Annual variation in glycerol mobilization and effect of freeze rigor on post-thaw locomotion in the freeze-tolerant frog Hyla versicolor

Abstract

This study documents post-thaw recovery of jump distance and cryoprotectant mobilization in the freeze-tolerant frog Hyla versicolor over two successive years. Cold acclimated frogs had plasma glycerol levels near 1.0 mM in 2004 but it was nearly 70x higher during 2005. Freezing of frogs induced nearly identical levels of plasma glycerol (ca. 177 mM) during 2004 and 2005. Plasma glucose was only mobilized upon somatic freezing, with averages ranging between 21 and 36 mM. Control jump distance showed no difference between the two years of the study. The post-thaw jump response was identical during the first 2 years despite large differences in glycerol mobilization between these 2 years. Recovery proceeded much faster in 2005 when frogs mobilized glycerol prior to freeze exposure. Frogs were more impaired in their locomotion performance during the initial stages of recovery period when they were frozen at a lower temperature (-3 vs. -1.5 degrees C) but they eventually recovered. Moderate lengthening of the freeze duration (3 vs. 7 days) with the 2004 collection group did not affect recovery of jump distance when frogs were frozen at -1.5 degrees C. Hence, postfreeze impairment of locomotion is dependent of the intensity of the freeze temperature but it is a reversible process that is mitigated when glycerol is more freely distributed to body tissues.