Evolutionary and acclimatory shifts in ion transporter gene expression across salinity transitions in the copepod Eurytemora carolleeae

In the copepod Eurytemora carolleeae, 19 ion transporter genes show paralog-specific evolutionary shifts across saline-to-freshwater transitions, including increased freshwater expression for NKA--1 and NKCC-3.

• Why it matters: Salinity transitions challenge ionic homeostasis, and invaders must acclimate or evolve to survive. This work targets how ion transporter gene expression changes during such boundary crossings.
• What they did: Using quantitative real-time PCR, the study compared ancestral saline versus derived freshwater populations in a common garden reaction norm and a laboratory natural selection experiment, focusing on 19 ion transport-related genes. It tested evolutionary and acclimatory shifts in paralogs including NKA--1, NKCC-3, NHA-7, and NHA-5.
• The result: NKA--1 and NKCC-3 evolved increased freshwater expression across all conditions, while NHA-7 and NHA-5 evolved elevated saline expression under low salinity; plasticity also differed, with freshwater populations comparatively canalized. In the selection experiment, NKCC-3, NHA-5, and NHA-7 largely recapitulated natural evolutionary shifts, whereas the freshwater selection line showed little response during salinity increase.

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