Identification of five picorna-like viruses associated with the endangered cave-dwelling bivalve Congeria kusceri (Bole, 1962)

Congeria kusceri is a bivalve mollusk species endemic to the Dinaric Karst, which displays unique adaptations that have allowed its survival in the subterranean environment with small morphological changes compared with its fossil relatives. Anthropic activities have recently impacted the surface flow of the Neretva river, impairing the seasonal water cycle that has characterized the habitat of this species for hundreds of thousands of years. The lack of an adequate water supply, together with pollution from agricultural and farm water runoff, are posing a serious threat to C. kusceri, as evidenced by the sharp population decline observed in several locations during the past few decades. Due to the limited knowledge available about the basic biology of this filter-feeding species, the precise factors that may affect its health status and reproduction and therefore represent a hazard for its conservation are still unclear. Here, through a transcriptomic approach, we describe the nearly-complete genomes of five C. kusceri-associated RNA viruses belonging to the Picornaviridae family and phylogenetically related with picorna-like viruses previously described in other Mollusca. Although it is presently unknown whether these viruses may have a detrimental effect on bivalve health, we observed a significant increase of viral load during the summer season