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Largest Stonefly in the Western U.S.

Pteronarcys californica is a member of the stonefly family Pteronarcyidae and is commonly referred to as the giant salmonfly by anglers. P. californica is the largest species of stonefly in the western United States and is of ecological, cultural, and economical importance. Their large body size (>6 cm in length) makes them an essential prey item for aquatic consumers like fish, and their highly synchronous emergence to adulthood provides an important seasonal food resource for terrestrial consumers, including birds, spiders, amphibians, and small mammals.

Stoneflies are indicators of freshwater quality and mediate nutrient cycling and energy flow. Most stoneflies are stenothermic, meaning they are only able to survive within a narrow temperature range and are generally susceptible to warming. Because of their environmental sensitivity, they are a focal macroinvertebrate group for aquatic biomonitoring.

Pteronarcys californica – the giant salmonfly. Photo credits – Anna Eichert

Giant salmonfly populations have experienced a substantial decline in the past few decades – becoming regionally extinct in numerous rivers in Utah, Colorado, and Montana. They are incredibly sensitive to pollution, warming temperatures, flow modification, land-use change, sedimentation, and other environmental stressors on energy flows. Ecological variables pertaining to the subsistence of giant salmonfly populations have been well-recorded, but the genomic features of this species (or family) had not been explored before this.


The chromosome-length genome assembly shared today was generated using a flash-frozen individual collected from the Diamond Fork River in Utah, provided by PhD candidate Anna Eichert at the American Museum of Natural History. See the DNAZoo Methods page for more details on the procedure and check out the interactive contact map below and on the assembly page. This genome is a Hi-C upgrade of a PacBio draft generated with help from Dr. Paul Frandsen at Brigham Young University (BYU) and the BYU DNA Sequencing Center. We thank Drs. Jessica Ware, Scott Hotaling, and C. Riley Nelson for their assistance with the analyses, providing funding to complete this project, and for their general support.

Conservation attention is immediately required to prevent P. californica from going extinct. Because P. californica has adapted to fast-flowing rivers with historical temperature and flow regimes that are now being altered by human activity in many different ways, there is limited habitat availability for these essential insects. With this being only the 9th genome produced for stoneflies, stonefly genomics is an emerging field of study. Genetic tools will provide more information on the evolutionary responses of stoneflies to habitat alteration. This, in combination with environmental data, can provide structure to prompt conservation efforts.


We hope to continually raise awareness of the ecological importance of this species in freshwater environments and rally for resources to aid in their preservation. We support and commend the work of organizations such as The Salmonfly Project that aim to monitor and generate population data for P. californica in the western United States (see for more information).

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