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Polyploid speciation did not confer instant reproductive isolation in Capsella (Brassicaceae)

Slotte, Tanja; Huang, Huirun; Lascoux, Martin and Ceplitis, Alf LU (2008) In Molecular Biology and Evolution 25(7). p.1472-1481
Abstract
Polyploid formation is a major mode of sympatric speciation in flowering plants. Unlike other speciation processes, polyploidization is often assumed to confer instant reproductive isolation. Shared polymorphism across ploidy levels has therefore often been attributed to multiple polyploid origins, whereas the alternative hypothesis of introgressive hybridization has rarely been rigorously tested. Here, we sequence 12 nuclear loci representing 6 genes duplicated by polyploidy in 92 accessions of the tetraploid Capsella bursa-pastoris together with the corresponding loci in 21 accessions of its close diploid relative Capsella rubella. In C. bursa-pastoris accessions from western Eurasia, where the 2 species occur in partial sympatry, we... (More)
Polyploid formation is a major mode of sympatric speciation in flowering plants. Unlike other speciation processes, polyploidization is often assumed to confer instant reproductive isolation. Shared polymorphism across ploidy levels has therefore often been attributed to multiple polyploid origins, whereas the alternative hypothesis of introgressive hybridization has rarely been rigorously tested. Here, we sequence 12 nuclear loci representing 6 genes duplicated by polyploidy in 92 accessions of the tetraploid Capsella bursa-pastoris together with the corresponding loci in 21 accessions of its close diploid relative Capsella rubella. In C. bursa-pastoris accessions from western Eurasia, where the 2 species occur in partial sympatry, we find higher levels of nucleotide diversity than in accessions from eastern Eurasia, where C. rubella does not grow. Furthermore, haplotypes are shared across ploidy levels at 4 loci in western but not in eastern Eurasia. We test whether haplotype sharing is due to retention of ancestral polymorphism or due to hybridization and introgression using a coalescent-based isolation-with-migration model. In western but not in eastern Eurasia, there is evidence for unidirectional gene flow from C. rubella to C. bursa-pastoris. An independent estimate of the timing of dispersal of C. bursa-pastoris to eastern Eurasia indicates that it probably predated introgression. Our results show that polyploid speciation need not result in immediate and complete reproductive isolation, that postpolyploidization hybridization and introgression can contribute significantly to genetic variation in a newly formed polyploid, and that divergence population genetic analysis constitutes a powerful way of testing hypotheses on polyploid speciation. (Less)
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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
speciation, isolation-migration model, polyploidy, Capsella, introgression
in
Molecular Biology and Evolution
volume
25
issue
7
pages
1472 - 1481
publisher
Oxford University Press
external identifiers
  • wos:000256979100022
  • scopus:45849137397
ISSN
0737-4038
DOI
10.1093/molbev/msn092
language
English
LU publication?
yes
id
a7d39a0d-f3de-4729-a033-8adca22bb62a (old id 1190591)
date added to LUP
2008-09-08 10:31:27
date last changed
2017-11-05 03:27:55
@article{a7d39a0d-f3de-4729-a033-8adca22bb62a,
  abstract     = {Polyploid formation is a major mode of sympatric speciation in flowering plants. Unlike other speciation processes, polyploidization is often assumed to confer instant reproductive isolation. Shared polymorphism across ploidy levels has therefore often been attributed to multiple polyploid origins, whereas the alternative hypothesis of introgressive hybridization has rarely been rigorously tested. Here, we sequence 12 nuclear loci representing 6 genes duplicated by polyploidy in 92 accessions of the tetraploid Capsella bursa-pastoris together with the corresponding loci in 21 accessions of its close diploid relative Capsella rubella. In C. bursa-pastoris accessions from western Eurasia, where the 2 species occur in partial sympatry, we find higher levels of nucleotide diversity than in accessions from eastern Eurasia, where C. rubella does not grow. Furthermore, haplotypes are shared across ploidy levels at 4 loci in western but not in eastern Eurasia. We test whether haplotype sharing is due to retention of ancestral polymorphism or due to hybridization and introgression using a coalescent-based isolation-with-migration model. In western but not in eastern Eurasia, there is evidence for unidirectional gene flow from C. rubella to C. bursa-pastoris. An independent estimate of the timing of dispersal of C. bursa-pastoris to eastern Eurasia indicates that it probably predated introgression. Our results show that polyploid speciation need not result in immediate and complete reproductive isolation, that postpolyploidization hybridization and introgression can contribute significantly to genetic variation in a newly formed polyploid, and that divergence population genetic analysis constitutes a powerful way of testing hypotheses on polyploid speciation.},
  author       = {Slotte, Tanja and Huang, Huirun and Lascoux, Martin and Ceplitis, Alf},
  issn         = {0737-4038},
  keyword      = {speciation,isolation-migration model,polyploidy,Capsella,introgression},
  language     = {eng},
  number       = {7},
  pages        = {1472--1481},
  publisher    = {Oxford University Press},
  series       = {Molecular Biology and Evolution},
  title        = {Polyploid speciation did not confer instant reproductive isolation in Capsella (Brassicaceae)},
  url          = {http://dx.doi.org/10.1093/molbev/msn092},
  volume       = {25},
  year         = {2008},
}