Genome characterization, prevalence and transmission mode of a novel picornavirus associated with the Threespine Stickleback fish ( Gasterosteus aculeatus ).

The complete genome sequence of an RNA virus was assembled from RNA sequencing of virus particles purified from threespine stickleback intestine tissue samples. This new virus is most closely related to the Eel Picornavirus and can be assigned to the genus Potamipivirus in the family Picornaviridae Its unique genetic properties are enough to establish a new species, dubbed the Threespine Stickleback Picornavirus (TSPV). Due to their broad geographic distribution throughout the northern hemisphere and parallel adaptation to freshwater, threespine sticklebacks have become a model in evolutionary ecology. Further analysis using diagnostic PCRs revealed that TSPV is highly prevalent in both anadromous and freshwater populations of threespine sticklebacks, infects almost all fish tissues and is transmitted vertically to offspring obtained from in vitro fertilization in laboratory settings. Finally, TSPV was found in Sequence Read Archives of transcriptome of G. aculeatus further demonstrating its wide distribution and unsought prevalence in samples. It is thus necessary to test the impact of TSPV on the biology of threespine sticklebacks as this widespread virus could interfere with the behavioral, physiological, or immunological studies that employ this fish as model system. Abstract Importance The threespine stickleback species complex is an important model system in ecological and evolutionary studies because of the large number of isolated divergent populations that are experimentally tractable. For similar reasons, its co-evolution with the cestode parasite Schistocephalus solidus , its interaction with gut microbes, and the evolution of its immune system are of growing interest. Herein we describe the discovery of an RNA virus that infects both freshwater and anadromous populations of sticklebacks. We show that the virus is transmitted vertically in laboratory settings and found it in Sequence Read Archives suggesting that experiments using sticklebacks were conducted in presence of the virus. This discovery can serve as a reminder that the presence of viruses in wild-caught animals is possible, even when animals appear healthy. Regarding threespine sticklebacks, the impact of TSPV on the fish biology should be investigated further to ensure that it does not interfere with experimental results.