Ion and water balance in Gryllus crickets during the first twelve hours of cold exposure

• Insects lose water and ion balance rapidly during chilling.
• Patterns of hemolymph [Na+] in early coma differ from those in late chill coma.
• A rise in hemolymph Na+ in the first hour of chilling may result from tissue leak.
• Hemolymph [K+] increased during chilling but did not account for paralysis.
• Chill-tolerant crickets did not defend homeostasis better during 12 h of chilling.

Insects lose ion and water balance during chilling, but the mechanisms underlying this phenomenon are based on patterns of ion and water balance observed in the later stages of cold exposure (12 or more hours). Here we quantified the distribution of ions and water in the hemolymph, muscle, and gut in adult Gryllus field crickets during the first 12 h of cold exposure to test mechanistic hypotheses about why homeostasis is lost in the cold, and how chill-tolerant insects might maintain homeostasis to lower temperatures. Unlike in later chill coma, hemolymph [Na+] and Na+ content in the first few hours of chilling actually increased. Patterns of Na+ balance suggest that Na+ migrates from the tissues to the gut lumen via the hemolymph. Imbalance of [K+] progressed gradually over 12 h and could not explain chill coma onset (a finding consistent with recent studies), nor did it predict survival or injury following 48 h of chilling. Gryllus veletis avoided shifts in muscle and hemolymph ion content better than Gryllus pennsylvanicus (which is less chill-tolerant), however neither species defended water, [Na+], or [K+] balance during the first 12 h of chilling. Gryllus veletis better maintained balance of Na+ content and may therefore have greater tissue resistance to ion leak during cold exposure, which could partially explain faster chill coma recovery for that species.

Figure optionsDownload as PowerPoint slide