Effect of temperature acclimation on haemolymph composition in the freeze-tolerant larvae of Eurosta solidaginis

Abstract

The physiological and biochemical composition of haemolymph from warm (23°C) and cold (3°C) acclimated E. solidaginis larvae was assessed in a search for haemolymph adaptations for freeze tolerance. Haemolymph pH and total carbon dioxide content did not vary between the two groups although the effect of temperature on pH ( ΔpH ΔT ) was higher for warm acclimated (−0.0142 U/°C) than for cold acclimated (−0.0116 U/°C) larvae. Haemolymph from cold-acclimated larvae had a 2-fold higher Mg 2+ content and was also higher in Na + and Ca 2+ but lower in K + than haemolymph from warm-acclimated larvae. Both groups accumulated cryoprotectants over the course of acclimation, glycerol in warm acclimated and glycerol + sorbitol in cold-acclimated larvae, with equal hydroxyl equivalents achieved in the two groups but a higher osmolarity in the haemolymph of the warm-acclimated larvae. Citrate content of the haemolymph was 48% higher in cold-acclimated larvae. Contents of polyols, sugars, organic acids, amino acids and protein were also measured in whole larvae and comparisons with haemolymph levels revealed that polyols, organic acids and all amino acids except glutamate were probably in equilibrium between intra- and extracellular fluids while sugars (glucose, fructose) were preferentially concentrated in the haemolymph and protein content was higher in cells. Amino acid composition varied between warm and cold-acclimated larvae with the larger pool, due to a higher proline content, in the haemolymph of warm-acclimated animals. Concentrations of several neutral amino acids (threonine, serine, glycine, valine) were higher in the haemolymph of cold-acclimated larvae while levels of charged amino acids (asparagine, arginine) were lower.