Thermal tolerance of the male freshwater prawn Cryphiops caementarius exposed to different acclimation temperatures.

The variation in water temperature influences metabolic and biochemical processes in ectothermic organisms, affecting development, behavior, and thermal responses. We conducted laboratory experiments based on different acclimation temperatures to determine the thermal tolerance in male specimens of the freshwater prawn Cryphiops caementarius. During 30 days, male prawns were exposed to acclimation temperatures of 19 °C (control), 24 °C, and 28 °C treatments. The Critical Thermal Maxima (CTMax) values at these acclimation temperatures were 33.42 °C, 34.92 °C, and 36.80 °C; whereas values for the Critical Thermal Minimum (CTMin) were 9.38 °C, 10.57 °C, and 13.88 °C. All acclimation temperature treatments had a positive effect (P < 0.05) on CTMax and CTMin, with high and significant correlations (CTMax: r = 0.992, P < 0.01; CTMin: r = 0.946, P < 0.01). The area of the thermal tolerance polygon over the three acclimation temperatures was 211.32 °C2 and the acclimation response rate values were high (CTMax from 0.30 to 0.47; CTMin from 0.24 to 0.83) but similar to those from other tropical crustacean species. These results demonstrate that adult males of the freshwater prawn C. caementarius can tolerate extreme water temperatures through a thermal plasticity response, which could be advantageous during a global warming scenario.

To bask or not to bask: Behavioural thermoregulation in two species of dasyurid, Phascogale calura and Antechinomys laniger.

Torpor is an important physiological process used to reduce body temperature and thus energy needs in mammals and birds. Rewarming from torpor can be costly. In some small mammals basking is used to reduce the cost of rewarming from torpor. The use and duration of basking was measured in two native Australian marsupials, the red-tailed phascogale (Phascogale calura) and kultarr (Antechinomys laniger), using a heat rock. Animals were observed via video cameras to determine whether they used basking behaviours and whether this behaviour was affected by food availability. Both species became accustomed to the heat rock as time progressed. Absence of food increased basking duration and frequency in some individuals but not all animals. Generally kultarrs basked for longer periods than phascogales, and kultarrs would bask at all hours of the day while phascogales showed a strict nocturnal regime (1900-0700h). The results demonstrate that basking may be an important behavioural adaptation of the kultarr; while the phascogale requires further research.

Effects of unsaturated fatty acids on torpor frequency and diet selection in Djungarian hamsters (Phodopus sungorus).

Essential polyunsaturated fatty acids (PUFA) have been shown to play a beneficial role in hibernating mammals. High amounts of dietary PUFA led to an earlier hibernation onset, deeper and longer hibernation bouts and a higher proportion of hibernating animals in several species. In contrast, the relevance of dietary PUFA for daily heterotherms exhibiting only brief and shallow torpor bouts is less well studied. Therefore, diets differing in PUFA composition were used to examine the effects on the frequency of spontaneous daily torpor in Djungarian hamsters (Phodopus sungorus). In contrast to earlier studies, we were interested in whether the ratio of n-6 to n-3 PUFA affects torpor expression, and in comparison with a diet rich in monounsaturated fatty acids (MUFA). Although we found a positive effect on torpor frequency in hamsters fed a diet rich in n-6 PUFA compared with the groups fed diets either rich in n-3 PUFA or MUFA, the latter two groups did not show unusually low torpor frequencies. The results of the additional diet choice experiment indicated that hamsters in short photoperiod select food with only a slight excess of n-6 PUFA compared with n-3 PUFA (ratio of 1 to 1.5). However, there was no significant difference in torpor frequency between the diet choice group and hamsters fed on standard chow with a sevenfold excess of n-6 PUFA. In summary, the present data strongly indicate that the dietary composition of unsaturated fatty acids plays a minor role in the occurrence of spontaneous daily torpor in Djungarian hamsters.

OB-RL silencing inhibits the thermoregulatory ability of Great Roundleaf Bats (Hipposideros armiger).

Previous studies have shown that the hormone Leptin has an important role in mammalian heterothermy by regulating metabolism and food intake via lipolysis, as well as adaptive evolution of Leptin in heterothermic bats driven by selected pressure. However, the mechanism of Leptin in heterothermic regulation in mammals is unknown. By combining previous results, we speculated that the Leptin signaling pathway mediated by OB-RL (Leptin receptor long form) in the hypothalamus is important. OB-RL is one of the products of db gene and mainly distributed in the hypothalamus. In this study, we used OB-RL as a molecular marker, combining with the RNA interference technology and physiological/molecular analyses with Hipposideros armiger (a hibernating bat species) as an animal model, to explore the mechanism of Leptin in heterothermic regulation. Our data showed that all of four anti-OB-RL shRNA lentivirus significantly inhibited OB-RL expression (>90%), and the interference efficiency of PSC1742 lentivirus reached the highest value. In situ hybridization proved that PSC1742 lentivirus significantly decreased the OB-RL expression in the hypothalamus, especially in the ventromedial hypothalamic nucleus (VHM, 86.6%). Physiological analysis demonstrated that the thermoregulatory ability of bats (e.g., reducing core body temperature and heart rate) was significantly depressed after OB-RL silencing in the hypothalamus, and animals could not enter torpor state. Our study for the first time proved that the knock-down of OB-RL expression in hypothalamus inhibits heterothermic regulation of bats, and also provided the clues for further analyzing the mechanism of Leptin in the heterothermic regulation of mammals.

Shallow hypothermia depends on the level of fatty acid unsaturation in adipose and liver tissues in a tropical heterothermic primate.

Optimal levels of unsaturated fatty acids have positive impacts on the use of prolonged bouts of hypothermia in mammalian hibernators, which generally have to face low winter ambient temperatures. Unsaturated fatty acids can maintain the fluidity of fat and membrane phospholipids at low body temperatures. However, less attention has been paid to their role in the regulation of shallow hypothermia, and in tropical species, which may be challenged more by seasonal energetic and/or water shortages than by low temperatures. The present study assessed the relationship between the fatty acids content of white adipose and liver tissues and the expression of shallow hypothermia in a tropical heterothermic primate, the gray mouse lemur (Microcebus murinus). The adipose tissue is the main tissue for fat storage and the liver is involved in lipid metabolism, so both tissues were expected to influence hypothermia dependence on fatty acids. As mouse lemurs largely avoid deep hypothermia (i.e. torpor) use under standard captive conditions, the expression of hypothermia was triggered by food-restricting experimental animals. Hypothermia depth increased with time, with a stronger increase for individuals that exhibited higher contents of unsaturated fatty acids suggesting that they were more flexible in their use of hypothermia. However these same animals delayed the use of long hypothermia bouts relative to individuals with a higher level of saturated fatty acids. This study evidences for the first time that body fatty acids unsaturation levels influence the regulation of body temperature not only in cold-exposed hibernators but also in tropical, facultative heterotherms.

Patterns of nest box sharing in woodland dormice (Graphiurus murinus): Evidence for intra-sexual tolerance and communal nesting.

Nest sharing in rodents and other vertebrates is believed to be promoted by the gain of thermoregulatory advantages, reproductive imperatives or to be a by-product of other benefits to group living. Here, we studied the patterns of nest box sharing over a yearly cycle in a wild population of the arboreal, nocturnal and heterothermic woodland dormouse (Graphiurus murinus). We evaluated whether the timing of dormouse aggregations and group composition were compatible with thermoregulatory or reproductive imperatives. Nest box sharing between two or more dormice was observed throughout the year and was not correlated with monthly minimum temperatures. Therefore, the observed aggregations could not be exclusively related to the gain of a thermoregulatory advantage. All-male and all-female aggregations were more frequent during the mating season, following which some females seemed to engage in communal nesting and continued to share nests with some of their offspring well beyond the weaning period. Our data suggest that nest sharing was only partly affected by basic reproductive needs. We hypothesize that dormouse aggregations were ultimately favoured by a high level of intra-sexual tolerance elicited by the presence of numerous kin-related and familiar individuals in the population. This seems to stem from the high inter-individual spatial overlaps and the promiscuous mating system previously reported in this species. Further studies focusing on natural resting sites and genetic relatedness between individuals are needed to confirm our findings and test our hypothesis.

Seasonal and Sexual Variation in Metabolism, Thermoregulation, and Hormones in the Big Brown Bat (Eptesicus fuscus).

In response to seasonal variation in energy availability and thermal environment, physiological and endocrine mechanisms have evolved in temperate zone animals. Seasonal changes in hormone activity affect metabolism, body temperature, and reproductive activity. We examined the seasonal regulatory role of hormones on basal metabolic rate (BMR) and regulatory nonshivering thermogenesis (RNST) in 98 female and 17 male adult Eptesicus fuscus (big brown bat). We measured BMR, RNST, and plasma levels of thyroid hormone (T3), leptin, and cortisol in bats captured in maternity colonies in eastern Massachusetts from May to August (from arousal from the hibernation phase to the prehibernation phase). We hypothesized that all three hormones are seasonally primarily metabolic hormones and secondarily thermogenic hormones. In males, only BMR significantly changed seasonally. In females, all five variables significantly changed seasonally. The seasonal pattern of plasma leptin and cortisol levels correlated with the seasonal pattern of BMR, with an initial increase followed by a decrease, suggesting that leptin and cortisol are primarily metabolic hormones. The seasonal pattern of plasma T3 levels generally paralleled the basic seasonal pattern of RNST, with both increasing at the second half of the season, suggesting that T3 is primarily a thermogenic hormone. The observed decrease in plasma leptin levels may be necessary to allow for the observed seasonal decrease in BMR, with the similar cortisol pattern important for leptin regulation. While T3 is needed to maintain BMR, it may play a more critical role in the seasonal regulation of RNST than of BMR.