Dataset Information

Multiple hybridization events between Drosophila simulans and Drosophila mauritiana are supported by mtDNA introgression.

ABSTRACT: 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.

SUBMITTER: Nunes MD

PROVIDER: S-EPMC3035818 | biostudies-literature | 2010 Nov

REPOSITORIES: biostudies-literature

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Multiple hybridization events between Drosophila simulans and Drosophila mauritiana are supported by mtDNA introgression.

Nunes Maria D S MD Wengel Pablo Orozco-Ter PO Kreissl Michaela M Schlötterer Christian C

Molecular ecology 20101007 21

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 exte ...[more]

PMID: 20958812

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Project description:We generated RNA-seq data of Drosophila simulans and Drosophila mauritiana developing male genitalia in order to identify expression level differences between these species. These species are closely related, yet have dramatic differences in their male genital morphologies. Three independent RNA-seq library replicates were generated for Dsim w501 and Dmau D1 developing male genitalia. Flies were reared under the above conditions, and white pre-pupae collected. Males were selected using gonad size and allowed to develop in a humid container at 25ºC until stages 2 and 4.5 (see staging guide in (Hagen et al., 2019); tartan underlies the evolution of Drosophila male genital morphology). Between these stages, the claspers develop from a ridge structure to a distinct appendage separate from the surrounding tissue, and the posterior lobe has begun to extend outwards from the lateral plate primordia (Hagen et al., 2019). The heads of pupae were impaled with a needle onto a charcoal agar plate and submerged in 1xPBS. Dissection scissors were used to remove the distal tip of the pupal case and the outer membrane, and pressure applied to the abdomen to allow the developing genitalia to be quickly expelled from the pupal case and dissected away from the abdomen. Note that the entire genital arch, including internal genital organs (but not including abdominal tissue), was isolated for RNA extraction. The genitalia from fifteen males from each stage were collected and placed directly into TRIzol. RNA was then extracted using standard procedures. Quality and quantity of RNA was verified using a Qubit, and samples were sent to the Centre for Genomic Research at the University of Liverpool where dual-indexed, strand-specific RNA-seq libraries were prepared using NEBNext polyA selection and Ultra Directional RNA preparation kits. Samples were then sequenced using Illumina HiSeq 4000 (paired-end, 2x150 bp sequencing). Dsim w501 and Dmau D1 reads were mapped against reannotated reference coding sequences (Torres-Oliva et al., 2016).

Project description:BACKGROUND:The classical perspective that interspecific hybridization in animals is rare has been changing due to a growing list of empirical examples showing the occurrence of gene flow between closely related species. Using sequence data from cyt b mitochondrial gene and three intron nuclear genes (RPL9, c-myc, and RPL3) we investigated patterns of nucleotide polymorphism and divergence between two closely related toad species R. marina and R. schneideri. By comparing levels of differentiation at nuclear and mtDNA levels we were able to describe patterns of introgression and infer the history of hybridization between these species. RESULTS:All nuclear loci are essentially concordant in revealing two well differentiated groups of haplotypes, corresponding to the morphologically-defined species R. marina and R. schneideri. Mitochondrial DNA analysis also revealed two well-differentiated groups of haplotypes but, in stark contrast with the nuclear genealogies, all R. schneideri sequences are clustered with sequences of R. marina from the right Amazon bank (RAB), while R. marina sequences from the left Amazon bank (LAB) are monophyletic. An Isolation-with-Migration (IM) analysis using nuclear data showed that R. marina and R. schneideri diverged at ? 1.69 Myr (early Pleistocene), while R. marina populations from LAB and RAB diverged at ? 0.33 Myr (middle Pleistocene). This time of divergence is not consistent with the split between LAB and RAB populations obtained with mtDNA data (? 1.59 Myr), which is notably similar to the estimate obtained with nuclear genes between R. marina and R. schneideri. Coalescent simulations of mtDNA phylogeny under the speciation history inferred from nuclear genes rejected the hypothesis of incomplete lineage sorting to explain the conflicting signal between mtDNA and nuclear-based phylogenies. CONCLUSIONS:The cytonuclear discordance seems to reflect the occurrence of interspecific hybridization between these two closely related toad species. Overall, our results suggest a phenomenon of extensive mtDNA unidirectional introgression from the previously occurring R. schneideri into the invading R. marina. We hypothesize that climatic-induced range shifts during the Pleistocene/Holocene may have played an important role in the observed patterns of introgression.

Dataset Information

Multiple hybridization events between Drosophila simulans and Drosophila mauritiana are supported by mtDNA introgression.

Publications

Multiple hybridization events between Drosophila simulans and Drosophila mauritiana are supported by mtDNA introgression.

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