Journal
MOLECULAR BIOLOGY AND EVOLUTION
Volume 34, Issue 4, Pages 957-968Publisher
OXFORD UNIV PRESS
DOI: 10.1093/molbev/msw299
Keywords
polyploidy; Arabidopsis suecica; Arabidopsis thaliana; Arabidopsis arenosa; shared polymorphism; speciation; hybridization
Funding
- German Research Foundation DFG [SPP 1529]
- European Research Council (ERC) under the European Union [648321]
- Japan Society for the Promotion of Science
- Grants-in-Aid for Scientific Research [17K15165, 15K18583] Funding Source: KAKEN
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Polyploidy is an example of instantaneous speciation when it involves the formation of a new cytotype that is incompatible with the parental species. Because new polyploid individuals are likely to be rare, establishment of a new species is unlikely unless polyploids are able to reproduce through self-fertilization (selfing), or asexually. Conversely, selfing (or asexuality) makes it possible for polyploid species to originate from a single individual-a bona fide speciation event. The extent to which this happens is not known. Here, we consider the origin of Arabidopsis suecica, a selfing allopolyploid between Arabidopsis thaliana and Arabidopsis arenosa, which has hitherto been considered to be an example of a unique origin. Based on whole-genome re-sequencing of 15 natural A. suecica accessions, we identify ubiquitous shared polymorphism with the parental species, and hence conclusively reject a unique origin in favor of multiple founding individuals. We further estimate that the species originated after the last glacial maximum in Eastern Europe or central Eurasia (rather than Sweden, as the name might suggest). Finally, annotation of the self-incompatibility loci in A. suecica revealed that both loci carry non-functional alleles. The locus inherited from the selfing A. thaliana is fixed for an ancestral non-functional allele, whereas the locus inherited from the outcrossing A. arenosa is fixed for a novel loss-offunction allele. Furthermore, the allele inherited from A. thaliana is predicted to transcriptionally silence the allele inherited from A. arenosa, suggesting that loss of self-incompatibility may have been instantaneous.
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