Showing papers in "Physiological and Biochemical Zoology in 1990"
TL;DR: Intestinal sucrase and maltase activities were measured in three species of hummingbirds and 11 species of passerine birds from western Mexico and found that Hummingbirds and passerines differed in the relationship between maltase and suCrase activities.
Abstract: Intestinal sucrase and maltase activities were measured in three species of hummingbirds and 11 species of passerine birds from western Mexico. Maximal sucrase activity standardized by nominal area of intestine was 2-118 times higher in hummingbirds than in the nine species of passerines that showed significant sucrase activity. Two species of passerines (Turdus rufopalliatus and Catharus aurantiirostris) lacked significant sucrase activity. Lack of functional sucrase activity has been reported in five species of passerine birds restricted to three closely related families (Muscicapidae, Sturnidae, and Mimidae). Interspecific variation in sucrase activity is probably influenced both by feeding habits and phylogenetic affinities. No allometric relation between sucrose hydrolysis capacity and body mass was found. When the two species with no significant sucrase activity were deleted from the sample, maltose hydrolytic capacity and body mass were allometrically related (exponent = 0.65). Maltase and sucrase ...
199 citations
TL;DR: Average performance varied significantly among years, but stamina varied more than did speed, and individual speed and stamina are both significantly repeatable over at least 1 yr.
Abstract: We examined correlates (sex, size, age) of variation in maximal burst speed (racetrack) and in stamina (time until exhaustion at 0.5 km · h⁻¹) in two populations of the iguanid lizard Sceloporus merriami in Big Bend National Park, Texas. Because these populations were known demographically and were studied in several years, we were able to examine the effects of adult age on performance, the between-year repeatability of individual performance, and environmental correlates of yearly variation in performance. Variation in locomotor capacities was striking. Males were faster than females, and lizards from the Grapevine Hills were faster than those from Boquillas (lower elevation). However, sex and population did not affect stamina. Young adults (1-yr-olds) were slightly faster but had slightly less stamina than did older adults (2-3-yr-olds). Adult size (mass, snout-vent length, hind limb length) had little effect on performance. Average performance varied significantly among years, but stamina varied more ...
183 citations
TL;DR: Data suggest significant metabolic cold adaptation of aerobic energy metabolism reliant upon fatty fuels in polar species, but a lack of such adaptation in pathways of carbohydrate metabolism in Temperate Zone fishes.
Abstract: Biochemical indices of metabolic cold adaptation were studied in muscular tissues of ecotypically similar Antarctic and Temperate Zone marine fishes. Pairwise comparisons were made between sluggish bottom-dwelling (polar: Notothenia gibberifrons; temperate: Myoxocephalus octodecimspinosus) and more active pelagic (polar: Trematomus newnesi; temperate: Tautoga onitis) species to ensure that results reflect differences in thermal habitats rather than life histories. Maximal activities of enzymes from central pathways of aerobic energy metabolism (citrate synthase, cytochrome oxidase) were 1.5-5-fold higher in oxidative muscles from polar species than from Temperate Zone counterparts when assayed at 1° C. Under similar conditions, enzyme markers for fatty acid oxidation (carnitine palmitoyltransferase, 3-hydroxyacyl-CoA dehydrogenase) were 1.3-27-fold higher in tissues from polar species, while those for both aerobic (hexokinase) and anaerobic (6-phosphofructokinase, pyruvate kinase, and lactate dehydrogenas...
182 citations
TL;DR: It appears that the anatomy and physiology of fruit eaters result in less than complete digestion and absorption of sugars, which may lie in the ability of frugivores to process large amounts of fruitper unit time in spite of the constraint gut volume might place on fruit intake.
Abstract: Researchers have historically assumed that short food retention time is a typical trait of frugivorous birds, and our data support this. Because absorptive efficiency is directly related to retention time and absorption rate, we predicted that either rates of nutrient absorption would be higher in frugivores than other birds to compensate for short retention or that absorptive efficiencies would be lower. In the fourpasserine species that we studied, the more frugivorous species had higher intestinal glucose (but notproline) transport activity than the more insectivorous and carnivorous species and higher intestinal sucrase activity. But compared with those of chickens and hummingbirds, small intestines of frugivorous passerines (four species) did not have high rates of glucose and proline uptake in vitro. In accordance with our prediction, in vivo digestive efciency of radiolabeled glucose was 92% in frugivorous cedar waxwings (88% for fructose) and 73% in fruit-eating American robins, less than the expe...
140 citations
TL;DR: Seasonal changes in standard metabolic rates seemed to be influenced by changes in reproductive condition as well as ambient temperature.
Abstract: We used a swimming respirometer to measure oxygen consumption (i. e., metabolic cost) of four species of stream fishes while they held position at diferent velocities. We tested naturally acclimatized individuals during spring, summer, fall, and winter at seasonal temperatures and photoperiods. Rosyside dace (Clinostomus funduloides), longnose dace (Rhinichthys cataractae), mottled sculpin (Cottus bairdi), and juvenile rainbow trout (Oncorhynchus mykiss) all showed seasonal changes in oxygen consumption. Seasonal changes in standard metabolic rates seemed to be influenced by changes in reproductive condition as well as ambient temperature. The metabolic cost of maintaining position for rainbow trout and rosyside dace generally increased with velocity. At velocities below eight body lengths per second, longnose dace did not exhibit a significant change in oxygen consumption, because they held position without swimming. At higher velocities, however, long-nose dace swam to maintain their position and oxygen...
134 citations
TL;DR: Large particles were digested at significantly lower rates, and time to initiation of cell wall degradation by microbes was signifcantly longer for large particles, which have important implications for digestive processing in herbivores, such as reptiles, that only minimally reduce food particle size.
Abstract: We examined the effect of reduction in food particle size on the rate and extent of fermentation of dry matter and cell walls in ruminants using in vitro and in sacco techniques. Large particles were digested at significantly lower rates, and time to initiation of cell wall degradation by microbes was signifcantly longer for large particles. Even after 144 h, large particles were digested to a lesser extent than were small particles. These results have important implications for digestive processing in herbivores, such as reptiles, that only minimally reduce food particle size. In these herbivores, digesta must be retained for much longer periods of time to achieve digestive efficiencies similar to those of herbivores that reduce food particle size to a greater extent. Length of retention time is a function of the amount of surface area exposed to microbial attack, not total surface area. Microbial activity concentrates in areas not protected by the cuticle. Because of the complexity of plant structure, r...
122 citations
TL;DR: Although open circulatory systems differ greatly in anatomy from closed blood systems, they are, nonetheless, functionally equivalent.
Abstract: Open circulatory systems have been portrayed aspoorly designed systems with poor performance characteristics, lacking in adequate tissue perfusion or fine control mechanisms. Recent studies cast doubt on these assumptions. Open circulatory systems of at least the higher Malacostraca have elaborate capillary beds in many tissues. Cardiac outputs are generally higher than those of the closed systems of poikilothermic vertebrates of equivalent size and activity potential. Although arterial pressures and flows are often lower than those characteristic of poikilothermic vertebrates, the crustacean arterial system is adapted to deliver equivalent flows under these conditions. The control systems of the crustacean neurogenic heart appear capable offine graded control over cardiac output. In addition, although crustaceans lack the arteriolar smooth muscle upon which much of theperipheral circulatory control of vertebrate closed systems depends, cardioarterial valvular mechanisms under neural and neurohormonal con...
117 citations
TL;DR: It is concluded that a single meal initiated a surge of protein synthesis in the tissues of Carcinus that was closely correlated with total oxygen consumption and that occurred initially through an increase in RNA activity.
Abstract: The oxygen consumption of the crab Carcinus fed a single meal of Mytilus tissue equivalent to 2.6% of the crabs' fresh weight increased 2.3-fold at 3 h after the meal and returned to its previous value within 24 h. The whole-body protein synthesis rates of animals fed meals of similar size paralleled the oxygen consumption changes; protein synthesis rates increased twofold by 3 h after the meal and remained elevated for 16h. Estimates of the minimal costs of protein synthesis indicated that they accounted for between 20% and 37% of the measured oxygen consumption. There was a linear correlation between protein synthesis rates and oxygen consumption rates. The protein synthesis rates of the midgut gland, gill, heart, proventriculus, leg extensor muscle, and claw muscle all increased by 3 h after a meal, but only in the claw muscle was this stimulation in protein synthesis prolonged. These initial increases in protein synthesis were not accompanied by any significant change in RNA:protein ratios in any of t...
113 citations
TL;DR: The South American field mouse Abrothrix andinus (Rodentia: Cricetidae) is a small mammal active throughout the year in the Andes, despite substantial seasonal environmental changes, and body mass exhibited a significant decrease during winter, and maximum metabolic rate for thermoregulation increased during winter.
Abstract: The South American field mouse Abrothrix andinus (Rodentia: Cricetidae) is a small mammal active throughout the year in the Andes, despite substantial seasonal environmental changes. Body mass exhibited a significant decrease during winter, and maximum metabolic rate for thermoregulation increased by 36.6%. In absolute terms, the maximum thermal differential between body and environmental temperatures increased 44° C during winter. On the other hand, body temperature and thermal conductance did not show significant changes through the year; however, mass-independent conductance decreased in winter. Parallel to these changes, the length and dry mass of the total digestive tract changed significantly with wintertime; at the same time the length and mass of the small intestine and the length of the large intestine also showed significance. Significant differences in gastrointestinal morphology between males andfemales were found only during the reproductive season (summer).
103 citations
TL;DR: Investigating factors that affect heat loss in small Cetacea and to compare these factors in harbor porpoises and spotted dolphins implies that small cetaceans can use a combination of surface area and insulative quality and quantity to thermoregulate.
Abstract: Harborporpoises (Phocoena phocoena) and spotted dolphins (Stenella attenuata) must cope with very different thermal situations. Harbor porpoises live in cold coastal waters where water temperatures average 10° - 15° C; spotted dolphins live in the Eastern Tropical Pacific Ocean ecosystem where water temperatures average 27° C. There are few options available to cetaceans for thermoregulation. Thepurpose of the present study was to investigate factors that affect heat loss in small Cetacea and to compare these factors in harbor porpoises and spotted dolphins. Phocoena had a smaller surface area, for a given mass, than did Stenella. This suggests possible selection for a decreased surface area/body mass ratio in harbor porpoises. Conductivity of harbor porpoise blubber (0.10 ± 0.01 W m⁻¹ °C⁻¹, n = 29) was significantly lower (P < 0.05) than that of spotted dolphins (0.20±0.02 W m⁻¹ °C⁻¹, n = 16), signifying a higher insulative quality for Phocoena. In addition to being a superior insulator, Phocoena blubber...
99 citations
TL;DR: The hypothesis that proportional substitution of exercise thermogenesis partially accommodates thermoregulatory requirements of small, free-ranging birds is supported.
Abstract: To test the hypothesis that heat produced as a by-product of physical activity substitutes for avian thermoregulatory requirements, we measured daytime CO₂ production of a very active small passerine, the verdin (Auriparus flaviceps), at various standard operative temperatures ($T_{es}$). We used the doubly labeled water method to measure active period field metabolic rates ($FMR_{a}$) of verdins in their natural habitat, and compared our results to laboratory measurements of daytime resting metabolism ($RMR_{a}$) and time-budget (TB) estimates of $FMR_{a}$. Active-period metabolic expenditures decreased with increasing $T_{es}$, but the temperature dependence of $FMR_{a}$ difered from that of $FMR_{a}$ such that in the cold the two functions converged. TB estimates of $FMR_{a}$ (computed by a model assuming activity costs were additive) were higher than measured $FMR_{a}$ at low $T_{es}$. These results support the hypothesis that proportional substitution of exercise thermogenesis partially accommodates ...
TL;DR: Regression analyses suggest that minimum Tb and minimum Ta are more strongly correlated with torpor bout duration than V̇o2 in both species.
Abstract: Torpor bouts of mammalian hibernators are generally shorter at the beginning and end and are consistently longer during the main part of the hibernation season. Because it is not known why the duration of torpor bouts changes at the beginning and end of the hibernation season, we studied thisphenomenon in two sciurid rodents: Spermophilus saturatus (200-300g) and Eutamias amoenus (45-60g). We examined the seasonal change in torpor bout duration during hibernation at a constant air temperature (Ta) of20 C in relation to (1) the minimum body temperature (minimum Tb) to which the animals could be experimentally cooled before they maintained a constant Tb or began to arouse, (2) Ta at the time of minimum Tb (minimum Ta), and (3) oxygen consumption (Vo2) of torpid individuals atTa 2" C. Average duration of torpor bouts during the main part of the hibernation season was about 11 d in S. saturatus and 8-9 d in E. amoenus; in response to experimental cooling, minimum Tb of both species declined as low as-0. 2 C. In early and late hibernation, when torpor bouts were short, minimum Tb, minimum T,, and Vo, during torpor were higher than in the main part of the hibernation season. Regression analyses suggest that minimum Tb and minimum Ta are more strongly correlated with torpor bout duration than Vo2 in both species.
TL;DR: Myocardial oxygen consumption increased linearly as a function of myocardial power output at both acclimation temperatures, and the slope of the regression equation was significantly lower at 5° C compared with that at 15° C.
Abstract: Oxygen consumption and maximum pumping performance were measured in situ perfused trout (Salmo gairdneri) hearts at acclimation temperatures of 5° and 15° C. Myocardial oxygen consumption increased linearly as a function of myocardial power output at both acclimation temperatures. The slope of the regression equation was significantly lower at 5° C compared with that at 15° C This difference was attributed to power output related changes in mechanical efficiency at 5° C (but not at 15° C) and a lower mass-specfic oxygen consumption for maximal performance of the larger heart of cold-acclimated fish.
TL;DR: The hummingbird is a unique animal: its kidney appears to be structurally similar to that of a reptile, but its rate of waterflux is more typical of an amphibian; it sustains a metabolic level as high as that of any endotherm.
Abstract: Hummingbirds subsist almost entirely on a liquid diet composed of floral nectar, and, when energy demands are high, they can consume more than three times their body mass in fluid per day. At the same time, however, the hummingbird's high metabolism requires efficient extraction of energy and nutrients from a dilute food source that is passing rapidly through the gastrointestinal (GI) tract. The ability of the hummingbird to efficiently process and excrete such large volumes of water must surely entail structural or functional specializations of the kidney and GI tract. The rate of waterflux and nutrient extraction efficiency are also influenced, however, by the animal's feeding behavior. Because meal size affects the passage rate of food through the digestive tract (and, therefore, assimilation efficiency), feeding frequency and the amount of nectar consumed per feeding bout will affect the efficiency of nutrient absorption. Ultimately, the water and nutrient content of the nectar produced by the plants ...
TL;DR: Calculations show that, at Ta's likely to be encountered at night in nature, rufous hummingbirds can save energy by entering torpor even if they arouse immediately without an intervening period ofsteady-state torpor.
Abstract: Continuous records of nighttime O₂ consumption ($\dot{V}o_{2}$)from rufous hummingbirds (Selasphorus rufus) were used to determine O₂ consumption during normothermic nighttime rest, entry into torpor, steady-state torpor, and arousal from torpor over a range of air temperatures ($T_{a}$)from - 1° to 24° C. Whereas entry into torpor occurred anytime during the first 9.5 h of the 12-h night, arousals were consistently initiated within 2.5 h of the end of the night in the absence of known environmental cues. During normothermic rest, $\dot{V}o_{2}$ was inversely related to $T_{a}$ over the entire temperature range. During steady-state torpor, $\dot{V}o_{2}$ reached its lowest value at a $T_{a}$ of approximately 8° C (= $T_{a\dot{V}o_{2}min}$). The measured minimum body temperature ($T_{bmin}$) was approximately 13° C The comparatively low values of $T_{bmin}$ and $T_{a\dot{V}o_{2}min}$ for this temperate-zone migrant species may represent an adaptation for surviving low nighttime $T_{a}'s$ in nature. Duratio...
TL;DR: The results suggest that cardiovascular and ventilatory reflex responses to hypoxia in channel catfish are mediated by both externally and internally oriented O₂-sensitive chemoreceptors.
Abstract: Sodium cyanide (NaCN) was used as a chemical probe to help localize externally and internally oriented oxygen-Sensitive chemoreceptors and to identify the reflex effects they control in anesthetized, spontaneously breathing channel catfish (Ictalurus punctatus). Fish responded rapidly to NaCN (500μg) given in the inspired water flow (external NaCN) with transient bradycardia and a more prolonged stimulation ofgill ventilation frequency ($f_{g}$) and opercularpressure amplitude ($P_{OP}$). Internal injections of NaCN (50 μg), given via the dorsal aorta, stimulated $f_{g}$ and $P_{OP}$ after about a 42-s latency but had no effect on heart rate ($f_{b}$). Injections of NaCN (50 μg) into the ventral aorta significantly reduced the latency of response, stimulating $P_{OP}$ and $f_{g}$ in 9-16s. Cardiovascular and ventilatory variables returned topreinjection levels within 30 min. These results suggest that cardiovascular and ventilatory reflex responses to hypoxia in channel catfish are mediated by both extern...
TL;DR: A multiregression equation is presented to describe the interacting effects of body mass and temperature (T) on specific metabolic rate: M′ = cTBW(b′+rlnT), where r is a new coeficient describing the interaction effect, and c is a proportionality constant for temperature.
Abstract: Resting metabolic rates of young southern catfish (Silurus meridionalis Chen) weighing 10. 8-422.6 g were measured by use ofa continuous-flow respirometer. Mean specific metabolic rates at 10°, 15°, 20°, 25°, and 30° C were 21.48, 40.47, 56. 81, 92.79, and 115.48 mg O₂/kg/h, respectively. Values of the mass exponent (b) in the relationship between metabolic rate (M) and body mass (W) ($M = aW^{b}$, where a is a proportionality constant) decreased with increasing temperature from 0.9401 at 10° C to 0.7476 at 30° C Values of the temperature exponent (B) in the relationship between mass-specific metabolic rate (M′) and temperature ($M\prime = AW^{B}$, where A is a constant specific to the species) decreased with increasing body weight, from 1. 7196 for fish weighing 36.14 g to 1.2507 for fish weighing 291.99 g. Thispaperpresents a multiregression equation to describe the interacting effects of body mass and temperature (T) on specific metabolic rate: $M\prime = cT^{B}W^{(b\prime+rlnT)}$, where r is a new coe...
TL;DR: The elevated metabolism of females during pregnancy is greater than can be accounted for by the increased mass of the pregnant female, indicating that the mass-specific oxygen consumption of the embryos is not scaling to maternal body mass.
Abstract: Metabolic rates of gravid females of the viviparous lizard Sceloporus jarrovi are higher than those of nonreproductive lizards: the allometric relationship between oxygen consumption and body mass in gravid females ($\dot{V}O_{2} = 0.437m^{.735}$) has a statistically equivalent slope but a significantly higher intercept than that for males ($\dot{V}O_{2} = 0.225 m^{.812}$). The elevated metabolism of females during pregnancy is greater than can be accounted for by the increased mass of the pregnant female, indicating that the mass-specific oxygen consumption of the embryos is not scaling to maternal body mass. In fact, metabolism of gravid females is even higher than predicted if embryo metabolism is scaling to embryo body mass. Mean oxygen consumption of newborn S. jarrovi (mean body mass = 0.75 g) was 0.245 cm³ O₂ • h⁻¹, which is 1.4 times higher than that predicted from the allometric relationship for nonpregnant adults, but it is not statistically different from estimates of metabolism of embryos just...
TL;DR: This analysis assesses the influence of two covariates, ovum size and temperature, on the three parameters above for two orders of amphibians, anurans and caudates, and provides a basis for evaluating the influenceof reproductive mode on parameters of embryonic development.
Abstract: Incubation time in amphibians can be mathematically partitioned into two other parameters as follows: Incubation time = rate of embryonic development⁻¹ X protraction of development. The latter parameter is important because it reflects the degree of development of the embryo at hatching. Protraction of development is defined as the ratio of incubation time to time taken to reach a neurula stage common to all amphibians, and it is directly correlated with Gosner stage at hatching in anurans (n = 30 species). This analysis assesses the influence of two covariates, ovum size and temperature, on the three parameters above for two orders of amphibians, anurans and caudates. The ANCOVA of 55 species in 17 families shows that incubation time scales to ovum $volume^{0.444} . e^{-0.121temp}$ (multiple R² = 0. 88), rate ofdevelopment scales to ovum $volume^{0.435} . e^{0.115temp}$ (multiple R² = 0.90), and protraction of development is not significantly related to either ovum volume or temperature. Ovum volume is i...
TL;DR: The cutaneous resistances to water vapor flux of these Australian frogs were much higher than those usually associated with amphibians, averaging 9 and 39 s cm⁻¹ for L. caerulea and L. chloris, respectively.
Abstract: The rate of evaporative water loss (EWL) of the Australian tree frogs Litoria caerulea and Litoria chloris was evaluated over the temperature intervals 25°–50° C and 25°–47° C, respectively. At 25°...
TL;DR: Quantitative analysis of the composition of eggs and their sibling neonates in the viviparous natricine snake Thamnophis ordinoides revealed that yolk provided the principal source of organic nutrition but that embryos received a substantial allotment of inorganic nutrients from the placentas.
Abstract: Quantitative analysis of the composition of eggs and their sibling neonates in the viviparous natricine snake Thamnophis ordinoides revealed that yolk provided the principal source of organic nutrition but that embryos received a substantial allotment of inorganic nutrients from the placentas. The placental provision of water and sodium equaled or exceeded yolk supplies, and placental transport accounted for 23% of neonatal calcium composition. There was no difference between egg and newborn quantities of total phosphorus or total potassium, whereas neonates contained less total magnesium than eggs. The mode of embryonic nutrition in this species is characterized as predominantly lecithotrophic, yet placental nutrient provision contributes significantly to embryonic nourishment. Placental transport of sodium and embryonic uptake of water was greater in recently ovulated eggs that contained relatively low levels of sodium and water respectively. Thus, placental sources compensated for low yolk provision. P...
TL;DR: The results suggest that balanced metabolic function is retained during starvation in fishes, and that starvation may have differential effects on high- and low-speed swimming abilities.
Abstract: Starvation of the fish Paralabrax nebulifer was accompanied by complex changes in the synthesis rates of different classes of proteins within the white muscle. Synthesis of white-muscle myofibrillar proteins, as measured by incorporation of $^{14}C-leucine$, decreased rapidly during starvation, whereas synthesis of total sarcoplasmic proteins was unchanged. Although actin and aldolase label incorporation in white muscle underwent an immediate decrease to approximately 10% of control, lactate dehydrogenase and creatine phosphokinase showed a smaller initial decrease. Relative activities of white-muscle glycolytic enzymes were conserved despite a significant loss in overall glycolytic capacity. Control of specific synthesis rates may be important in maintaining an overall balance of proteins with different half-lives. In red muscle, starvation led to no reductions in the synthesis of any protein examined. Changes in muscle protein synthesis rates were reflected in a larger decrease in RNA/DNA ratio in white...
TL;DR: The experiments indicate that a physiological constraint acting on nestling ibis is responsible for the fact that ibis breeding in coastal colonies fly long distances inland to secure freshwater prey for their young.
Abstract: We monitored the growth and metabolism of 28 nestling white ibis (Eudocimus albus) taken at 21 d of age and hand-reared for 3 wk on ad lib. diets of (1) freshwater crayfish (Procambarus clarkii; salt content 535 mosm kg⁻¹; n = 12), (2) brackishwater fiddler crabs (Uca spp.; 1,080 mosm kg⁻¹; n = 12), and (3)freshwater crayfish salt-loaded to a salt content approximating that of fiddler crabs (1,090 mosm kg⁻¹; n = 4). Brackish water (480 mosm kg⁻¹) or fresh tap water was provided to the birds on an ad lib. basis. Nestlings maintained on the unaltered-crayfish diet gained mass at rates similar to those of parent-reared nestlings. Birds on the fiddler-crab and salt-loaded crayfish diets lost approximately 3% of their body massper day until fresh water was substituted for brackish water 7 d into the experiment. Nestling hematocrits, serum osmolality, and serum electrolyte levels indicated that during the first week of the experiment, nestlings on the two high-salt diets were dehydrated and salt loaded. This oc...
TL;DR: The Florida red-bellied turtle, Pseudemys nelsoni, on a diet of the aquatic plant Hydrilla verticillata, has high digestive efficiencies for dry matter, organic matter, energy, and cell walls, and moderate digestive efficiency for nitrogen, and the shift of fermentation into the small intestine demonstrates that, at least in P. n Nelsoni, digestive strategy is not constrained by gut morphology.
Abstract: The Florida red-bellied turtle, Pseudemys nelsoni, on a diet of the aquatic plant Hydrilla verticillata, has high digestive efficiencies for dry matter, organic matter, energy, and cell walls, and moderate digestive efficiency for nitrogen. High cell wall digestibilities are a result of microbial fermentation in both the small and large intestines. Digestibilities are higher than most values reported for herbivorous reptiles on foliage diets. Mass-specific intake falls within the range measured in freefeeding herbivorous reptiles. Fermentation in the small intestine has not been reported previously in reptiles. Endproducts of fermentation-volatile fatty acids (VFAs) and gases-and concentration and rate of production of VFAs are similar to those in other herbivores. Fermentation in the small intestine has important nutritional consequences, such as a competition between endogenous enzymes and gut microflora for the highly nutritious, soluble substrate in the digesta of the small intestine. Energy from VFAs...
TL;DR: Overnight force-feeding of chick starter mash or serial injection of cysteine attenuated overnight utilization of liver and muscle glutathione, indicating a specific role for GSH as a Cysteine reservoir.
Abstract: In molting birds keratin synthesis is intense and continuous through day and night. Keratins are much richer in cystine than are most tissue proteins. We hypothesized that glutathione (γ-glutamylcysteinylglycine) helps to sustain feather synthesis and spare bodyprotein during overnight fasting by serving as a cysteine reservoir. To test this hypothesis, we measured the responses of liver and muscle glutathione and protein pools to various feeding schedules (cysteine supply) andperiods of overnight fasting (cysteine demand) in molting white-crowned sparrows. Our main purpose was to ascertain whether these pools change passively or are instead regulated in relation to cysteine need in the postabsorptive state. During molt, significantly more liver glutathione and pectoralis protein were stored by day and utilized overnight than in postmolt. Liver glutathione and pectoralis protein were stored and utilized diurnally during molt in proportion to the duration of the overnight fast (12 h > 8 h > 4 h). Diurnal c...
TL;DR: The order of change in the measured parameters suggests that adjustments in the CO2 content of the body contribute to the induction and termination of daily torpor in deer mice.
Abstract: Retention of CO₂ and respiratory acidosis have previously been reported to accompany entrance to hibernation, with acid-base and CO₂ balance returning to normal upon arousal from hibernation. The present study indicates that these alterations are not limited to species which have the ability to undergo deep hibernation, but are also involved in another mammalian dormancy state, daily torpor. Deer mice (Peromyscus maniculatus) were used to examine the time course of changes in respiratory quotient (RQ), metabolic rate (MR), and body temperature ($T_{b}$) during daily torpor at an ambient temperature of 10° C For several hour sprior to daily torpor, RQ steadily declined from 0.92 to 0. 74, indicating a shift in primary metabolic substrate from carbohydrate to fat, while MR and $T_{b}$ remained constant at 4.23 ± 0 44 mL O₂/g • h and 36.6° ± 0.9° C, respectively. Entrance to daily torpor involved a transitory decrease in RQ (0.74-0 63-0.73) that lasted less than 12 min and reflected CO₂ retention and accompa...
TL;DR: Under most conditions, stressful Tes's did not appear to limit time needed for foraging, but thermal constraints may have been important for young that also faced declining food quality at the end of the growing season.
Abstract: This is the publisher's version, which can also be found at:http://www.jstor.org/stable/30158178
TL;DR: The results demonstrate the existence of population differences in the responses of deer mice to a predator and suggest that the population Differences in responses may be related to a differential activation and/or expression of BDZ and opioid-sensitive mechanisms.
Abstract: This article examines the neuromodulatory mechanisms associated with predator recognition and responses in a mainland and an island population of deer mice, Peromyscus maniculatus. In a weasel-sympatric mainland population of deer mice, P. m. artemisiae, a 30-s exposure to the presence (scent) of the short-tailed weasel (Mustela erminea) elicited immediate and relatively short-lasting increases in the latency of response to aversive stimuli. These enhanced nociceptive thresholds (analgesic responses) were mediated by benzodiazepine-sensitive mechanisms that have been associated with the mediation of fear and fright behaviors and antipredator defensive mechanisms. A 5-min exposure of the mainland animals to the weasel elicited an analgesic response that was both benzodiazepine (BDZ) and opioid sensitive, while 15-min exposures induced only the relatively prolonged opioid-mediated analgesic responses. Opioid activation and opioid-mediated behavioral responses are generally associated with exposure to stress...
TL;DR: The prehatch peak in metabolic rate may reflect a development mode evolved in reptiles nesting in highly variable environments, and provide a flexible hatching schedule that can be matched to environmental conditions without incurring major energetic costs.
Abstract: The metabolic rate of Crocodylus johnstoni eggs was measured through incubation at 29° and 31° C, and in C. porosus eggs at 30° C. The pattern of metabolic rate in both species ispeaked, similar to patterns recorded in other embryonic reptiles that develop in hard:shelled (cleidoic) eggs. Maximum $\dot{V}_{O_{2}}$ occurs when incubation is less than 90% complete. Total oxygen consumed ($V_{O_{2tot}}$) by C. johnstoni eggs is higher at 29° C (86.2 mL·g⁻¹ [STPD]) than at 31° C (77.8 mL· g⁻¹[STPD]). Yolk-free mass of 29° C hatchlings is, however, higher, so that mass-specific $V_{O_{2tot}}$ is similar at both temperatures. The prehatch peak in metabolic rate may reflect a development mode evolved in reptiles nesting in highly variable environments. An exponential pattern of growth early in incubation followed by a period of limited growth and declining energetic demands combine to provide a flexible hatching schedule that can be matched to environmental conditions without incurring major energetic costs.
TL;DR: It is suggested that leatherback turtles rely on their enhanced blood and tissue O₂ stores rather than the lung O⁂ store during deep dives, which is similar to that of most mammals.
Abstract: We have investigated aerobic metabolism and blood O₂ transport properties of the leatherback sea turtle (Dermochelys coriacea). During nesting, at a body temperature of 29° C, resting ventilation (9.2 ± 1. 7 mL min⁻¹ kg⁻¹) and O₂ consumption (0. 25 ± 0.04 mL min⁻¹ kg⁻¹; three turtles) were slightly below values given for other sea turtles. Tidal volume was considerably smaller than in other turtles (4.0 ± 1.06 mL kg⁻¹) suggesting that Dermochelys has small lungs. Blood (measured in four turtles) had an extremely high Hb concentration (15. 6 ± 1.8 g dL⁻¹), hematocrit (39% ± 1.2%), and carried 21 ± 2.5 mL · dL⁻¹ blood, which exceeds the blood O₂ carrying capacity of other sea turtles and was similar to that of most mammals. Pectoral muscle myoglobin content, indicative of tissue O₂ stores, was 4.9 g dL⁻¹, twice that of other sea turtles. The $P_{50}$, however, was similar to that of the loggerhead sea turtle: 31 and 40 mmHg for blood equilibrated with 2.2% (pH 7. 84) and 5% (pH 7.52) CO₂, respectively. We s...