title: Reestablishment of ion homeostasis during chill-coma recovery in the cricket Gryllus pennsylvanicus.
abstract: The time required to recover from cold-induced paralysis (chill-coma) is a common measure of insect cold tolerance used to test central questions in thermal biology and predict the effects of climate change on insect populations. The onset of chill-coma in the fall field cricket (Gryllus pennsylvanicus, Orthoptera: Gryllidae) is accompanied by a progressive drift of Na(+) and water from the hemolymph to the gut, but the physiological mechanisms underlying recovery from chill-coma are not understood for any insect. Using a combination of gravimetric methods and atomic absorption spectroscopy, we demonstrate that recovery from chill-coma involves a reestablishment of hemolymph ion content and volume driven by removal of Na(+) and water from the gut. Recovery is associated with a transient elevation of metabolic rate, the time span of which increases with increasing cold exposure duration and closely matches the duration of complete osmotic recovery. Thus, complete recovery from chill-coma is metabolically costly and encompasses a longer period than is required for the recovery of muscle potentials and movement. These findings provide evidence that physiological mechanisms of hemolymph ion content and volume regulation, such as ion-motive ATPase activity, are instrumental in chill-coma recovery and may underlie natural variation in insect cold tolerance.
authors.affiliation: Department of Biology, University of Western Ontario, London, ON, Canada N6A 5B7. hmacmil2@uwo.ca
authors.forename: Heath A
authors.initials: HA
authors.lastname: MacMillan
authors.forename: Caroline M
authors.initials: CM
authors.lastname: Williams
authors.forename: James F
authors.initials: JF
authors.lastname: Staples
authors.forename: Brent J
authors.initials: BJ
authors.lastname: Sinclair
mesh_terms: D000064:Acclimatization / Q000502:physiology; D000818:Animals; D003081:Cold Climate; D004068:Digestive System Physiological Phenomena; D005260:Female; D006135:Gryllidae / Q000502:physiology*; D006458:Hemolymph / Q000502:physiology; D006706:Homeostasis; D017136:Ion Transport; D008954:Models, Biological; D009119:Muscle Contraction / Q000502:physiology; D011188:Potassium / Q000378:metabolism; D012964:Sodium / Q000378:metabolism; D014882:Water-Electrolyte Balance
chemical_list: D012964:Sodium; D011188:Potassium