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Genome size (C-value) and the percentage of adenine and thymine nucleotides in the genome (AT content) are fundamental characteristics of every species, and very important parameters in molecular cytogenetic and phylogenic studies, and for the progress of whole-genome sequencing. In this study, the C-value and AT content of nine abalone species inhabiting the Northwest Pacific (around Japan), Southeast Asia, South Africa, and Oceania were determined using flow cytometry. C-value ranged from 1.32 pg for Haliotis varia (Southeast Asia) to 2.01 pg for Haliotis laevigata (Oceania), and AT content ranged from 58.0% for Haliotis planata (Southeast Asia) to 66.3% for Haliotis diversicolor aquatilis (Southeast Asia). Reported chromosome numbers ranged from 2n = 32 to 36, and were higher in Oceanian, South African, and Northwest Pacific species (2n = 36) compared with the Southeast Asian group (2n = 32). This increase of chromosome number in the Oceanian species seems to be related to an increase in the DNA amount, unlike that of Haliotis midae (South African species). An increase of the C-value associated with an increase in DNA amount was also shown in the North Pacific group. These results suggest that increases in the DNA amount occurred independently in the ancestor of each of the different lineages.KEY WORDS: abalone, C-value, chromosome number, radiation, Pacific, Haliotis, INTRODUCTIONGenome size (C-value) is a fundamental characteristic of every species and is very important for the progress of molecular cytogenetic and phylogenic studies and for whole-genome sequencing. Changes in DNA [...]

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. [ABSTRACT FROM AUTHOR]

There are 2 genetically divergent groups in the dojo loach Misgurnus anguillicaudatus: A and B. Although most wild-type diploids reproduce sexually, clonal diploids (clonal loach) reproduce gynogenetically in certain areas. Clonal loaches produce unreduced isogenic eggs by premeiotic endomitosis, and such diploid eggs develop gynogenetically following activation by the sperm of sympatric wild-type diploids. These clonal loaches have presumably arisen from past hybridization events between 2 different ancestors. The genomic differences between these 2 groups have not been completely elucidated. Thus, new genetic and cytogenetic markers are required to distinguish between these 2 groups. Here, we compared the 5S rDNA region to develop markers for the identification of different dojo loach groups. The nontranscribed sequence (NTS) of the 5S rDNA was highly polymorphic and group-specific. NTSs were found in clades of 2 different groups in clonal loaches. In contrast, we did not find any group-specific sequences in the coding region of the 5S rRNA gene. Sequences were located near the centromere of the short arm of the largest submetacentric chromosomes in groups A and B and clonal loaches. Thus, the 5S rDNA of the dojo loach is conserved at the chromosomal location. Whereas, the sequences of the NTS regions evolved group-specifically in the dojo loach, with the sequences of both groups being conserved in clonal loaches. [ABSTRACT FROM AUTHOR]