Christelle Rutz

Background: Repetitive elements, particularly satellite DNA (satDNA), play a significant role in genome evolution and organisation. However, their diversity and evolutionary dynamics remain poorly understood in non-model organisms. Freshwater crayfish (Decapoda, Astacidea) have large genomes with a high chromosome number and are rich in satDNAs. This makes them attractive for studying the impact of satDNA on genome evolution. Results: In this study, we investigated the repetitive genomic landscape of 19 species representing four freshwater crayfish families. Our analysis revealed a high proportion of repetitive DNA in all studied species, with the total repeat content ranging from 30% to 66%. The number of satDNA families was remarkably high (54–622 families per species), with minisatellites (< 100 bp) forming the largest component of the satellitome. Family-specific patterns emerged: Astacidae and Cambaroididae showed the highest satDNA proportions, while Cambaridae and Parastacidae were dominated by Class I transposable elements. Species of the family Parastacidae showed the largest number of unique satDNA clusters and were clearly separated from other families, reflecting their phylogenetic divergence and distinct biogeographic history. We identified specific satDNAs conserved across all species, among them the PlSAT3-411, pointing to their important functional roles as pericentromeric satDNA. Conclusion: This study provides the first comprehensive comparative analysis of satDNA in freshwater crayfish. Our results highlight the dynamic nature of repetitive DNA and underscore its importance in genome organisation and evolutionary history.

Background: Biodiversity in freshwater ecosystems is declining due to an increased anthropogenic footprint. Freshwater crayfish are keystone species in freshwater ecosystems and play a crucial role in shaping the structure and function of their habitats. The Idle Crayfish Austropotamobius bihariensis is a native European species with a narrow distribution range, endemic to the Apuseni Mountains (Romania). Although its area is small, the populations are anthropogenically fragmented. In this context, the assessment of its conservation status is timely. Results: Using a reduced representation sequencing approach, we identified 4875 genomic SNPs from individuals belonging to 13 populations across the species distribution range. Subsequent population genomic analyses highlighted low heterozygosity levels, low number of private alleles and small effective population size. Our structuring analyses revealed that the genomic similarity of the populations is conserved within the river basins. Conclusion: Genomic SNPs represented excellent tools to gain insights into intraspecific genomic diversity and population structure of the Idle Crayfish. Our study highlighted that the analysed populations are at risk due to their limited genetic diversity, which makes them extremely vulnerable to environmental alterations. Thus, our results emphasize the need for conservation measures and can be used as a baseline to establish species management programs.