# Repeatome Dynamics and Sex Chromosome Differentiation in the XY and XY1Y2 Systems of the Fish Hoplias malabaricus (Teleostei; Characiformes)

## TL;DR

This study explores the sex chromosome systems in the fish Hoplias malabaricus, revealing similarities and differences in their genomic composition and repeatome dynamics.

## Contribution

The study provides new insights into the genomic and repeatome dynamics of homologous XY and XY1Y2 sex chromosome systems in a single fish species.

## Key findings

- Both XY and XY1Y2 systems show similar sex chromosome content and repeatome composition, dominated by transposable elements.
- Sex-specific sequences were identified in non-recombining regions of Y chromosomes, supported by specific satellite DNA haplotypes.
- The KarF Y chromosome corresponds to two linkage groups (Y1 and Y2) in KarG, suggesting a unique meiotic arrangement involving the X chromosome.

## Abstract

The wolf fish Hoplias malabaricus is a Neotropical species characterized by remarkable karyotypic diversity, including seven karyomorphs (KarA-G) with distinct sex chromosome systems. This study investigated the homologous XY (KarF) and XY1Y2 (KarG) sex chromosome systems present in this species by integrating cytogenetics and genomics to examine sex chromosomes’ composition through characterization of repeatome (satellite DNA and transposable elements) and sex-linked markers. Our analysis indicated that both karyomorphs are little differentiated in their sex chromosomes content revealed by satDNA mapping and putative sex-linked markers. Both repeatomes were mostly composed of transposable elements, but neither intra- (male versus female) nor interspecific (KarF x KarG) variations were found. In both systems, we demonstrated the occurrence of sex-specific sequences probably located on the non-recombining region of the Y chromosome supported by the accumulation of sex-specific haplotypes of HmfSat10-28/HmgSat31-28. This investigation offered valuable insights by highlighting the composition of homologous XY and XY1Y2 multiple sex chromosomes. Although homologous, the large Y chromosome in KarF corresponds to two separate linkage groups (Y1 and Y2) in KarG implying a specific meiotic arrangement involving the X chromosome in a meiotic trivalent chain. This scenario likely influenced recombination rates and, as a result, the genomic composition of these chromosomes.