Evidence for intraspecific variation of salinity tolerance in zooplankton collected from lakes of differing salinities on the Great Plains

The Great Plains are expected to become drier over the coming decades as droughts caused by natural variation in precipitation are exacerbated by climate change. The resulting increases in lake salinity may impact biodiversity, including zooplankton. To better understand how salinity changes will affect zooplankton, our study evaluated intraspecific differences in salinity tolerance of zooplankton originating from lakes with differing salinity levels. Three species, including Ceriodaphnia laticaudata, Daphnia magna, and Daphnia schodleri, were collected from lakes near Saskatoon, Saskatchewan, and were subjected to acute salinity tolerance tests. The 24 and 48 h half-effective concentration (EC50) results for all three species were significantly lower for cultures originating from lower salinity lakes. This provides evidence that the osmoregulatory capacity of some zooplankton species may change through evolution or acclimation. This intraspecific variation in salinity tolerance among lakes in combination with dispersal may provide a source of salinity-tolerant colonists for lakes experiencing salinity increases as the climate changes, thereby lessening the effects of drought on community composition.