Dynamic integration and evolutionary trajectory of endogenous IHHNV elements in crustacean genomes

Endogenous viral elements (EVEs) serve as molecular fossils that record the ancient co-evolutionary arms race between viruses and their hosts. In this study, by analyzing 105 host crustacean genomes, we identified 252 infectious hypodermal and haematopoietic necrosis virus-derived EVEs (IHHNV-EVEs), which include 183 ancient and 6 recently inserted EVEs. These IHHNV-EVEs are widely distributed among Decapoda, Thoracica, and Isopoda, with some of them exhibiting a syntenic distribution relative to neighboring host sequences, suggesting that the IHHNV or its ancestor are potential pathogens of these species with a long-time dynamic interaction during the evolutionary history. An expansion of IHHNV-EVEs was observed in decapoda genomes, reflecting a reinforced arm race between decapoda and IHHNV. Notably, we found that nearly all recent IHHNV-EVEs were laboratory contaminants, except for a single authentic integration in Penaeus monodon that persists intact across 16 samples from the 2 populations. These temporal dynamics-ancient genomic stabilization versus modern colonization activity-highlight that EVEs serve as dual archives: historical records of past conflicts and active participants in current evolutionary battles. Our findings redefine viral genomic colonization as a continuum, where ancient EVE fixation coexists with persistent integration processes, providing new insights into host-virus co-evolutionary trajectories.