Claude Grenot

Supercooling, ice inoculation and freeze tolerance in the European common lizard, Lacerta vivipara

The European common lizard (Lacerta vivipara) is widely distributed throughout Eurasia and is one of the few Palaearctic reptiles occurring above the Arctic Circle. We investigated the cold-hardiness of L. vivipara from France which routinely encounter subzero temperatures within their shallow hibernation burrows. In the laboratory, cold-acclimated lizards exposed to subfreezing temperatures as low as -3.5°C could remain unfrozen (supercooled) for at least 3 weeks so long as their microenvironment was dry. In contrast, specimens cooled in contact with ambient ice crystals began to freeze within several hours. However, such susceptibility to inoculative freezing was not necessarily deleterious since L. vivipara readily tolerated the freezing of its tissues, with body surface temperatures as low as -3.0°C during trials lasting up to 3 days. Freezing survival was promoted by relatively low post-nucleation cooling rates (≤0.1°C·h-1) and apparently was associated with an accumulation of the putative cryoprotectant, glucose. The cold-hardiness strategy of L. vivipara may depend on both supercooling and freeze tolerance capacities, since this combination would afford the greatest likelihood of surviving winter in its dynamic thermal and hydric microenvironment.

How does the European common lizard, Lacerta vivipara, survive the cold of winter?

Although the European common lizard, Lacerta vivipara, is among the most common Eurasian reptile species, we know little about how these lizards cope with very low temperatures. In this study we examined microenvironmental conditions, body temperature, behavior, and cold strategies to see whether strategies of freezing and supercooling, while normally considered to be mutually exclusive, may in fact be adopted simultaneously by the common lizard. Following up on an earlier study of a lowland population, this time we used a mountain population (850 m) to discover differences in overwintering strategies between the two populations. Differential scanning calorimetry conducted during the hibernation period (vs. the activity period) showed that the blood of highland lizards had an increased ability to resist ice formation, confirming an ecophysiological effect most likely mediated by physical properties of the blood. Mean blood glucose level of unfrozen L. vivipara in the field increased significantly (about fourfold) from 8.5+/-0.7 mmol l(-1) in September to 33.2+/-5.6 mmol l(-1) in March. The blood glucose level then experienced a significant decline as it fell to 6. 2+/-0.8 mmol l(-1) after hibernation in April. Glucose, in conclusion, seems to play a role of cryoprotectant rather than antifreeze.

Aldosterone and the control of secretion by the nasal salt gland of the north African desert lizard, Uromastix acanthinurus.

The secretory response of the nasal salt gland of the north African agamid lizard Uromastix acanthinurus to injections of 1 M KCl and NaCl is correlated with changes in circulating levels of the corticosteroids aldosterone and corticosterone. KCl loading led to a progressive rise in plasma aldosterone levels, and NaCl loading was associated with a fall. Neither treatment significantly altered plasma corticosterone concentrations which remained at levels characteristic of unstressed animals. Rates of potassium excretion were positively correlated with circulating levels of aldosterone whereas sodium excretion showed a negative correlation. As in previous studies, injections of exogenous aldosterone or dexamethasone into KCl-loaded animals failed to further stimulate potassium excretion, but did depress sodium excretion by the gland. Spironolactone, an aldosterone antagonist in mammals, was without effect on the rate of potassium excretion in KCl-injected animals. These data suggest that aldosterone functions as a mineralocorticoid on the nasal gland of U. acanthinurus (i.e., natriferic and kaliuretic) but direct evidence of this will require the use of adrenalectomized animals.

Metabolic adaptations of overwintering European common lizards (Lacerta vivipara).

The European common lizard Lacerta vivipara, a reptile of cold‐temperate climates, provides us an interesting model of low‐temperature adaptation. Indeed its unique cold‐hardiness strategy, which employs both freeze tolerance and freeze avoidance, may be seen as the primary reason for its large distribution, which extends from Spain to beyond the Arctic circle. To study the metabolism supporting this capacity, we used three techniques: two techniques of calorimetry (oxygen consumption and thermogenesis) and nuclear magnetic resonance spectroscopy. These techniques were used to examine the metabolic balance and the different molecular pathways used between three different periods through the year (September, January, and May). The results show a significant 20% augmentation of winter anaerobic metabolism compared to other periods of the year. This is mainly because of an activation of the lactic fermentation pathway leading to an increase of lactate concentration (>34% in winter). Furthermore, glucose, which increases some 245% in winter, is used as antifreeze and metabolic substrate. Furthermore, this study provides evidence that the physiological adaptations of the common lizard differ from those of other ectotherms such as Rana sylvatica. Concentrations of alanine and glycerol, commonly used as antifreeze by many overwintering ectotherms, do not increase during winter.

Temperature regulation in the tortoise Testudo hermanni, studied with indwelling probes

Behavioural thermoregulation has been studied in the terrestrial tortoise Testudo hermanni in south-eastern France by implanting temperature-sensitive probes in free-ranging individuals. Three tortoises were monitored over a period of nine months (July to March); they maintained body temperatures close to their preferendum for periods of several hours each day. These results are of interest as doubt has been expressed in the literature on the thermoregulatory capacities of Testudo hermanni in the northernmost part of its range.

Variation of plasma sex steroid concentrations in wild and captive populations of Hermann’s tortoise (Testudo hermanni hermanni) in Southern France

Plasma levels of sex steroids in both males and females of the endangered Hermanns tortoise (Testudo hermanni hermanni) were measured throughout their active period in a wild population in the Massif des Maures, France, and in a nearby captive population at Le Village des Tortues in Gonfaron. Both plasma progesterone and testosterone were elevated in males at emergence from winter dormancy, and plasma progesterone levels were significantly higher in wild than in captive males. Plasma testosterone in males then fell to the lowest levels (10 ng ml(-1)) during the nesting season from April to June followed by an elevated plateau during summer, with levels reaching 80 ng ml(-1), presumably concomitant with spermiogenesis. Plasma testosterone increased in all females during autumn, an indication of follicular growth, and remained high on emergence from hibernation, to peak during April, although levels were lower in the captive population. Plasma progesterone also peaked during April and May, presumably related to ovulation, but, again, these changes were less marked in the captive than in the wild females. Measurements of testosterone, progesterone and 17beta-oestradiol in the captive females during their period of oviposition in spring suggested that some females did ovulate and lay eggs, whereas others did not. Differences in sex steroid levels between captive and wild populations of Hermanns tortoise may indicate a problem with ovulation and/or with stress in a proportion of captive females.

Water and electrolyte balance of free-living Saharan lizards,Uromastix acanthinurus (Agamidae)

SummaryChanges in body condition ofUromastix acanthinurus are closely related to climatic factors and influenced by habitat vegetation.1.The body mass index decreases significantly during the dry season and the contents of the digestive tract are responsible for most of these variations.2.U. acanthinurus achieves a large total body water volume (75.4% adjusted body mass) by accumulating extracellular fluid (33% body mass) and maintains a normal level of hydration during the dry season. Total body water decreases during this period (due essentially to diminution of extracellular fluid) but blood volume and plasma volume are almost unaffected.3.During spring there is an increase in body solids, essentially as fat reserves.4.The electrolyte balance also exhibits seasonal variations. Plasma sodium concentration increases significantly during the dry period, in relation to the decrease of extracellular fluid. Return to normal values after rainfall results from intake of a diet low in sodium. Plasma potassium shows only random variation and appears to be regulated by excretion via the nasal salt gland and in cloacal pellets.5.Under field conditions, changes in the internal environment appear more pronounced in the Saharan Agamid,Uromastix acanthinurus than in its analog, the North American Iguanid,Sauromalus obesus.

Field metabolism of lizards from lower altitude regions of Baja California Sur (Mexico)

Water flux rate and field metabolic rate of three free-ranging sympatric species of lizards (Uta stansburiana, Urosaurus nigricaudus and Cnemidophorus hyperythrus) were measured in the Cape Region, near La Paz (Baja California Sur, Mexico) using labelled water ( 3 H 2 O and H 2 18 O). During the rainy season, the three species consumed the same prey. Caterpillars of Lepidoptera (7.1 ml H 2 O/g DM) were the most important in volume and mass. The lizards showed high water flux rates, which did not differ from those of non-desert species, but were 2 to 7 times higher than during the dry season. During the dry season the low rates of water flux were basically due to low metabolic rates. The water flux rate of C. hyperythrus in September was two to four times higher than rates in two other populations in the southern part of the Cape region, but the field metabolic rate was similar. Adult size in the El Comitan population (BM = 6.3 g) was larger than that in two Cabo San Lucas populations (BM = 4.4 and 3.9 g). These data suggest flexibility of responses of species and populations to environmental variation.