Chromosomal Inversion Polymorphisms in Two Sympatric Ascidian Lineages

Yutaka Satou, Atsuko Sato, Hitoyoshi Yasuo, Yukie Mihirogi, John Bishop, Manabu Fujie, Mayumi Kawamitsu, Kanako Hisata, Noriyuki Satoh

Research output: Contribution to journalArticlepeer-review

5 Citations (Scopus)


Chromosomal rearrangements can reduce fitness of heterozygotes and can thereby prevent gene flow. Therefore, such rearrangements can play a role in local adaptation and speciation. In particular, inversions are considered to be a major potential cause for chromosomal speciation. There are two closely related, partially sympatric lineages of ascidians in the genus Ciona, which we call type-A and type-B animals in the present study. Although these invertebrate chordates are largely isolated reproductively, hybrids can be found in wild populations, suggesting incomplete prezygotic barriers. Although the genome of type-A animals has been decoded and widely used, the genome for type-B animals has not been decoded at the chromosomal level. In the present study, we sequenced the genomes of two type-B individuals from different sides of the English Channel (in the zone of sympatry with type-A individuals) and compared them at the chromosomal level with the type-A genome. Although the overall structures were well conserved between type A and type B, chromosomal alignments revealed many inversions differentiating these two types of Ciona; it is probable that the frequent inversions have contributed to separation between these two lineages. In addition, comparisons of the genomes between the two type-B individuals revealed that type B had high rates of inversion polymorphisms and nucleotide polymorphisms, and thus type B might be in the process of differentiation into multiple new types or species. Our results suggest an important role of inversions in chromosomal speciation of these broadcasting spawners.

Original languageEnglish
Article numberevab068
JournalGenome Biology and Evolution
Issue number6
Publication statusPublished - 2021 Jun 1


  • Ciona
  • chromosomal speciation
  • genomes


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