulans background. The simultaneous presence of homozygous regions from both the second and third chromosomes of D. Mauritiana, however, causes nearly complete female sterility which cannot be accounted for by their individual effects. The two autosomes of D. sechellia may show a similar pattern. From the same crosses, we also obtained evidence against a role for cytoplasmic or maternal effects in causing hybrid male sterility between these species. Taken with the results presented elsewhere, these observations suggest that epistatic interactions between conspecific genes in a hybrid background may be the prevalent mode of hybrid sterility between recently diverged species.
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genetics of reproductive isolation in the drosophila simulans clade complex epistasis underlying hybrid male sterility
Genetics, 1994Co-Authors: E L Cabot, A. W. Davis, Norman A JohnsonAbstract:We have analyzed the sterility associated with introgressions of the distal one-fourth of the X chromosome from either Drosophila Mauritiana or Drosophila sechellia into the genome of Drosophila simulans using a series of visible and DNA markers. Because in Drosophila hybrids, male sterility is usually complete and is often tightly linked with each of several markers used in crosses, a simple genetic basis has generally been assumed. In our low resolution mapping experiment, we were not able to reject the null hypothesis that a single gene, introgressed from either D. Mauritiana or D. sechellia, is the cause of male sterility. High resolution mapping, however, reveals a much more complex picture. At least three distinct factors from D. Mauritiana, or two from D. sechellia, were identified that need to be jointly present to confer full sterility. Each individual factor by itself is relatively ineffective in causing sterility, or even a partial spermatogenic defect. Moreover, there appear to be more sterility factors on comparable introgressions from D. Mauritiana than from D. sechellia. On the basis of these observations, we propose a model which suggests that multilocus weak allele interactions are a very common cause of reproductive incompatibility between closely related species. We also present theoretical argument and empirical evidence against extrapolating the results of within-species analysis to interpret the genetic basis of species differences. The implications of this model on the theories of evolution of species differences and the attempt to understand the mechanisms of hybrid sterility/inviability at the molecular level are discussed.
Cathy C Laurie - One of the best experts on this subject based on the ideXlab platform.
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a genome wide survey of hybrid incompatibility factors by the introgression of marked segments of drosophila Mauritiana chromosomes into drosophila simulans
Genetics, 1996Co-Authors: John R True, B S Weir, Cathy C LaurieAbstract:In hybrids between Drosophila simulans and D. Mauritiana, males are sterile and females are fertile, in compliance with HALDANE`s rule. The genetic basis of this phenomenon was investigated by introgression of segments of the Mauritiana genome into a simulans background. A total of 87 positions throughout the Mauritiana genome were marked with P-element insertions and replicate introgressions were made by repeated backcrossing to simulans for 15 generations. The fraction of hemizygous X chromosomal introgressions that are male sterile is {approximately}50% greater than the fraction of homozygous autosomal segments. This result suggests that male sterility factors have evolved at a higher rate on the X, but chromosomal differences in segment length cannot be ruled out. The fraction of homozygous autosomal introgressions that are male sterile is several times greater than the fraction that are either female sterile or inviable. This observation strongly indicates that male sterility factors have evolved more rapidly than either female sterility or inviability factors. These results, combined with previous work on these and other species, suggest that HALDANE`s rule has at least two causes: recessivity of incompatibility factors and differential accumulation of sterility factors affecting males and females. 50 refs., 4 figs., 3 tabs.
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a genome wide survey of hybrid incompatibility factors by the introgression of marked segments of drosophila Mauritiana chromosomes into drosophila simulans
Genetics, 1996Co-Authors: John R True, B S Weir, Cathy C LaurieAbstract:In hybrids between Drosophila simulans and D. Mauritiana, males are sterile and females are fertile, in compliance with HALDANE's rule. The genetic basis of this phenomenon was investigated by introgression of segments of the Mauritiana genome into a simulans background. A total of 87 positions throughout the Mauritiana genome were marked with P-element insertions and replicate introgressions were made by repeated backcrossing to simulans for 15 generations. The fraction of hemizgyous X chromosomal introgressions that are male sterile is approximately 50% greater than the fraction of homozygous autosomal segments. This result suggests that male sterility factors have evolved at a higher rate on the X, but chromosomal differences in segment length cannot be ruled out. The fraction of homozygous autosomal introgression that are male sterile is several times greater than the fraction that are either female sterile or inviable. This observation strongly indicates that male sterility factors have evolved more rapidly than either female sterility or inviability factors. These results, combined with previous work on these and other species, suggest that HALDANE's rule has at least two causes: recessivity of incompatibility factors and differential accumulation of sterility factors affecting males and females.