Clone-specific cytogenetic features revealed by a new repetitive marker in dojo loach

Most fish reproduce sexually, but some species reproduce asexually through gynogenesis. Gynogenetic species are thought to provide important insight into the evolution of sexual reproduction, and investigations into their origins are required. Clonal loaches exist in certain areas of Japan and may have resulted from a past hybridization event between the two genetically divergent groups (A and B). However, the intergroup hybrids between current groups A and B show reproduce the patterns different from those of clonal loaches, and comparisons distinguish the ancestral group within clonal loaches from the current group are needed.

We used NGS data to search for repetitive sequences that could serve as markers to reveal genetic differences between species and populations and developed new cytogenetic marker, M407.

The karyotypes and 18S rDNA signals were conserved across all examined individuals. M407 signals were detected in group B and in the ancestral groups A and B of clonal loaches, but not in the current group A.

Cytogenetic results suggest that sequences associated with group B may have been introgressed or structurally incorporated into the ancestral group A genome during hybridization events leading to the formation of clonal loaches.