Osmotic and metabolic responses to cold acclimation and acute cold challenge in a freeze avoidant lizard, Podarcis siculus

• Published in: Comparative biochemistry and physiology. Part A, Molecular & integrative physiology Vol. 283; p. 111471
• Main Authors: Wohlgemuth, Ross Paul, Haro, Daniel, Liwanag, Heather E.M.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01.09.2023
• Subjects: Freeze avoidance; Italian Wall Lizard; Lacertid; Metabolic rate; Metabolism; Plasma glucose; Plasma osmolality; Respiratory exchange ratio; Respirometry; Supercooling; Metabolic rate; Respiratory exchange ratio; Respirometry; Plasma glucose; Freeze avoidance; Plasma osmolality; Supercooling; Metabolism; Lacertid; Italian Wall Lizard
• ISSN: 1095-6433; 1531-4332
• DOI: 10.1016/j.cbpa.2023.111471

Ectotherms survive exposure to subzero temperatures through freeze tolerance or freeze avoidance. Among vertebrate ectotherms, glucose is commonly used as a cryoprotectant in freeze tolerant strategies and as an osmolyte in freeze avoidant strategies, while also functioning as a metabolic substrate. Whereas some lizard species are capable of both freeze tolerance and freeze avoidance, Podarcis siculus is limited to freeze avoidance through supercooling. We hypothesized that, even in a freeze-avoidant species such as P. siculus, plasma glucose would accumulate with cold acclimation and would increase in response to acute exposure to subzero temperatures. To investigate this, we tested whether plasma glucose concentration and osmolality would increase in response to a subzero cold challenge before and after cold acclimation. In addition, we examined the relationship between metabolic rate, cold acclimation, and glucose by measuring metabolic rate during the cold challenge trials. We found that plasma glucose increased during the cold challenge trials, and that the increase was more pronounced after cold acclimation. However, baseline plasma glucose decreased throughout cold acclimation. Interestingly, total plasma osmolality did not change, and the increase in glucose only slightly altered freezing point depression. Metabolic rate during the cold challenge decreased after cold acclimation, and changes in respiratory exchange ratio suggest an increased relative use of carbohydrates. Overall, our findings demonstrate an important role for glucose in the response of P. siculus to an acute cold challenge, thus adding evidence for glucose as an important molecule for overwintering ectotherms that use freeze avoidant strategies. [Display omitted] •P. siculus does not accumulate plasma glucose or cryoprotectants during cold acclimation.•P. siculus increases plasma glucose, but not plasma osmolality in response to an acute cold challenge.•P. siculus decreases respiratory metabolism following cold acclimation.•P. siculus increases respiratory exchange ratio following cold acclimation.