Heating and cooling rates of eastern diamondback rattlesnakes,Crotalus adamanteus

• 1.Establishing if and how organisms modulate temperature changes is an important component of understanding their thermal biology.
• 2.We used temperature-sensitive radio-transmitters to monitor heating and cooling rates between 5 and 35 °C of four Crotalus adamanteus in the laboratory.
• 3.We found no difference between heating and cooling rates in C. adamanteus. Additionally, rates of temperature change mirrored those of a biophysical model, further suggesting a lack of physiological thermoregulation.
• 4.Our findings contrast previously published studies that demonstrate active temperature control of similarly sized reptiles and demonstrate a need for more investigations of physiological thermoregulation in reptiles.

     

Ecological strategies and fitness tradeoffs inEscherichia coli mutants adapted to prolonged starvation

Many bacteria in nature are nutritionally deprived, and there has been heightened interest during the past decade in the properties of these bacteria. We subjected five populations ofEscherichia coli to prolonged starvation in a minimal salts medium, during which time the density of viable cells declined by several orders of magnitude. From each one, we isolated a surviving clone that showed some heritable difference in colony morphology. We then characterized these mutants in two ecologically relevant respects. First, we determined the nature of their selective advantage, if any, during prolonged starvation. (i) Three of the five mutants had significantly lower net death rate when progenitor and mutant clones were starved separately. (ii) Three mutants showed a significant reduction in death rate in mixed culture that was frequency dependent and manifest when the mutant clone was initially rare. This pattern suggests that these mutants fed on some byproduct of progenitor cells (living or dead). (iii) Two mutants caused the death rate of their progenitors to increase significantly relative to the rate measured in the absence of the mutant. This pattern suggests that these mutants had become allelopathic to their progenitors. Thus, three distinct ecological adaptations to prolonged starvation are evident. No advantage was detected for one mutant, whereas two mutants exhibited multiple advantages. Second, we asked whether the starvation-selected mutants were as fit in growth-supporting conditions as their progenitors. All five mutants were inferior to their progenitor during competition in fresh medium. Evidently, there is an evolutionary tradeoff between performance under growth and starvation conditions.     

Coexisting small mammals display contrasting strategies for tolerating instability in arable habitat

Small mammal species are abundant and common throughout Europe and often utilise areas that are subject to agricultural land use. Arable farmland is an example of a frequently disturbed habitat, and this study questioned how such disturbance affected the two most common species in the region; one a habitat generalist and one a habitat specialist. We confirmed the prediction that wood mice (Apodemus sylvaticus, a habitat generalist) would make use of a variety of habitats and that bank voles (Myodes glareolus, a habitat specialist) would make greater use of the more stable portions of the study site. We surveyed the study site intensively in order to test whether there was continuity in the spatial arrangement of individuals of both species, given the strategy employed. The spatial arrangement of wood mice varied with season but remained stable for bank voles. We found no association, positive or negative, between the spatial distributions of the two species, suggesting that spatial competitive exclusion did not occur. This work provides further insight into how these small mammal species are affected by agricultural disturbance and predictions can be made about how the species will respond under CAP Reform greening practices.     

Some physiological and biochemical features of starvation and refeeding in small wild rodents (Microtinae)

Blood glucose and leucocytes and liver glycogen and lipids were investigated in Cl. rutilus and Cl. rufocanus fasted for 0, 6, 12, 18 and 22 hr. It was observed: 1. In both species blood glucose content drops (1.3-1.5 times) by 6 hr, slowly rises by 12 hr and then progressively and strongly declines up to the end of starvation (36% and 27% of control for Cl. rutilus and Cl. rufocanus respectively). 2. Liver glycogen was depleted by 6 hr of fasting while lipids accumulate in liver during starvation in a large quantity (3.4-3.6 times at the end). 3. White blood cells content in fasted animals decreases. At one end of starvation it equals 23% and 16% of control for Cl. rutilus and Cl. rufocanus, respectively. 4. Hypoglycemia in Microtinae during starvation is pronounced compared with that in Muridae. Leucopenia and accumulation of lot of lipids in liver are new phenomena for fasting. 5. After refeeding hyperglycemia develops, the liver accumulates large quantities of glycogen. Recovery of all indexes slow. Complete normalization does not occur by 16 hr of refeeding.     

Response of two species of clams, Ruditapes decussatus and Venerupis pullastra, to starvation: physiological and biochemical parameters

Adult specimens of two species of clams, Ruditapes decussatus and Venerupis pullastra, were starved for 84 days to determine the effect of starvation on their metabolism. The energy cost of metabolism in starvation was assessed using the oxygen consumption rates (respiration rates) of the clams and assessing the type of fuel used to provide this energy by analyzing their biochemical composition. Respiration rates decreased in both species after 15 days of starvation and remained at basal levels throughout the rest of the experimental period. Both during the first period and also after the metabolism had slowed down, the amount of energy consumed in respiration was higher in V. pullastra than in R. decussatus. The energy needed to maintain vital functions in both species is obtained from catabolism of body components, with a reduction in dry mass of the specimens, and consequently their energy content, in both species. This reduction was greater in V. pullastra given that energy demand is higher in this species. In both species carbohydrates made the largest contributions to energy output, followed by lipids in males and proteins in females. However, the energy contribution of each biochemical component differs according to species: R. decussatus obtains its energy from the catabolism of carbohydrates and proteins in equal proportion, while V. pullastra obtains it from proteins and lipids. In both species, albeit to a greater extent in R. decussatus, we observed that female specimens conserved their lipids until the later stages of the period of starvation (day 70), after which they started to metabolise their lipid components more intensely. The interspecific differences are interpreted in relation to the different habitat occupied by the two species.     

The cell in starvation; physiological and chemical observations

Observations made on Amoeba proteus during total inanition revealed the following changes: Dry weight declined progressively, but at a decreasing rate to about 45 per cent of the initial levels when determined in surviving members of a dying population. Protein fell to about 70 per cent of the initial level. A hexane-alcohol extractable component fell during early starvation then rose to about its initial absolute level in the dying cells. While initially most of this component is probably lipide, it is not certain that other materials are not extracted during cell degeneration. Survival as a function of cell size was studied. No advantage in survival was apparent for any size class. Nucleate cell "halves" likewise showed no survival time differential, unlike a highly significant decrease in the survival of enucleate portions. The maintenance of the initial variance about the mean population weight (after hexane-alcohol extraction) during starvation, likewise supports the idea that survival depends largely on concentration parameters.     

Divider size and the cell cycle after prolonged starvation ofTetrahymena corlissi

Cell growth and division of the ciliateTetrahymena corlissi were examined upon refeeding after prolonged starvation of up to 12 days. Division did not automatically occur when a certain critical cell size was reached. Rather, it varied both with the nutritional history of the cell and the nutrient conditions in which the cell was growing. Upon refeeding, cells starved for 12 days divided at a smaller size and later than cells starved for 6 days. Cells refed at high density took longer to begin division than cells refed at low density. The results are discussed with respect to the relative starvation and critical constituent models of the cell cycle and in terms of the polymorphic life cycle ofTetrahymena species.     

Improved biochemical strategies for targeted delivery of taxoids

Paclitaxel (Taxol) and docetaxel (Taxotere) are very important anti-tumor drugs in clinical use for cancer. However, their clinical utility is limited due to systemic toxicity, low solubility and inactivity against drug resistant tumors. To improve chemotherapeutic levels of these drugs, it would be highly desirable to design strategies which bypass the above limitations. In this respect various prodrug and drug targeting strategies have been envisioned either to improve oral bioavailability or tumor specific delivery of taxoids. Abnormal properties of cancer cells with respect to normal cells have guided in designing of these protocols. This review article records the designed biochemical strategies and their biological efficacies as potential taxoid chemotherapeutics.     

Protein fragment complementation strategies for biochemical network mapping

The organization of biochemical networks that make up the living cell can be defined by studying the dynamics of protein-protein interactions. To this end, experimental strategies based on protein fragment complementation assays (PCAs) have been used to map biochemical networks and to identify novel components of these networks. Pharmacological perturbations of the interactions can be observed, and the resulting pharmacological profiles and subcellular locations of interactions allow each gene product to be 'placed' at its relevant point in a network. Network mapping by PCA could be used with, or instead of, traditional target-based drug discovery strategies to increase the quantity and quality of information about the actions of small molecules on living cells and the intricate networks that make up their chemical machinery.     

Behavioral and physiological responses of susceptible and resistant diamondback moth larvae to Bacillus thuringiensis

To determine whether field-selected resistance of diamondback moth (Plutella xylostella L.) (Lepidoptera: Plutellidae) to Bacillus thuringiensis is based on behavioral or physiological adaptation, we measured mortality, consumption, and movement of larvae from a susceptible and a resistant colony when placed on untreated and B. thuringiensis treated cabbage. Colonies did not differ in mortality, consumption, or movement on untreated cabbage. However, for a given amount of consumption of treated cabbage, resistant larvae had lower mortality than susceptible larvae, demonstrating that resistance had a physiological basis. The movement patterns could not account for the differences between colonies in survival. Resistant larvae did not avoid B. thuringiensis more than did susceptible larvae. Thus, we found no evidence for behavioral resistance.     

Oxidative stress and antioxidant defenses after prolonged starvation in Dentex dentex liver

The aim of this work was to evaluate the effects of prolonged starvation and refeeding on antioxidant status and some metabolic-related parameters in common dentex (Dentex dentex) liver. Fish deprived of food for 5 weeks showed a significant increase in lipid peroxidation, measured as malondialdehyde (MDA) levels. The activity of the antioxidative enzymes superoxide dismutase (SOD), catalase, and glutathione peroxidase (GPX) in starved fish significantly increased (by 42%, 22%, and 52%, respectively), whereas glutathione reductase (GR) activity was significantly depressed by 53% compared to controls. No qualitative changes in the SOD isoenzymatic pattern were detected by nondenaturing PAGE analysis, but the isoforms corresponding to CuZn-SOD I and II were enhanced in starved fish. The activity of the enzymes indicative of oxidative metabolism, beta-hydroxyacyl CoA dehydrogenase (HOAD) and citrate synthase (CS), significantly increased (by 123% and 28%, respectively), and that of glucose-6-phosphate dehydrogenase (G6PDH) was inhibited by 56%. Oxidative damage under these circumstances is reversible since all biomarkers assayed returned to control values after refeeding. Our results show that prolonged starvation leads to a pro-oxidant situation and oxidative stress despite activation of antioxidant defense mechanisms, and that inhibition of G6PDH activity might be responsible for this failure in cellular antioxidant defenses.     

Snakes survive starvation by employing supply- and demand-side economic strategies

Animals vary widely in their abilities to tolerate extended periods of food limitation. Although some snakes are known for their unique ability to survive periods of inanition that last up to 2 years, very little is known about the biological mechanisms that allow them to do this. Consequently, the present study examined physiological, compositional, and morphological responses to 168 days of starvation among three distantly related snake species (i.e., ball python, Python regius; ratsnake, Elaphe obsoleta; and western diamondback rattlesnake, Crotalus atrox). Results revealed that each of these species was able to successfully tolerate starvation by adaptively utilizing supply- and demand-side regulatory strategies. Effective demand-side strategies included the ability of snakes to depress their resting metabolic demands by up to 72%. Moreover, supply-side regulation of resources was evidenced by the ability of snakes to spare their structurally critical protein stores at the expense of lipid catabolism. Such physiological strategies for minimizing endogenous mass and energy flux during periods of resource limitation might help explain the evolutionary persistence of snakes over the past 100 million years, as well as the repeated radiation of snake lineages into relatively low-energy environments. The final section of this study outlines a novel modeling approach developed to characterize material and chemical flux through animals during complete inanition. This approach was used to make comparisons about the efficacy of various supply- and demand-side starvation strategies among the three species examined, but could also be used to make similar comparisons among other types of animals.     

饥饿和再喂食对泥鳅生化组成的影响

研究了泥鳅(Misgurnus anguillicaudatus)在18±0.5℃下,饥饿20 d和恢复喂食8 d的生化组成变化。结果表明,在饥饿初期,泥鳅鱼体的脂肪和蛋白质含量均明显地下降,饥饿15 d后,脂肪的降低量减少并趋于稳定,而蛋白质的含量则进一步显著降低。这表明在饥饿过程中,泥鳅首先动用机体的脂肪和蛋白质提供能源,饥饿至一定程度后则主要利用蛋白质。恢复喂食后这两种物质的含量均迅速回升,其中恢复喂食5 d后,脂肪和蛋白质的含量均达到初始水平。水分和灰分在饥饿过程中呈上升趋势,恢复后便开始下降;饥饿20 d后,鱼体的饱和脂肪酸含量基本保持不变,而多不饱和脂肪酸和单不饱和脂肪酸含量分别有一定的增加和降低,另外n-3系列脂肪酸含量升高,而n-6系列脂肪酸几乎不变。     

The metabolic effects of prolonged starvation and refeeding in sturgeon and rainbow trout

The present study examines the particular metabolic strategies of the sturgeon Acipenser naccarii in facing a period of prolonged starvation (72 days) and subsequent refeeding (60 days) compared to the trout Oncorhynchus mykiss response under similar conditions. Plasma metabolites, endogenous reserves, and the activity of intermediate enzymes in liver and white muscle were evaluated. This study shows the mobilization of tissue reserves during a starvation period in both species with an associated enzymatic response. The sturgeon displayed an early increase in hepatic glycolysis during starvation. The trout preferentially used lactate for gluconeogenesis in liver and white muscle. The sturgeon had higher lipid-degradation capacity and greater synthesis of hepatic ketone bodies than the trout, although this latter species also showed strong synthesis of ketone bodies during starvation. During refeeding, the metabolic activity present before starvation was recovered in both fish, with a reestablishment of tissue reserves, plasmatic parameters (glucemia and cholesterol), and enzymatic activities in the liver and muscle. A compensatory effect in enzymes regarding lipids, ketone bodies, and oxidative metabolism was displayed in the liver of both species. There are metabolic differences between sturgeon and trout that support the contention that the sturgeon has common characteristics with elasmobranchs and teleosts.