Freeze tolerance evolution among anurans: Frequency and timing of appearance.

Despite numerous mechanistic studies on physiological responses supporting freeze tolerance in anurans, few have addressed the evolutionary significance of this trait. We thus investigated the phylogenetic relationships among anuran species whose freeze tolerance has been assessed and in combination with new data on freezing tolerance of two closely related species of the European brown frogs (Rana temporaria and Rana dalmatina). The species we studied exhibited short survival times in frozen state (around 8 h for both species).

Survival and metabolism of Rana arvalis during freezing.

Freeze tolerance and changes in metabolism during freezing were investigated in the moor frog (Rana arvalis) under laboratory conditions. The data show for the first time a well-developed freeze tolerance in juveniles of a European frog capable of surviving a freezing exposure of about 72 h with a final body temperature of -3 degrees C. A biochemical analysis showed an increase in liver and muscle glucose in response to freezing (respectively, 14-fold and 4-fold between 4 and -1 degrees C).

Reptilian uncoupling protein: functionality and expression in sub-zero temperatures.

Here we report the partial nucleotide sequence of a reptilian uncoupling protein (repUCP) gene from the European common lizard (Lacerta vivipara). Overlapping sequence analysis reveals that the protein shows 55%, 72% and 77% sequence homology with rat UCP1, UCP2 and UCP3, respectively, and 73% with bird and fish UCPs. RepUCP gene expression was ubiquitously detected in 4 degrees C cold-acclimated lizard tissues and upregulated in muscle tissues by a 20 h exposure to sub-zero temperatures in a supercooling state or after thawing.

Oxidative DNA damage and antioxidant defenses in the European common lizard (Lacerta vivipara) in supercooled and frozen states.

The European common lizard (Lacerta vivipara) tolerates long periods at sub-zero temperatures, either in the supercooled or the frozen state. Both physiological conditions limit oxygen availability to tissues, compelling lizards to cope with potential oxidative stress during the transition from ischemic/anoxic conditions to reperfusion with aerated blood during recovery. To determine whether antioxidant defenses are implicated in the survival of lizards when facing sub-zero temperatures, we monitored the activities of antioxidant enzymes and oxidative stress either during supercooling or during freezing exposures (20 h at -2.

Freezing tolerance of the European water frogs: the good, the bad, and the ugly.

Survival and some physiological responses to freezing were investigated in three European water frogs (Rana lessonae, Rana ridibunda, and their hybridogen Rana esculenta). The three species exhibited different survival times during freezing (from 10 h for R. lessonae to 20 h for R.

Survival and metabolic responses to freezing by the water frog (Rana ridibunda).

We studied the ability of the marsh frog Rana ridibunda to survive freezing exposure and the associated subsequent metabolic variations. This species that typically overwinters under water tolerates the conversion of 55% of its body water into ice. This ice content is attained after a few hours (between 8 and 36 hours depending on the mass of the individual and the environmental temperature) but death occurs at greater than 58% ice.

Ontogeny of thermoregulatory mechanisms in king penguin chicks (Aptenodytes patagonicus).

The rapid maturation of thermoregulatory mechanisms may be of critical importance for optimising chick growth and survival and parental energy investment under harsh climatic conditions. The ontogeny of thermoregulatory mechanisms was studied in growing king penguin chicks from hatching to the full emancipation observed at 1 month of age in the sub-Antarctic area (Crozet Archipelago). Newly hatched chicks showed small, but significant regulatory thermogenesis (21% rise in heat production assessed by indirect calorimetry), but rapidly became hypothermic.