Origin of scarlet gynogenetic triploid Carassius fish: Implications for conservation of the sexual–gynogenetic complex

天然記念物ヒブナの起源を解明 --クローン繁殖のはずなのにキンギョと交雑--. 京都大学プレスリリース. 2022-10-21.Conservation of sperm-dependent asexual (gynogenetic) species is challenging due to their complicated ecological dynamics, which requires the stable coexistence with their sperm-providing sexual relatives, who often share similar niches. A symbolic but vulnerable gynogenetic animal is the scarlet Carassius fish, or Hibuna, which is mainly found in Lake Harutori on Hokkaido, Japan. Although Hibuna in Lake Harutori has been protected as a symbol of the Natural Monument of Japan, it has recently suffered population decline. To establish an effective conservation strategy for Hibuna, we investigated its origin, reproductive mode, and genetic diversity, with reference to the surrounding wild populations, using nuclear microsatellites and mitochondrial gene sequences. Our genetic analyses revealed that the main ploidy of Hibuna was triploid or tetraploid, and it reproduces gynogenetically. However, no co-existing sexual diploid Carassius was detected among our samples, suggesting that the sexual diploids and the gynogenetic population including Hibuna would be at risk of co-extirpation. In addition, Hibuna showed high genetic/clonal diversity and most Hibuna had nonindigenous mitochondrial haplotypes that are mostly identical to those reported from goldfish. These results indicate that Hibuna most probably originated from hybridization between indigenous gynogenetic triploids and goldfish introduced about 100 years ago, involving rare sexual reproduction. This spontaneous long-term field experiment exemplifies the recently documented diversification process of gynogenetic Carassius via complex interploidy gene flow. Although the priority to be placed on the conservation of Hibuna is controversial, the maintenance of gynogenetic Carassius, including Hibuna, requires strategic conservation of sexual populations

Interploidy gene flow involving the sexual-asexual cycle facilitates the diversification of gynogenetic triploid Carassius fish

クローン繁殖フナは稀に有性生殖をしながら繁栄 --遺伝的に多様なクローンフナが存在する謎を解明--. 京都大学プレスリリース. 2021-11-19.Asexual vertebrates are rare and at risk of extinction due to their restricted adaptability through the loss of genetic recombination. We explore the mechanisms behind the generation and maintenance of genetic diversity in triploid asexual (gynogenetic) Carassius auratus fish, which is widespread in East Asian fresh waters and exhibits one of the most extensive distribution among asexual vertebrates despite its dependence on host sperm. Our analyses of genetic composition using dozens of genetic markers and genome-wide transcriptome sequencing uncover admixed genetic composition of Japanese asexual triploid Carassius consisting of both the diverged Japanese and Eurasian alleles, suggesting the involvement of Eurasian lineages in its origin. However, coexisting sexual diploid relatives and asexual triploids in Japan show regional genetic similarity in both mitochondrial and nuclear markers. These results are attributed to a unique unidirectional gene flow from diploids to sympatric triploids, with the involvement of occasional sexual reproduction. Additionally, the asexual triploid shows a weaker population structure than the sexual diploid, and multiple triploid lineages coexist in most Japanese rivers. The generated diversity via repeated interploidy gene flow as well as an increased establishment of immigrants is assumed to offset the cost of asexual reproduction and might contribute to the successful broad distribution of this asexual vertebrate

無性生殖をする脊椎動物の起源と多様性，進化的な意義 : 雌性発生・雑種発生をする魚類の比較研究

京都大学0048新制・課程博士博士(理学)甲第20956号理博第4408号新制||理||1633(附属図書館)京都大学大学院理学研究科生物科学専攻(主査)准教授 渡辺 勝敏, 教授 曽田 貞滋, 教授 中川 尚史学位規則第4条第1項該当Doctor of ScienceKyoto UniversityDGA