Chill susceptible and chill tolerant Drosophila species differ in their ability to maintain ion homeostasis in the cold.
Hemolymph Na+ (A) and K+ (B) concentrations before (circles with solid black line) and immediately following 4 h at 0 °C (squares with dashed black line) in five Drosophila species (crossing lines illustrate significant interaction between species and ion concentration). Solid grey areas illustrate the magnitude effect of cold exposure on concentrations of Na+ and K+ in the hemolymph. Initial hemolymph [Na+] (before any cold exposure was experienced) was a strong predictor of cold tolerance among the five species (shown as LTe50; A–insert). Chill susceptible species suffered a loss of ion balance in the cold, as shown by the positive association between cold tolerance and the change in extracellular [K+] (Δ[K+]) following cold exposure (B–insert). All values are mean ± sem.