Weight-specific Basis Research Articles

Skeletal muscle protein accretion rates and hindlimb growth are reduced in late gestation intrauterine growth-restricted fetal sheep.

Adults who were affected by intrauterine growth restriction (IUGR) suffer from reductions in muscle mass, which may contribute to insulin resistance and the development of diabetes. We demonstrate slower hindlimb linear growth and muscle protein synthesis rates that match the reduced hindlimb blood flow and oxygen consumption rates in IUGR fetal sheep. These adaptations resulted in hindlimb blood flow rates in IUGR that were similar to control fetuses on a weight-specific basis. Net hindlimb glucose uptake and lactate output rates were similar between groups, whereas amino acid uptake was significantly lower in IUGR fetal sheep. Among all fetuses, blood O2 saturation and plasma glucose, insulin and insulin-like growth factor-1 were positively associated and norepinephrine was negatively associated with hindlimb weight. These results further our understanding of the metabolic and hormonal adaptations to reduced oxygen and nutrient supply with placental insufficiency that develop to slow hindlimb growth and muscle protein accretion. Reduced skeletal muscle mass in the fetus with intrauterine growth restriction (IUGR) persists into adulthood and may contribute to increased metabolic disease risk. To determine how placental insufficiency with reduced oxygen and nutrient supply to the fetus affects hindlimb blood flow, substrate uptake and protein accretion rates in skeletal muscle, late gestation control (CON) (n=8) and IUGR (n=13) fetal sheep were catheterized with aortic and femoral catheters and a flow transducer around the external iliac artery. Muscle protein kinetic rates were measured using isotopic tracers. Hindlimb weight, linear growth rate, muscle protein accretion rate and fractional synthetic rate were lower in IUGR compared to CON (P<0.05). Absolute hindlimb blood flow was reduced in IUGR (IUGR: 32.9±5.6mlmin-1 ; CON: 60.9±6.5mlmin-1 ; P<0.005), although flow normalized to hindlimb weight was similar between groups. Hindlimb oxygen consumption rate was lower in IUGR (IUGR: 10.4±1.4μmolmin-1 100g-1 ; CON: 14.7±1.3μmolmin-1 100g-1 ; P<0.05). Hindlimb glucose uptake and lactate output rates were similar between groups, whereas amino acid uptake was lower in IUGR (IUGR: 1.3±0.5μmolmin-1 100g-1 ; CON: 2.9±0.2μmolmin-1 100g-1 ; P<0.05). Blood O2 saturation (r2 =0.80, P<0.0001) and plasma glucose (r2 =0.68, P<0.0001), insulin (r2 =0.40, P<0.005) and insulin-like growth factor (IGF)-1 (r2 =0.80, P<0.0001) were positively associated and norepinephrine (r2 =0.59, P<0.0001) was negatively associated with hindlimb weight. Slower hindlimb linear growth and muscle protein synthesis rates match reduced hindlimb blood flow and oxygen consumption rates in the IUGR fetus. Metabolic adaptations to slow hindlimb growth are probably hormonally-mediated by mechanisms that include increased fetal norepinephrine and reduced IGF-1 and insulin.

Grazing on microcystin-producing and microcystin-free phytoplankters by different filter-feeders: implications for lake restoration

We studied grazing on the green alga Scenedesmus obliquus and the cyanobacterium Planktothrix agardhii (a microcystin-producing and a microcystin- free strain) by three different filter-feeders to compare the efficiency with which these grazers remove Planktothrix from the water. The filterfeeders were two mussel species (the invasive species Dreissena polymorpha and the native Anodonta anatina) and one zooplankton species (Daphnia galeata). On a weight-specific basis, D. galeata had the highest observed clearance rates and A. anatina the lowest. However, D. galeata was only able to feed on Scenedesmus and not on Planktothrix, probably as a consequence of the morphology of Planktothrix (filaments), since neither microcystin-producing nor microcystin-free strains were grazed by Daphnia. Both mussel species were able to graze on Planktothrix, irrespective of microcystin content. Dreissena showed an especially high clearance rate. On an individual basis, however, Anodonta showed the highest clearance rates, which are a consequence of its large biomass. Densities of Anodonta in the field, however, are presently too low to exert a high grazing pressure on the phytoplankton. We suggest therefore that water managers, who may be interested in using filter-feeders as a biomanipulation tool, focus on the improvement of settlement conditions for native bivalves, such as Anodonta, instead of exotic species like Dreissena.

Activity of digestive enzymes along the gut of juvenile red abalone, Haliotis rufescens, fed natural and balanced diets

Two carbohydrases (cellulase, lysozyme), three proteases (trypsin, aminopeptidase and non-specific protease), a non-specific lipase, and semiquantitative tests of 19 digestive enzymes were assayed in different gut sections of juvenile red abalone, Haliotis rufescens, in order to identify the regions where digestion takes place and investigate the extent to which diet composition can modify the digestive capacity of abalone. The abalone were fed either fresh kelp (K) or balanced diets containing 25 or 38% crude protein for 6 months. Enzyme assays were carried out on different sections of the abalone's gut at the end of this period. On a weight-specific basis, the digestive gland was the site containing most of the enzymes. On a protein-specific basis, two main digestion regions were identified: the digestive gland-stomach region that is characterized by high activities of cellulase and lysozyme, chymotrypsin and protease, and the mouth-intestine region with a typically high activity of lipase and amino peptidase. Significant dietary effects were observed on the activity of enzymes, especially in the digestive gland. Abalone fed with 25 and 38% crude protein diets exhibited higher cellulase (39.8 ± 4.6 and 14.2 ± 0.8 mU mg − 1 protein, respectively) and lysozyme activities (88.0 ± 20.4 and 56.6 ± 15.7 U, respectively) than those fed with fresh kelp (5.5 ± 0.7 mU mg − 1 protein and 17.1 ± 1.8 U). In contrast, higher protease activity was found in kelp-fed organisms (234.1 ± 20.4 μg product/mg protein) than those fed the 25 and 38% crude protein diets (109.5 ± 20.7 and 119.5 ± 20.5 μg product/mg protein, respectively). Semiquantitative API ZYM assays resulted in no clear food-specific effects on the activity of carbohydrases, proteases, ester hydrolases or phosphohydrolases, yet organ-specific differences were conspicuous in various cases, and generally agreed with quantitative results. It is suggested that the increased carbohydrase activity exhibited by organisms fed the balanced diets resulted from a combination of an increased number of resident bacteria in the abalone's gut and facilitated contact between dietary substrates and digestive cells. The present results indicate that H. rufescens can adjust their enzyme levels in order to maximize the acquisition of dietary protein and carbohydrates. This characteristic can be advantageously used to search for suitable diets in abalone aquaculture.

Food consumption and absorption efficiency by newly settled summer flounder, Paralichthys dentatus (Linneaus, 1766)

As part of a project to determine the energetic basis of growth rate variation, 24-h experiments were conducted to investigate differences in rates of food consumption and absorption efficiency, between and within cohorts (defined here as offspring from a single set of parents) of newly settled laboratory-reared summer flounder, Paralichthys dentatus (Linneaus, 1766). Food consumption, absorption efficiency and growth were measured for fish which had been fast-growing and slow-growing larvae (referred to as grade 1 and grade 3 fish, respectively) from each of five sets of parents (referred to as cohorts 1, 2, 3, 4 and 5) at constant temperature (20±1 °C), salinity (30±2‰) and light regime (16L:8D), at fish sizes of 15, 20, 25 and 30 mm total length (range: 2.9–59.0 mg dry weight).Significant differences in the rates of consumption of brine shrimp (Artemia sp.) nauplii, on both a per-fish basis (447–5105 nauplii (day)−1) and a weight-specific basis (12–49% body weight (day)−1), absorption efficiency (46–96% of the consumed ration), and specific growth rate (1.08–10.79% body weight (day)−1) existed among fish at each size. Significant differences were also found in food consumption between grade 1 and grade 3 fish within a cohort, although not at all fish sizes. There was no overall effect of cohort on food consumption (p=0.083); however, significant differences in absorption efficiency among cohorts existed (p=0.000). As expected, this study suggests that differences in the rates of food consumption directly influence growth rate variation in this species.

Information on Selected Water Quality Characteristics for the Production of Black Sea Bass, Centropristis striata, Juveniles

Recent interest in the culture of black sea bass, Centropristis striata, has led to questions regarding the environmental requirements of this species for economically-viable production. Here, we present the results of short-term laboratory studies on ammonia toxicity, nitrite toxicity and oxygen consumption rates. Fifty percent of the juveniles died when exposed to 0.7-0.8 mg/L un-ionized ammonia-N for 24 hours (25°C, 23 g/L salinity). All exposed fish survived exposure to ≤ 0.6 mg/L un-ionized ammonia-N for 10 days. Black sea bass juveniles survived 24-hours exposure to 250 mg/L nitrite-N when exposed in 12 or 20 g/L salinity. Fish exposed for 24 hours to nitrite in 35 g/L salinity died when exposed to 250 mg/L nitrite-N, but survived exposure to 100 g/L nitrite-N. All fish exposed to 50 mg/L nitrite-N for 10 days survived (salinities of 12, 20 and 35 g/L). Mean oxygen consumption rate was 0.09 mg/hour/g (25°C). Fish weight significantly affected oxygen consumption rate with larger fish consuming less oxygen per unit time on a weight-specific basis. No treatment effect was observed due to salinity or dissolved oxygen concentration. The information reported here in combination with previous reports provides insight into the environmental requirements of black sea bass culture.

Protein and Amino Acid Metabolism in the Fetal-Placental Unit

After completing this article, readers should be able to: 1. Determine the rate of fetal nitrogen accretion and compare it with the fetal growth rate. 2. Characterize fetal urea production on a weight-specific basis. 3. Explain the effects of hypoglycemia on the fetus. 4. Explain the effects of intrauterine growth retardation on the fetal amino acid profile. Protein synthesis and accretion are the cornerstones of growth that provide the structural framework and enzymatic machinery necessary for fetal development. The maternal uterine circulation supplies the components that the fetus uses for protein accretion. All are derived from the maternal diet or maternal tissue stores. It is important to explore the regulatory processes within the maternal, placental, and fetal compartments that determine fetal amino acid retention. In addition to tissue synthesis, use of free amino acids as oxidative fuel is extensive in the well-nourished fetus and increases significantly during periods of maternal food deprivation. The changes in fetal amino acid utilization represent a significant mechanism by which the fetus adapts to energy deprivation. Before examining the available data, it is necessary to understand the models and methodology by which the data are derived. In general, four methods have been applied to fetal nitrogen metabolism: 1) carcass analysis, 2) net umbilical uptake determinations, 3) measurement of the rate of incorporation of a tracer amino acid into fetal protein, and 4) studies of the kinetics of amino acids in the fetal arterial free amino acid pool. Many studies have combined aspects of two or more of the these methods. ### Carcass Analysis For this method, individual fetuses are sacrificed at several points during gestation, and chemical analysis is performed on the carcass. The total amount of nitrogen, amino acid, or protein at that point in gestation can be determined. Data from individual fetuses are pooled to obtain an accretion curve. This …

Placental glucose transport in growth-restricted pregnancies induced by overnourishing adolescent sheep.

Glucose clamp procedures were used to determine whether the slowing of fetal growth during the final third of gestation in overnourished adolescent ewes is due to a reduction in placental glucose transport capacity. Singleton pregnancies to a single sire were established by embryo transfer and thereafter adolescent dams were offered a high (n = 11) or moderate (n = 7) nutrient intake. Studies were conducted at 130 +/- 0.5 days gestation. Uterine and umbilical blood flows were studied by the steady-state transplacental diffusion technique and glucose fluxes quantified by the Fick principle. To determine the relationship between the transplacental glucose gradient and umbilical (fetal) glucose uptake, studies were conducted with maternal arterial glucose clamped at 5 micromol ml(-1) and fetal glucose at spontaneously occurring and two additional higher levels. Maternal body weight gain during gestation averaged 282 and 57 g day(-1) for high- and moderate-intake dams, respectively. Total placentome weight (209 +/- 23 vs. 386 +/- 34 g) and fetal weight (3072 +/- 266 vs. 4670 +/- 196 g) were lower (P < 0.001) in high- than in moderate-intake groups. The growth-restricted pregnancies in the high-intake dams were associated with reduced uterine (P < 0.05) and umbilical (P < 0.02) blood flows and, in the non-perturbed state, the fetuses were relatively hypoxic (2.1 vs. 3.0 micromol ml(-1), P < 0.05) and hypoglycaemic (0.90 vs. 1.31 micromol ml(-1), P < 0.002). Linear regression analysis of umbilical glucose uptake at three steady-state uterine-umbilical arterial transplacental plasma glucose concentration gradients revealed that absolute placental glucose transport capacity was lower in high- than in moderate-intake dams (mean slope, 0.8 vs. 1.5 dl min(-1), P < 0.05; and mean intercept, 1.84 vs. 3.40 micromol ml(-1)). However, glucose transfer capacity was not different between the two groups when expressed on a placental weight-specific basis. This confirms that the small size of the placenta per se is the major limitation to placental glucose transfer in the overnourished adolescent pregnant sheep.

Regulation of 11 beta-hydroxysteroid dehydrogenase type 2 activity in ovine placenta by fetal cortisol.

The effect of fetal cortisol on the activity of the type 2 isoform of the enzyme, 11 beta-hydroxysteroid dehydrogenase (11 beta-HSD2), was examined in ovine placenta and fetal kidney by measuring tissue 11 beta-HSD2 activity during late gestation when endogenous fetal cortisol levels rise and after exogenous cortisol administration to immature fetuses before the prepartum cortisol surge. Placental 11 beta-HSD2 activity decreased between 128-132 days and term (approximately 145 days of gestation) in association with the normal prepartum increase in fetal plasma cortisol. Raising fetal cortisol levels to prepartum values in the immature fetus at 128--132 days of gestation reduced placental 11 beta-HSD2 activity to term values. In contrast, 11 beta-HSD2 activity in the fetal renal cortex was unaffected by gestational age or cortisol infusion. When all the data were combined, there was an inverse correlation between the log fetal plasma cortisol level at delivery and placental 11 beta-HSD2 activity, expressed both on a weight-specific basis and per mg placental protein. Fetal cortisol therefore appears to be a physiological regulator of placental, but not renal, 11 beta-HSD2 activity in fetal sheep during late gestation. These findings have important implications, not only for glucocorticoid exposure in utero, but also for the local actions of cortisol within the placental tissues that are involved in initiating parturition in the sheep.

F60Umbilical vein blood flow in growth restricted fetuses

ObjectiveThe present study was designed to determine whether specific umbilical blood flow is reduced in IUGR fetuses.SubjectsThirty‐seven IUGR fetuses of different clinical severity were examined by Doppler ultrasound within four hours of the last nonstress test prior to delivery.MethodAbsolute and weight specific umbilical vein (UV) flow were calculated from measurements of UV diameter and UV mean velocity. UV diameter, velocity and UV flow were calculated also per unit head (HC) or abdominal circumference (AC) and correlated with gestational age.ResultsUV flow per kilogram was significantly lower in the more severe IUGR fetuses (abnormal umbilical arterial p.i.) than in normal comparable fetuses (P &lt; 0.001). UV flow per unit head circumference was significantly lower in the three groups (P &lt; 0.001) than in the control population. The UV diameter/HC was normal whereas UV velocity/HC was significantly lower in IUGR fetuses than in comparable controls.ConclusionsThe present study clearly establishes that umbilical venous blood flow is reduced in IUGR fetuses on a weight specific basis. The sonographic growth parameter which best distinguishes umbilical flow differences of IUGR fetuses from normal fetuses is the head circumference.

Effects of birth weight and postnatal nutrition on neonatal sheep: I. Body growth and composition, and some aspects of energetic efficiency.

We investigated the effects of birth weight and postnatal nutrition on growth characteristics of neonatal lambs. Low- and high-birth-weight male lambs were individually reared on a high-quality liquid diet to grow rapidly (ad libitum access to feed) or slowly (ADG 150 g) to various weights up to 20 kg live weight (LW). Average daily gain tended to be greater in the high- (mean+/-SE 345+/-14 g) than in the low- (329+/-15 g) birth-weight lambs given ad libitum access to feed owing to slower growth by the small newborns during the immediate postpartum period. At birth, on a weight-specific basis, small newborns contained 6.4% less nitrogen and tended to have more ash (8.9%) than the high-birth-weight newborns. Daily rates of fat, ash, and GE accretion were greater, and nitrogen accretion tended to be greater in the rapidly grown large newborns than in their small counterparts. At any given empty body weight (EBW) during rearing, low-birth-weight lambs contained more fat and less ash, resulting in slowly and rapidly grown small newborns containing 39.3 and 42.7 Mcal GE, respectively, at completion of the study (17.5 kg EBW), compared with 34.8 and 40.5 Mcal in their large counterparts. The differences in fatness and energy content between the birth weight categories are attributed to energy requirements for maintenance that were approximately 30% lower, coupled with higher relative intakes in the low-birthweight lambs, during the early postnatal period. At this time, the ability to consume nutrients in excess of lean tissue growth requirements was apparently more pronounced in small than in large newborns, which resulted in lower efficiency of energy utilization for tissue deposition. Furthermore, body composition differences between the slowly and rapidly reared lambs support the notion of a priority of lean tissue over fat when nutrient supply is limited.

The effect of body size on the standard metabolic rate of the lesser spotted dogfish

Standard metabolic rates were measured as the rate of oxygen consumption in 33 Scyliorhinus canicula, ranging in weight from 3–929 g. The amount of oxygen consumed per hour (Vo2) changed predictably with body size according to the relationship Vo2=0–104 W0.855, where W represents fish weight in g. On a weight specific basis, the level of standard metabolism in juvenile dogfish (5 g) was nearly double that measured in adults (500 g).

Plasma disposal rate and hepatic alanine metabolism in pregnant and nonpregnant rabbits.

To better define the glucose-alanine relationship and hepatic alanine metabolism during pregnancy, glucose and alanine turnover rates (TR) and simultaneous hepatic alanine uptake were determined in nine term pregnant (P) and 12 nonpregnant (NP) rabbits who had undergone chronic catheterization of both the systemic and hepatic circulations. [U-14C3]Alanine and [3-3H1]glucose were used as tracers. Whole animal [U-14C3]alanine TR was significantly greater in P than in NP animals (42.7 +/- 1.7 versus 31.9 +/- 1.8 mumol.min-1, respectively, p < 0.001). However, there was no difference when the alanine TR was compared on a weight-specific basis (11.3 +/- 0.6 versus 9.6 +/- 0.6 mumol.min-1.kg-1). The glucose TR was higher in P compared with NP rabbits on both an absolute (122.3 +/- 6.2 versus 79.8 +/- 5.8 mumol.min-1, p < 0.001) and a weight-specific basis (32.9 +/- 1.4 versus 24.0 +/- 1.9 mumol.min-1.kg-1, p < 0.005). Although the fraction of plasma glucose derived from plasma alanine in the whole animal was similar in P and NP animals (16.7% +/- 1.4 versus 13.9 +/- 0.7%, respectively), the absolute amount of plasma glucose derived from plasma alanine was greater in P rabbits (20.8 +/- 1.8 versus 11.2 +/- 1.2 mumol.min-1, p < 0.0005). In addition, the percentage of plasma alanine being converted to plasma glucose was greater in P than in NP animals (48.1 +/- 2.6 versus 34.6 +/- 2.0%, p < 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Drinking rates and Na+ effluxes in response to temperature change in two species of marine flatfish: dab, Limanda limanda and plaice, Pleuronectes platessa

The relationship between fish mass and drinking rate in two species of flatfish, dab and plaice, weighing between 1 and 150 g was investigated. Both plaice and dab showed increased drinking rates with increasing fish mass, although — when calculated on a weight-specific basis — the increase was negligible. Fish were acclimated to winter and summer temperatures of 9 and 14°C, respectively. In winter both species were acutely transferred to 5, 14 and 21°C and in summer to 5, 9, 21 and 25°C. Drinking rates, Na+ efflux and body ion content were measured. Dab showed lower drinking rates than plaice (e.g. the weight-specific drinking rates of summer-and winter-acclimated dab were 0.12±0.01 and 0.06±0.006 ml·h-1·100 g-1, respectively, compared to that of plaice which were 0.25±0.02 ml·h-1·100 g-1 in summer and 0.17±0.02 ml·h-1·100g-1 in winter). Summer dab exhibited decreased weight-specific drinking rates at 5, 9 and 25°C, while winter dab increased drinking at 21°C. Winter plaice also showed increased drinking at 21°C and a decrease at 5°C, but in contrast summer plaice did not increase drinking at either 21 or 25°C but showed a decrease at 5 and 9°C. Winter dab and plaice showed similar Na+ efflux rates but summer dab showed higher efflux at all temperatures except 5°C. The data indicates that (a) the osmoregulatory function of plaice is much weaker than that of dab at higher temperatures (>20°C) and (b) mass has a greater effect on drinking and Na+ efflux rates than temperature; although when calculated on a weight-specific basis neither drinking nor efflux showed any variation with fish mass suggesting that these functions occur at similar intensities across the entire weight range.

The effects of thyroid hormones on oxygen and glucose metabolism in the sheep fetus during late gestation.

1. The effects of thyroid hormones on fetal metabolism during late gestation were examined by measuring the rates of glucose and oxygen utilization rates in chronically catheterized sheep fetuses made hypothyroid by either fetal thyroidectomy (TX) or hypophysectomy (HX). The values were compared with those in intact fetuses and in thyroxine (T4)-treated TX and HX fetuses. 2. Umbilical O2 uptake expressed on a weight-specific basis was reduced by 20-30% in the hypothyroid fetuses and was restored to normal values when plasma T4 levels were maintained in the TX and HX fetuses by exogenous T4 administration. 3. The low O2 consumption rates of the untreated hypothyroid fetuses were accompanied by fetal growth retardation, an abnormal blood gas status, and in the TX fetuses, by significant reductions in the rates of glucose oxidation, CO2 production from glucose carbon and O2 utilization for glucose oxidation. 4. When T4 levels were maintained in the TX fetuses, these metabolic rates and fetal blood gas status were restored to their normal values. Replacement of T4 also sustained growth in TX but not in HX fetuses. 5. When the data from all fetuses were combined irrespective of treatment, there were significant positive correlations between plasma levels of T4 (but not triiodothyronine (T3)) and the rates of umbilical O2 uptake, glucose oxidation, CO2 production from glucose carbon and O2 utilization for glucose oxidation in the individual fetuses. 6. These findings demonstrate that T4 is a physiological regulator of O2 utilization by the sheep fetus close to term.

Specific dilatation of coking coals: a means of reconciling the Ruhr and Audibert-Arnu methods

The Ruhr and the Audibert-Arnu methods are two International Standard (ISO) tests for evaluating the caking properties of coal which are widely used in North America and Europe. These two methods are examined with the intent of reconciling the different expansion data. Factors that affect percentage dilatation are discussed. Dilatation is shown to depend primarily on the mass of air-dried coal charged into the retort tube, provided that the heating rate, inside tube diameter, water added to the coal and particle size distribution of the sample are the same. It is found that expansion data reported on an air-dried weight specific basis are nearly method-independent. The experimental work in support of this observation involved dilatation analysis on weighed test specimens (coal pencils), with a known added water content, using both methods.

Glucose metabolism in pregnant sheep when placental growth is restricted.

The effect of restricting placental growth on glucose metabolism in pregnant sheep in late gestation was determined by primed constant infusions of D-[U-14C]- and D-[2-3H]glucose and antipyrine into fetuses of six control sheep and six sheep from which endometrial caruncles had been removed before pregnancy (caruncle sheep). In the latter, placental and fetal weights were reduced, as was the concentration of glucose in fetal arterial blood. Fetal glucose turnover in caruncle sheep was only 52-59% of that in controls, largely because of lower umbilical loss of glucose back to the placenta (38-39% of control) and lower fetal glucose utilization (61-74% of control). However, fetal glucose utilization on a weight-specific basis was similar in control and caruncle sheep. Significant endogenous glucose production occurred in control and caruncle fetal sheep. Maternal glucose production and partition of glucose between the gravid uterus and other maternal tissues were similar in control and caruncle sheep. In conclusion, when placental and fetal growth are restricted, fetal glucose utilization is maintained by reduced loss of glucose back to the placenta and mother and by maintaining endogenous glucose production.

Scaling respiratory pattern and respiratory ‘drive’

We tested three predictions regarding the relationship between body size and respiratory ‘drive’ and timing in mammals. Mechanical considerations had led to the prediction that Te/ Ttot and probably Ti/ Ttot would be interspecific constants. In eleven species of mammals, ranging in size from 0.033 kg to 520 kg, Te/ Ttot during awake quiet breathing was an interspecific constant with a value of 0.65 (±0.004); Ti/ Ttot was 0.345 (±0.004). Given that Te ∝ BW 1.0 (Stahl, 1967), if Te and Ti are ∝ BW 0.28 (Bennett and Tenney, 1982), and if Vt/ Ti is an index of respiratory ‘drive’ should be ∝ BW 0.72, following the same proportionality with body size as does basal metabolic rate (V̇ O 2 ). Data for the same eleven species gave the relationship Vt/ Ti ∝ BW 0.74. Testing further the notion that ‘drive’, on a weight specific basis, is proportional to BW −0.26, we studied the response, %ΔV̇ i, in eleven species to approximately 12% inspired O 2. This ‘output’ of the system in response to a hypoxic stimulus was found to scale with BW −0.27. The question whether this reflects a higher set ‘gain’ of the respiratory controller of smaller animals and/or some feature of the innervation, or intrinsic properties of the respiratory muscles that varies with body size is discussed.

Osmoregulation in Nestling Glaucous-Winged Gulls

-Blood samples from 32 nestling Glaucous-winged Gulls (Larus glaucescens) ranging in age from 1 to 41 days were collected at a nesting site near Vancouver, B.C. The hematocrit was positively correlated, the plasma sodium and chloride concentrations negatively correlated, and the plasma potassium and osmotic concentrations uncorrelated with age. Salt gland secretion was elicited in 23 young gulls by intravenous injection of I M NaC1. The concentration and the volume of secretion increased with age. Sodium secretion was positively correlated with the size of the salt gland. The secretion of potassium and minimum maintained concentrations of sodium were positively correlated with age. In the first hour of secretion, hatchlings eliminated 39% of the injected fluid containing 24% of the injected sodium; in contrast, the oldest nestlings removed 77% of the fluid and 55% of the sodium. Cloacal fluid voided by older salt-loaded birds was less concentrated than that of younger ones. Organ weights were determined in 20 nestlings. Kidney weight was 2-3% of the body weight regardless of age, but the relative weights of the Harderian, salt, and adrenal glands decreased with age. From the time they begin to feed, young marine birds consume foods that are hyperosmotic to their body fluids and must, therefore, eliminate excess solutes (mainly sodium and chloride) in order to remain in osmotic balance. Adult birds of marine species eliminate excess sodium chloride by means of the salt glands (Peaker and Linzell 1975), the secretion of which has roughly twice the concentration of sea water. Thus, they can drink sea water or eat salt-rich foods and still maintain osmotic balance. Adult birds also have other osmoregulatory options: e.g., they can select food items and so, theoretically at least, regulate their salt intake; those living along the coast also have access to fresh water. In contrast, nestlings do not have these choices although their parents could select food of low osmotic concentration or extract salts from it before feeding it to them. However, my observations of the food (often whole small fish or mussels) regurgitated by nestlings suggest that the adults do neither of these things. Nestlings do not ordinarily have access to water, although they have been reported to eat grass, which may provide them with free water (Ensor and Phillips 1972). They may also use dew or the parents may bring them fresh water, although neither of these possibilities seems to have been substantiated. Hence, nestling marine birds probably rely heavily on extrarenal secretion to excrete excess salt. Little has been reported about the rate of maturation of the secretory process or the factors that affect it in such nestlings. Douglas (1968) examined the size and secretory capacity of salt glands from Ad6lie Penguin chicks (Py oscelis adeliae). He found that the gland's weight and secretory rate were linearly correlat d with body size, but that the chloride concentration of the secretion was constant hroughout the growth period. He noted secretion in pipping chicks and suggested that ev n at this age, they were capable of handling the excess salt in their diet of marine inverteb es. Hughes (1968) also found that the salt gland of Common Tern chicks (Sterna hirundo) enlarged in linear fashion with body size, even though older birds were less efficient at excreting imposed salt loads than younger ones. This was due to a decrease in the volume secreted by the salt gland, not in the concentration of the secretion. However, some of the birds in that study were salt-loaded more than once during their growth period and this may have influenced their responses. Ensor and Phillips (1972) compared the secretory capacities of salt glands from 4to 5and 15to 16week-old chicks in two mixed populations of gulls (Larus argentatus and L. fuscus) that had been raised either on a marine island or an inland freshwater site. The younger birds from the marine environment were smaller than their freshwater counterparts and had larger salt glands, nearly twice as large on a weight-specific basis. The secretion of their glands was twice as concentrated in sodium and was produced at three times the rate of that from freshwater birds. These differences disappeared by the time the birds were 15-16 weeks old. In the present study, I examined the blood of birds at representative stages of the entire maturation period for age-related changes in hematocrit, electrolyte concentration, and os-

Temperature and water relations of a parasitic wasp in its free-living adult stage and its phytophagous host

1. 1. Temperature and water relations in the parasitic wasp Anaphes ovijentatus (Crosby and Leonard) (Mymaridae: Hymenoptera), one of the smallest of insects, and its host Lygus hesperus Knight (Miridae: Heteroptera) were studied. 2. 2. LT 50s for the free living adult female wasps were higher (20.63 hr) than those of male wasps (14.68 hr) and 1st instar Lygus nymphs (7.07 hr) at 30°C with an RH of < 5%. 3. 3. Critical thermal maxima were significantly higher in the parasitic wasp (47.6°C) than in its host (45.7°C). 4. 4. Rates of water loss were dependent upon temperature and saturation deficit with evidence of an ability of both species to exercise some control over loss rates under increasingly stressful conditions. 5. 5. Rates of water loss of both species were comparable to those of other xeric-adapted insects on a loss per unit of surface area-specific basis. On a weight-specific basis, rates of water loss for these insects which weigh less than 100 μg were higher than those of larger, xeric-adapted species.

Energetics of a population of Asellus aquaticus (Crustacea, Isopoda): respiration and energy budgets

SUMMARY. Respiration of Asellus aquaticus was determined on tiine occasions throughout the year using a Gilson differential respirometer. On each occasion the determination was made at the lake temperature, which ranged from 2 to 18°C, Linear regressions were derived for log oxygen uptake against log dry weight. There was a significant difference between mean rates of oxygen uptake at the various temperatures but the slopes of the regression lines, which varied from 0,62 to O.85 with a mean of 0,76, were not significantly different.The temperature of the lake was monitored throughout the year. Using the relationship of oxygen uptake against temperature, and estimates of population density obtained previously, the total annual respiration of the population was calculated as 4571 ml O2 m‐2, equivalent to an energy loss of 92.3 kj m‐2 year‐1 from a mean biomassof 752 mg m‐2.Consumption of decayed Alnus glutinosa leaves and faecal production rates, and thus assimilation efficiency, were determined by gravimetric methods in the laboratory at 10°C, close to the mean temperature of the lake (10.rC), In the four size classes investigated, larger animals consumed more food per individual, but less on a weight specific basis. However, it was shown that consumption was greater if the leaf material was more highly decomposed, Assimiliation efficiency was calculated as 23%.Using data for respiration, population density and the assimilation efficiency, the annual population energy budget was estimated as (kJ m‐2year‐1): consumption, 568.9 (100%); production, 38.5 (6.8%); respiration, 92.3 (16.2%); faeces, 438.1 (77%). The significance of these energy values, and the ecological efficiencies calculated from them, are discussed in relation to other published work.