Freshwater Mussels Show Elevated Viral Richness and Intensity during a Mortality Event

Area of Science:

• * Aquatic Ecology
• * Virology
• * Conservation Biology

Background:

• * Freshwater mussels (Unionida) are critically endangered globally.
• * The link between mussel mortality events and infectious disease remains poorly understood.
• * Viral pathogens are a potential, yet understudied, cause of mass mortality in freshwater mussels.

Purpose of the Study:

• * To investigate the relationship between viral infections and mortality events in freshwater mussels.
• * To compare the viromes of mussels experiencing mortality with those from healthy populations.
• * To identify potential viral contributors to mussel die-offs.

Main Methods:

• * Surveyed viromes of the mucket (Actinonaias ligamentina) in Michigan during a mortality event.
• * Compared these viromes to healthy mucket populations in Wisconsin and a diseased pheasantshell population in Tennessee/Virginia.
• * Utilized next-generation sequencing to identify and quantify viruses in mussel samples.

Main Results:

• * Identified 38 viruses, with most linked to the Michigan mortality event.
• * Significantly higher viral richness and read depth in moribund mussels compared to healthy controls.
• * Demonstrated a substantial increase in viral infections during mussel mortality events.

Conclusions:

• * Viral infections are significantly more prevalent and intense in freshwater mussels during mortality events.
• * Healthy mussel populations exhibit a restricted virome with low viral loads.
• * Findings suggest viruses play a crucial role in freshwater mussel mortality events, highlighting disease as a key factor in their imperilment.