Fig. 3. Fold-change in Na⁺/K⁺-ATPase _1a mRNA expression (N>7) (A) as well as Na⁺/K⁺-ATPase activity (N>6) in northern (B) and southern (C) killifish gills before (pre) and after transfer from brackish water (BW; 10 g l^-1; squares) to either brackish water or freshwater (FW; triangles). Expression data are standardized to elongation factor 1 and are relative to time-matched brackish water controls (see Materials and methods). Data are expressed as means ± S.E.M. ^*Significant difference from time-matched brackish water control. Significant difference from northern population (P<0.05). Data for northern killifish are from Scott et al. (2004).