Reestablishment of ion homeostasis during chill-coma recovery in the cricketGryllus 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.ionoregulation | metabolism | osmotic homeostasis | thermal limits | stress resistance

Insect capa neuropeptides impact desiccation and cold tolerance

“…Several studies suggest that cold tolerance is mediated by ion and water movements in insect gut (12,16) and/or muscle (13,44). At low temperatures, ion and water homeostasis is disrupted by reduced active transport by ion-motive ATPases.…”

“…V-ATPase sets up a proton gradient, which then drives Na + and K + excretion through one or more exchangers such as sodium/proton exchanger (NHA) 1 and 2 (39). Thus, we propose that activation of capa signaling mediates recovery from nonlethal chill coma either by minimizing ion and water dysregulation during cold or by stimulating the redistribution of ions and water via the diuretic action of capa peptides on the tubule during recovery, or by both mechanisms (12). Therefore, we tested the possibility that capa-induced ion transport via VATPase and NHA1 mediates recovery from chilling injury by assessing CCR in a V-ATPase subunit mutant, vha55 (40), and an nha1 mutant.…”

“…6A), suggesting that functional capa/capaR signaling in Malpighian tubules is necessary for CCR. Recent work indicates that CCR is influenced primarily by the magnitude of ion disruption in the gut during cold exposure and the time taken to restore ion and water balance to regain motor control, potentially via ion-motive epithelial ATPases (12). Vacuolar H + -ATPase (V-ATPase) is most highly expressed in Malpighian tubule principal cells (37), which also uniquely express capaR (25).…”

“…4), and all lines showed a substantial increase in survival following RCH. For CCR experiments, capa-knockdown flies and parental lines were subject to different exposure times (4,8,12,16,20, and 24 h) and were assessed for recovery (Fig. 5A).…”

“…Recent work has demonstrated that disrupted ion and water gradients between the insect gut and hemocoel contribute to lowtemperature injury and that osmotic balance must be restored following exposure to cold (11)(12)(13). Ion and water balance in insects is regulated by the balance between excretion by the Malpighian tubules and absorption by the midgut and hindgut/rectum (14).…”