2026-11-12 近畿大学
＜関連情報＞
日本産四倍体ヤマトシマドジョウにおける染色体レースの進化動態（Evolutionary dynamics of chromosomal races in the Japanese allotetraploid spined loach, Cobitis sp. ‘yamato’ species complex）
Hayato Oka, Yuki Yashima, Takeru Uechi, Takafumi Fujimoto, Tadao Kitagawa
PLOS ONE, 21(11), e0351665 2026-11-11
DOI：10.1371/journal.pone.0351665
Fig 1. Sampling locations of the Yamato spined loach (Cobitis sp. ‘yamato’ species complex) with location codes and distribution patterns of each of the chromosomal races of Yamato spined loach in Japan.
The cross filled area is the known distribution patterns of chromosomal races of them. The numbers correspond to those in S1 Table. Administrative boundaries are based on the ‘National Land Numerical Information (Administrative Areas)’ (Ministry of Land, Infrastructure, Transport and Tourism of Japan; https://nlftp.mlit.go.jp/ksj/gml/datalist/KsjTmplt-N03-2026.html), used under a CC BY 4.0 license. River data are derived from OpenStreetMap contributors (https://www.openstreetmap.org/copyright), available under the Open Database License (ODbL).
ヤマトシマドジョウ（Cobitis sp. ‘yamato’ species complex）は、異なる二倍体種の交雑によって成立した異質四倍体魚類であり、ゲノム重複後に染色体数が減少する二倍体化（レディプロイド化）の進行を観察できる貴重な脊椎動物モデルである。本研究では、日本各地の45集団を対象に染色体解析、ミトコンドリアDNA系統解析、フローサイトメトリーを実施し、染色体数の地理的分布と進化的関係を調べた。その結果、従来知られていた82～98本に加え、80本と92本の新たな染色体型を発見し、合計7種類（80、82、86、90、92、94、98本）を確認した。特に80本型は、祖先型と推定される98本型から18本減少していた。ミトコンドリアDNA解析では、染色体数の少ない集団が系統樹上の派生的な位置に分布し、染色体数が段階的に減少してきたことが示唆された。また、同じ染色体数を持つ地理的に離れた集団でも異なる系統的位置を示し、染色体再編成が独立に複数回生じたことが示された。一方、染色体数とDNA含量には正の相関が認められず、染色体の融合や再配置が減少の主因である可能性が示唆された。本研究は、脊椎動物におけるゲノム重複後の二倍体化と染色体進化の過程を理解する重要な知見を提供する。
The Japanese allotetraploid spined loach (Cobitis sp. ‘yamato’ species complex) originated through hybridization between two diploid species and provides a valuable vertebrate model for investigating rediploidization following whole-genome duplication. In this study, researchers examined the geographic distribution and evolutionary relationships of chromosomal races using chromosome analysis, mitochondrial DNA phylogenetics, and flow cytometry across populations in Japan. Seven chromosome numbers were identified: 80, 82, 86, 90, 92, 94, and 98, including two previously unreported karyotypes with 80 and 92 chromosomes. Notably, the 80-chromosome race had 18 fewer chromosomes than the putative ancestral 98-chromosome race. Mitochondrial phylogenetic analyses showed that populations with fewer chromosomes generally occupied derived positions, suggesting gradual chromosome-number reduction during evolution. Furthermore, geographically separated populations sharing the same chromosome number exhibited distinct phylogenetic relationships, indicating that chromosomal rearrangements occurred independently in multiple lineages. Flow cytometry revealed no positive correlation between chromosome number and relative DNA content, suggesting that chromosome fusion and other karyotypic rearrangements, rather than substantial DNA loss, contributed to chromosome-number reduction. These findings provide important insights into post-polyploid genome evolution, rediploidization, and chromosomal diversification in vertebrates.
