Satellite DNA evolution in two holocentric species of Edessa true bugs (Hemiptera: Pentatomidae) with unusually high heterochromatin abundance.

Satellite DNAs (satDNAs) are a major component of eukaryotic genomes, playing key roles in chromosome organization, heterochromatin formation, and genome evolution. Although satellitomes have been increasingly characterized in insects, most studies focus on monocentric species, leaving holocentric systems comparatively understudied. Here, we investigate the satellitomes of two pentatomid bugs, Edessa meditabunda and Edessa loxdalii, which exhibit unusually large heterochromatin blocks for holocentric chromosomes. Using an integrative approach combining genome analysis and molecular cytogenetics, we identified 31 satDNA families shared between species. E. loxdalii shows higher satDNA abundance and lower sequence divergence, consistent with recent amplification and homogenization, whereas E. meditabunda exhibits lower abundance and higher divergence, suggesting more advanced sequence degeneration. SatDNA landscape analyses indicate distinct evolutionary trajectories, with evidence of multiple amplification waves and differential repeat turnover. Despite these differences, both species share a conserved set of satDNAs, including highly abundant families that dominate their satellitomes, supporting the library hypothesis. Compared to other Pentatomidae species with low heterochromatin content, there is no overall increase in satDNA abundance in Edessa, but rather amplification of specific families. Chromosomal mapping revealed that these amplified satDNAs are major components of terminal heterochromatin blocks, while less abundant families show chromosome-specific distributions, including accumulation on the Y chromosome, with signs of evolutionary differentiation between species. Overall, this study provides new insights into satellitome organization and evolution in Pentatomidae, highlighting the role of satDNAs in shaping chromosome architecture in holocentric systems.