Meiosis and gametogenesis in hybrid, polyploid, and clonal fishes: case studies in the dojo loach Misgurnus anguillicaudatus

Abstract

Hybrid, polyploid, and clonal fishes are found naturally in wild populations, but they can also be induced artificially by cross-breeding and chromosome manipulation. The dojo loach Misgurnus anguillicaudatus includes various naturally occurring as well as artificially induced hybrid, polyploid, and clonal biotypes. This review aims to organize the results from previous works that used the dojo loach as the model animal for a better understanding of the interrelationship among the constitution of chromosome sets, the meiotic configuration, and the resultant gametogenesis. Autopolyploids with an even number of extra sets of homologous chromosomes were observed to be fertile. However, autopolyploids with an odd number of extra sets of homologous chromosomes and allopolyploids (polyploid hybrids) with exotic non-homologous chromosomes were found to exhibit a broad range of sterility ranging from retarded gonadal development to the production of aneuploid gametes with various abnormal characteristics. Sterile biotypes often showed meiotic configurations, including univalents. Past hybridization events likely triggered the atypical reproduction phenomena, such as the formation of unreduced isogenic gametes by doubling each chromosome for sister chromosome pairing, the elimination of a non-homologous chromosome set by meiotic hybridogenesis, and clonal development by spontaneous gynogenesis of unreduced eggs. The results obtained by studying a series of works using the dojo loach as the model organism highlight the mechanisms of sterility in hybrids and polyploids as well as of unisexuality in isogenic clones. These results contribute to the understanding of basic and aquaculture-oriented reproductive biology and genetics in fishes.