Comparative genome anatomy reveals evolutionary insights into a unique amphitriploid fish.
Yang WangXi-Yin LiWen-Jie XuKun WangBin WuMeng XuYan ChenLi-Jun MiaoZhong-Wei WangZhi LiXiao-Juan ZhangZhan YinBo-Tong ZhouYu-Lan YangCheng-Long ZhuMing-Liang HuJiang-Ming ZhengChen-Guang FengQiang QiuLe-Tian TianMeng LuFang PengWei-Jia LuJin-Feng TongJin-Gou TongBei-De FuPeng YuMiao DingRui-Hai GanQin-Qin ZhangJian-Bo JianChi ZhangWei-Ming HeWei YangZi-Cheng ZhaoQian-Qian ZhangQiang GaoJun-Yang XuMing-Zhou BaiYa-Ping ZhangHuan-Ming YangXiao-Dong FangWen WangLi ZhouJian-Fang GuiPublished in: Nature ecology & evolution (2022)
Triploids are rare in nature because of difficulties in meiotic and gametogenic processes, especially in vertebrates. The Carassius complex of cyprinid teleosts contains sexual tetraploid crucian carp/goldfish (C. auratus) and unisexual hexaploid gibel carp/Prussian carp (C. gibelio) lineages, providing a valuable model for studying the evolution and maintenance mechanism of unisexual polyploids in vertebrates. Here we sequence the genomes of the two species and assemble their haplotypes, which contain two subgenomes (A and B), to the chromosome level. Sequencing coverage analysis reveals that C. gibelio is an amphitriploid (AAABBB) with two triploid sets of chromosomes; each set is derived from a different ancestor. Resequencing data from different strains of C. gibelio show that unisexual reproduction has been maintained for over 0.82 million years. Comparative genomics show intensive expansion and alterations of meiotic cell cycle-related genes and an oocyte-specific histone variant. Cytological assays indicate that C. gibelio produces unreduced oocytes by an alternative ameiotic pathway; however, sporadic homologous recombination and a high rate of gene conversion also exist in C. gibelio. These genomic changes might have facilitated purging deleterious mutations and maintaining genome stability in this unisexual amphitriploid fish. Overall, the current results provide novel insights into the evolutionary mechanisms of the reproductive success in unisexual polyploid vertebrates.