Brine chemistry matters: Isolation by environment and by distance explain population genetic structure of Artemia franciscana in saline lakes

The American brine shrimp Artemia franciscana is important in aquaculture and has become invasive in other continents, aided by dispersal via waterbirds. However, little is known about processes underlying its genetic diversity and population structure in its natural habitat in North America. These processes, including dispersal and local adaptation, are pivotal drivers of species distribution and community structure, and therefore central to aquatic biodiversity. We studied 15 populations in natural saline lakes of Saskatchewan, Canada to determine the influence of variation in geological history, water chemistry, lake size, and location. We aimed to determine the relative importance of isolation by distance and isolation by environment using the cytochrome c oxidase subunit 1 gene (CO1) as a mitochondrial marker and five nuclear microsatellite markers. Geographic patterns for CO1 and microsatellites differed, with lakes clustering in different groups based on genetic distances according to the marker used. CO1 better indicated historical colonisation processes, suggesting potential routes of initial colonisation when lakes were formed after deglaciation 11,000-15,000 years ago. Differentiation between lakes based on nuclear markers was strongly related to variation in hydrochemistry, suggested by distance-based redundancy analysis, but there was no indication of isolation by distance. The ratio between alkalinity and the sum of Ca and Mg concentrations was particularly important, although a lake with a high Cl concentration caused by potash mining also had a unique Artemia population. Geochemistry is important in the adaptive radiation of anostracan crustaceans. Our study suggests that it also underlies intraspecific genetic variation between populations, promoting isolation by environment, and making dispersal ineffective when cysts are moved by birds between lakes with different hydrochemistry.

Automated summary

The study of Artemia franciscana populations in natural saline lakes of Saskatchewan, Canada revealed that geological history, water chemistry, lake size, and location influence genetic diversity. Mitochondrial marker CO1 indicated historical colonization processes, while nuclear markers were related to variation in hydrochemistry. Geochemistry plays a key role in intraspecific genetic variation and may promote isolation by environment, impacting dispersal via waterbirds.