Supplementary Material for: Genomic Constitution and Atypical Reproduction in Polyploid and Unisexual Lineages of the Misgurnus Loach, a Teleost Fish

The loach (Misgurnus anguillicaudatus) is an excellent animal model to elucidate biological origin and evolutionary significance of genome duplication and unisexual reproduction because artificially induced and naturally occurring polyploids and parthenogenetic (gynogenetic, androgenetic) animals can be compared. First, we summarize the chromosome manipulation techniques to induce triploids and tetraploids by inhibiting meiotic or mitotic divisions of inseminated eggs, respectively, as well as parthenogenetic animals, obtained after fertilization with genetically inactivated gametes. Then, we review the knowledge on natural polyploid and unisexual lineages found in Misgurnus loaches. A natural diploid-tetraploid complex occurs in wild populations in central China, and these diploid and tetraploid loaches reproduce bisexually. Chinese tetraploids are considered autotetraploid, which may have arisen by doubling of the entire genome of an ancestral diploid, based on cytogenetic results from FISH (fluorescence in situ hybridization) karyotypes and meiotic configurations. In contrast, gynogenetically reproducing clonal diploid lineages have been discovered in a few wild populations in Japan, although most wild-type individuals are bisexually reproducing diploids. Such clonal diploid loaches sometimes produce triploid progeny by accidental incorporation of a sperm nucleus into an unreduced diploid egg, and the resulting triploid generates haploid eggs by meiotic hybridogenesis. Unreduced diploid gametes of clonal loaches are generated by a cytological mechanism, premeiotic endomitosis, which likely occurs in the early (gonium stage) germ cells. Initiation of gynogenetic development is related to a failure of decondensation of the male (sperm) pronucleus in unreduced diploid eggs of a clonal loach. Clonal lineages may have arisen from a past hybrid event between genetically divergent groups, but their exact origins are unknown at present. See also the sister article focusing on plants by Hegarty et al. in this themed issue.泥鳅（Misgurnus anguillicaudatus）是阐释基因组加倍与单性生殖的生物学起源及进化意义的优质动物模型，这是因为可对人工诱导与自然存在的多倍体、孤雌生殖（雌核发育、雄核发育）个体开展对比研究。首先，本文综述了染色体操作技术：分别通过抑制授精卵的减数分裂与有丝分裂来诱导三倍体与四倍体，以及利用遗传失活的配子受精后获得孤雌生殖个体的相关方法。随后，本文梳理了泥鳅属（Misgurnus）自然多倍体与单性生殖谱系的相关研究进展。在中国中部的野生种群中存在天然二倍体-四倍体复合体，该类群的二倍体与四倍体泥鳅均进行有性生殖。基于荧光原位杂交（fluorescence in situ hybridization，FISH）核型与减数分裂构型的细胞遗传学研究结果，中国四倍体泥鳅被认为是同源四倍体，其可能起源于祖先二倍体的全基因组加倍。与之相对，尽管日本多数野生个体为有性生殖二倍体，但在日本少数野生种群中已发现行雌核发育的克隆二倍体谱系。此类克隆二倍体泥鳅有时会因精子核意外掺入非减数二倍体卵中而产生三倍体后代，由此产生的三倍体可通过减数分裂杂种发生（meiotic hybridogenesis）形成单倍体卵子。克隆泥鳅的非减数二倍体配子由一种细胞学机制产生：减数分裂前核内复制（premeiotic endomitosis），该过程大概率发生于早期（原生殖细胞阶段）的生殖细胞中。雌核发育的启动与克隆泥鳅非减数二倍体卵中雄性（精子）原核无法解凝密切相关。克隆谱系可能起源于遗传分化类群间的古代杂交事件，但目前其确切起源仍不明晰。另可参阅本期专题中Hegarty等人针对植物的姊妹篇综述。