Phenotypic flexibility of a southern African duck Alopochen aegyptiaca during moult: do northern hemisphere paradigms apply?

Phenotypic flexibility during moult has never been explored in austral nomadic ducks. We investigated whether the body condition, organ (pectoral muscle, gizzard, liver and heart) mass and flight‐feather growth Egyptian geese Alopochen aegyptiaca in southern Africa show phenotypic flexibility over their 53‐day period of flightless moult. Changes in body mass and condition were examined in Egyptian geese caught at Barberspan and Strandfontein in South Africa. Mean daily change in primary feather length was calculated for moulting geese and birds were dissected for pectoral muscle and internal organ assessment. Mean body mass and condition varied significantly during moult. Body mass and condition started to decrease soon after flight feathers were dropped and continued to do so until the new feathers were at least two‐thirds grown, after which birds started to regain body mass and condition. Non‐moulting geese had large pectoral muscles, accounting for at least 26% of total body mass. Once moult started, pectoral muscle mass decreased and continued to do so until the flight feathers were at least one‐third grown, after which pectoral muscle mass started to increase. The regeneration of pectoral muscles during moult started before birds started to gain overall body mass. Gizzard mass started to increase soon after the onset of moult, reaching a maximum when the flight feathers were two‐thirds grown, after which gizzard mass again decreased. Liver mass increased significantly as moult progressed, but heart mass remained constant throughout moult. Flight feather growth was initially rapid, but slowed towards the completion of moult. Our results show that Egyptian geese exhibit a significant level of phenotypic flexibility when they moult. We interpret the phenotypic changes that we observed as an adaptive strategy to minimize the duration of the flightless period. Moulting Egyptian geese in South Africa undergo more substantial phenotypic changes than those reported for ducks in the northern hemisphere.     

Body condition changes of sand martins (Riparia riparia) during breeding, and a comparison with fledgling condition

The body condition of adult sand martins during the breeding season and a sample of fledglings was investigated by carcass analysis and by examination of live birds in the field. Fat scoring of live individuals was a reliable predictor of an individual's lipid content in most instances. Body mass changes during breeding were related to changes in the size of birds' lipid reserves, pectoral muscle mass, body water, and to development of the reproductive system. In both males and females, reserve lipid declined between the onset of breeding and nestling rearing. Pre-breeding males had significantly greater pectoral muscle masses than did nestling rearing females. The potential significance of protein in pectoral muscles as an energy reserve during breeding was small compared with lipid reserves. By comparing potential energy reserves in body lipid and protein with daily energy expenditure, it was calculated that neither incubating nor nestling rearing adults could survive a day of normal activity without feeding. The selective premium on adults optimizing their use of time and energy for self-maintenance behaviour during breeding is therefore likely to be great.     

Thermogenic side effects to migratory predisposition in shorebirds

In the calidrine sandpiper red knot (Calidris canutus), the weeks preceding takeoff for long-distance migration are characterized by a rapid increase in body mass, largely made up of fat but also including a significant proportion of lean tissue. Before takeoff, the pectoral muscles are known to hypertrophy in preparation for endurance flight without any specific training. Because birds facing cold environments counterbalance heat loss through shivering thermogenesis, and since pectoral muscles represent a large proportion of avian body mass, we asked the question whether muscle hypertrophy in preparation for long-distance endurance flight would induce improvements in thermogenic capacity. We acclimated red knots to different controlled thermal environments: 26 degrees C, 5 degrees C, and variable conditions tracking outdoor temperatures. We then studied within-individual variations in body mass, pectoral muscle size (measured by ultrasound), and metabolic parameters [basal metabolic rate (BMR) and summit metabolic rate (M(sum))] throughout a 3-mo period enclosing the migratory gain and loss of mass. The gain in body mass during the fattening period was associated with increases in pectoral muscle thickness and thermogenic capacity independent of thermal acclimation. Regardless of their thermal treatment, birds showing the largest increases in body mass also exhibited the largest increases in M(sum). We conclude that migratory fattening is accompanied by thermoregulatory side effects. The gain of body mass and muscle hypertrophy improve thermogenic capacity independent of thermal acclimation in this species. Whether this represents an ecological advantage depends on the ambient temperature at the time of fattening.     

Water balance in Rhodnius prolixus during flight: Quantitative aspects of diuresis and its relation to changes in haemolymph and flight-muscle water

The amount of water voided by male Rhodnius prolixus which were flown to exhaustion varied from 0 to over 10% of the initial live weight. It accounted for nearly all of the body water lost during the flight period. Simultaneous measurements on the loss of haemolymph water and an estimate of the amount of faecal water in the excreta indicated that the source of the voided water was primarily the haemolymph. The total water content of the flight muscles changed very little in insects which flew to exhaustion. It is concluded that, despite the diuresis and loss of water, and the considerable reduction in haemolymph volume, dehydration of the flight muscles of male R. prolixus does not occur during these flight periods, and is not a factor contributing to ‘exhaustion’. The possibility that insufficient haemolymph is a factor limiting the duration of flight is discussed.     

Body protein does not vary despite seasonal changes in fat in the White Stork Ciconia ciconia

To understand how a large soaring bird, the White Stork Ciconia ciconia , copes with energy constraints, we compared changes in body mass in 14 captive adult storks with the body composition of 12 free-ranging adult storks found dead from accidents. The captive storks, already in an enclosure for several years, were fed ad libitum . They were weighed daily for 1.53.5 years using an automatic device. The bodies of the accidentally killed storks were analysed to determine total water, lipid, protein and ash contents, and to assess the biochemical composition of certain organs. Females were on average 20% lighter and 24% smaller than males, but the body mass of the sexes varied in parallel throughout the year. Body mass peaked in December and January (2530% above minimal body mass), due essentially to large fat stores in subcutaneous and abdominal adipose tissues. Body mass and body lipid rapidly decreased from February to June, whether the storks reared chicks successfully or not, and remained minimal for a few days into July. In contrast to birds using flapping flight, no variation in body protein or pectoral muscle protein was observed while breeding, even though the moult occurred then, nor in August, before the time when wild storks migrate. An endogenous regulation of body fuels is discussed.     

Geographical variation of protein reserves in birds: the pectoral muscle mass of Dunlins Calidris alpina in winter

Pectoral muscle size (as an index of protein reserves) was measured in Dunlins during midwinter on five British estuaries, and examined in relation to latitude and midwinter air temperature. In adults, pectoral muscle size was greater on more northerly and colder estuaries. Pectoral muscle size of juveniles varied less than that of adults between estuaries. For both ages, pectoral muscle size correlations were stronger with temperature than with latitude. The size of protein reserves in the pectoral muscles differed by 26% (adults) and 14% (juveniles) between warmest (Menai Straits) and coldest (Firth of Forth) sites studied. Both pectoralis major and supracoracoideus muscles contributed to the protein store, but the supracoracoideus formed only 12% of the total pectoral muscle mass. The age-difference appeared not to arise through the selective death of some juveniles. We propose that juveniles have a set-point for pectoral muscle size in winter adapted to the broad geographical area within which they may settle. The set-point may then be altered according to the weather conditions experienced at the site where they settle and return as adults.     

Muscle volume, MRI relaxation times (T2), and body composition after spaceflight.

Postflight changes in muscle volume, calf muscle transverse relaxation time, and total body composition were measured in 4 crewmembers after a 17-day mission and in 14-16 crewmembers in multiple shuttle/Mir missions of 16- to 28-wk duration. During the 17-day mission, all muscle regions except the hamstrings significantly decreased 3-10% compared with baseline. During the shuttle/Mir missions, there were significant decreases in muscle volume (5-17%) in all muscle groups except the neck. These changes, which reached a new steady state by 4 mo of flight or less, were reversed within 30-60 days after landing. Postflight swelling and elevation of calf muscle transverse relaxation time persisted for several weeks after flight, which suggests possible muscle damage. In contrast to the 17-day flight, in which loss in fat, but not lean body mass, was found (25), losses in bone mineral content and lean body mass, but not fat, were seen after the longer shuttle/Mir missions. The percent losses in total body lean body mass and bone mineral content were similar at approximately 3.4-3.5%, whereas the pelvis demonstrated the largest regional bone loss at 13%.     

Flightless rails endemic to islands have lower energy expenditures and clutch sizes than flighted rails on islands and continents

Data are presented on the standard energetics of six flighted and five flightless species of rails (Aves: Rallidae). The factors influencing these data and those from three additional species available from the literature, one of which was flightless, are examined. Basal rate of metabolism correlates with body mass, residency on islands or continents, volant condition, pectoral muscle mass, and food habits, but not with climate. The greatest capacity (96.2%) to account for the variation in basal rate of metabolism in 15 populations that belong to the 14 species occurs when body mass, volant condition, and food habits are combined. Then flighted species have basal rates that average 1.38 times those of flightless species and herbivorous rails have basal rates that are 1.37 times those of omnivorous species, which means that, independent of body mass, flighted gallinules have basal rates that are 1.9 times those of flightless, omnivorous rails. Distribution, pectoral muscle mass, and flight ability cannot be combined in the same analysis because they code for similar information. The evolution of a flightless condition in rails requires the absence of eutherian predators, but has occurred in the presence of marsupial predators. Each of the six studied flightless rails independently evolved a flightless condition and a low basal rate, whereas the evolution of herbivory and an associated high basal rate evolved at least twice in these species. Flightless rails on islands have clutch sizes that are only about one-half those of flighted rails living on continents, the reduction in clutch size correlating with a reduction in basal rate of metabolism. Thermal conductance in rails is correlated with body mass and food habits: herbivorous rails had conductances that were 1.43 times those of omnivores, i.e., conductances are highest in species with the highest basal rates.     

Body weight, gonad development and moult in the Tawny owl (Strix alum)

Gonad development, moult and seasonal changes in body weight and composition in the Tawny owl Strix aluco were studied by examining the carcasses of 369 owls (mostly road casualties) supplemented by 112 weights of live birds. In breeding females laying was preceded by the accumulation of fat and to a lesser extent protein which meant that they weighed more at this time (February/March) than at any other. Females declined in weight after laying but were still heavy during incubation. In contrast, males and non-breeding females did not increase in weight before the start of the breeding season. Juveniles reached or even exceeded adult weight well before independence due to the deposition of fat. Even after the exclusion of diseased or contaminated individuals, 9·4% of the birds examined were identified as starving; most of these were in the autumn and were probably newly-independent young wandering in search of territories. In both sexes gonad maturation was of brief duration coinciding with the period (mid-March to mid-April) in which eggs are normally laid. Ovarian growth was biphasic. In the three months prior to the breeding season ovarian condition in different birds was positively correlated with body weight and it appeared that the largest ovarian follicles of females in poor condition failed to attain the size from which rapid growth to final ovulation occurs. in males testis size in the breeding season was correlated with pectoral muscle weight (an index to protein condition) but not body weight. The majority of adults commenced wing moult in June. The average duration of primary moult was estimated to be 77 days. Healthy birds replaced the primaries of both wings at the same rate but most diseased birds moulted asymmetrically and/or out of season. First-year birds renewed their body feathers between September and November. In the Tawny owl territory establishment, breeding and moult are temporally separated.     

Enzymes of heterotherms: LDH of hibernating and normothermic little brown bats, Myotis lucifugus.

1. Lactate dehydrogenase (LDH) was isolated from pectoral or flight muscle, liver and heart of hibernating and normothermic bats, Myotis lucifugus. 2. Activities at high substrate concentrations and the interactions between substrate and enzyme were studied to evaluate possible adaptations associated with the extended period of depressed metabolism of this bat. 3. Activity levels in all tissues decreased with hibernation, although the magnitude was dependent upon both temperature and substrate concentration. In general, the extent of decrease was in the order pectoral muscle greater than liver much greater than heart. 4. No correlation was found between the temperature sensitivity of the tissue LDHs as estimated by Ea-values, and the physiological state. 5. However, affinity parameters as estimated by Km-values were less temperature sensitive in hibernator tissues in contrast to the marked perturbations exhibited at temperature extremes in the normotherm enzymes. 6. It is suggested that changes in subunit quantities are in part responsible for these kinetic differences, and not major qualitative isozyme changes. 7. The net result of these effects is a reduced carbon flux to lactate during hibernation, but the maintenance of a potential for LDH catalyses during arousal.     

THE LEVEL OF RESERVE PROTEIN AS THE PROXIMATE FACTOR CONTROLLING THE TIMING OF BREEDING AND CLUTCH-SIZE IN THE RED-BILLED QUELEA QUELEA QUELEA

Changes in the fat and flight muscle protein reserves of adult Red-billed Queleas Quelea quelea were followed in two colonies in Tanzania and Botswana. At the start of a breeding attempt the protein reserves were higher that at any other time of the year, particularly in females which had heavier flight muscles (non-fat dry weight) than did the (larger) males at that time. The pre-breeding increase in the labile component of the muscle protein (the actual protein reserve) is calculated at 80% for females, but only 14% for males. The fat reserve was only increased slightly at the beginning of the breeding attempt.
In both sexes, though for different reasons, the protein and fat reserves fell rapidly during the first few days of the attempt, in some individuals to dangerously low levels. During the incubation period there was rapid recovery while the situation during the rearing period appeared to vary between colonies.
It is proposed that the proximate control of breeding is provided by the individual's own body condition, and particularly the state of its protein reserves. No environmental releasers are required for the birds to breed at the appropriate time of the year.
Individual females producing two, three and four egg clutches differed in the rate at which their reserves fell during egg formation. The results are used to support the view that in this quelea the actual clutch-size produced on any occasion is the largest the female can produce before becoming too enfeebled. Thus, clutch-size appears to be determined phenotypically downward from a maximum which is indirectly under genetic control.     

Fat and body condition in migrating Redwings Turdus iliacus

During the night of 29–30 October 1995, over 600 Redwings Turdus iliacus died as a result of flying into the lighthouse at Bardsey, Gwynedd, North Wales. These migrating birds were used to investigate fat levels in relation to age, sex, biometrics and pectoral muscle mass. Wing length was the best single linear measure of size and mean wing length of males was 2.5 mm greater than that of females. Body mass of the casualties declined during the night and the mean body mass of birds arriving towards the end of the night was 1.5 g lower than that of the first arrivals. Fat deposits at different body sites were significantly correlated with each other and with body mass, and, by extrapolation, the mass of intra-abdominal fat remaining would be significant when other fat deposits have been depleted. Fat in the tracheal pit (the claviculo-coracoid fat body) demonstrated the best correlation with body mass and was linearly correlated with visual fat scores. Fat was also present in the pectoral muscle but did not make a significant contribution to overall body mass. Two-thirds of the variation in body mass was accounted for by wing length, the mass of claviculo-coracoid fat and the lean-dry mass of pectoral muscle. Claviculo-coracoid fat and lean pectoral-muscle mass contributed independently to overall body mass. These data support the view that increase in fat in relation to migration is accompanied by an increase in protein or lean muscle mass, but suggest that these are controlled independently.     

Bluegill Lepomis macrochirus synchronize pectoral fin motion and opercular pumping

The relative timing between operculum and pectoral fin motion was examined in swimming bluegill Lepomis macrochirus to determine if respiratory fluid flows from the operculum might have an effect on flow over the pectoral fin. Five bluegill were filmed swimming at speeds from 0·5 to 1·5 body (total) lengths s⁻¹. The timing of opercular pumping and pectoral fin beating was noted and analysed using circular statistics. Fish tended to ventilate their gills every second or third pectoral fin beat. While locomotion and ventilation had different frequencies, however, they were synchronized: fish maintained a consistent phase relationship between them. Thus, within pectoral fin beats when the operculum pumps, the jet consistently occurred during pectoral fin abduction, ending just after the fin was fully abducted and beginning adduction. Based on the distance between the opercular slit and the pectoral fin base, the jet was estimated to reach the fin during maximum abduction. Dye flow visualization confirmed this estimate, revealing that the opercular flow wraps around the base of the fin during peak abduction, when it is likely to have little hydrodynamic effect.     

Body size and composition of elephant seals (Mirounga leonine): absolute measurements and estimates from bone dimensions

The major body components (bone, muscle, blubber, viscera and connective tissue) of 94 elephant seals were dissected and weighed.
Seals in growth phase 3 (more than ten weeks old) had significantly more muscle and viscera and less blubber than seals in growth phases 1 and 2 (less than ten weeks old) of similar body weight. There were no significant differences in body composition between sexes before sexual maturity, but after sexual maturity was attained males had relatively more muscle, and less bone and viscera, than females.
Prediction equations relating body component weight and body weight were derived by regression analysis. These were very highly significant, and could be used to estimate body composition from body weight.
It was demonstrated that body length could be estimated from linear measurements of some bones, which would enable an estimate of size and composition of seals to be made from bone dimensions.     

Myoglobin levels and mATPase activity in pectoral muscles of spruce and ruffed grouse (Aves: Tetraoninae)

Myoglobin concentration and myosin ATPase activity were measured in the pectoral muscle of wild spruce grouse (Dendragapus canadensis) and ruffed grouse (Bonasa umbellus), together with the weight of the Mm. pectoralis, supracoracoideus and heart. mATPase activities were similar in both species, but spruce grouse contained 15 times more myoglobin in the pectoralis muscle and the heart was three times heavier than that of the ruffed grouse. The relative mass of the flight muscles and wing loading were similar between species. Characteristics of the pectoral muscle of both grouse species reflect adaptations to predation and advertising displays. The glycolytic nature of the ruffed grouse pectoral muscle and small heart size is an adaptation to a sedentary existence within a small home range. The more oxidative pectoral muscle of spruce grouse together with its larger heart are adaptations to seasonal dispersals requiring more sustained flight.     

The relationship between body condition and the timing of implantation in pregnant Grey seals (Halichoerus grypus)

Adult female Grey seals were sampled from the Farne Islands, Northumbria at monthly intervals during 1980 and 1981. The mean date of implantation was 7 April and most females implanted between 11 March and 5 May. Sculp, core and total body weights declined most at the time of lactation in November and were lowest during February. These weights increased most rapidly during March and April; at the same time as implantation occurred. The pectoral blubber depth followed a similar pattern. Females in which the spring increase in body condition occurred earliest also had the earliest implantation. The study demonstrates a correlation between body condition and the time of implantation.     

大鳍异鰔年龄与生长

于2013年11月至2014年9月, 在怒江、槟榔江和龙川江共采集大鳍异鲦(Creteuchiloglanis macropterus)230尾, 对其年龄与生长特征进行了研究。结果表明: 以胸鳍棘作为大鳍异鲦年龄鉴定材料, 鉴定结果与脊椎骨的吻合率为86.36%, 胸鳍棘是比较可靠的年龄鉴定材料。所采集样本年龄范围为1—9龄, 1—3龄为主, 占65.00%。雌雄个体生长不存在显著差异, 全长与胸鳍棘半径呈幂函数关系, L=2.0787·R_C0.6273(R2=0.8866, n=180)。各龄组实测体长均值和退算体长均值无明显差异(χ2=0.776, df=8, P=0.999)。雌雄群体实测全长与体重之间无明显差异, 拟合得体重与全长的关系式为: W=1E–4L2.4807(R2=0.8189, n=180), 其生长属异速生长类型。生长规律用von Bertalanffy方程表示, L_t=377.015·[1–e–0.0491(t+4.0195)], W_t=246.134·[1–e–0.0491(t+4.0195)]2.4807。生长拐点年龄为14.48龄, 拐点处的全长和体重分别为225.00 mm和68.40 g。大鳍异鲦个体出现小型化现象, 应合理捕捞、加强保护。     

Genetic and phenotypic correlations among feed efficiency,production and selected conformation traits in dairy cows

The difficulties and costs of measuring individual feed intake in dairy cattle are the primary factors limiting the genetic study of feed intake and utilisation, and hence the potential of their subsequent industry-wide applications. However, indirect selection based on heritable, easily measurable, and genetically correlated traits, such as conformation traits, may be an alternative approach to improve feed efficiency. The aim of this study was to estimate genetic and phenotypic correlations among feed intake, production, and feed efficiency traits (particularly residual feed intake; RFI) with routinely recorded conformation traits. A total of 496 repeated records from 260 Holstein dairy cows in different lactations (260, 159 and 77 from first, second and third lactation, respectively) were considered in this study. Individual daily feed intake and monthly BW and body condition scores of these animals were recorded from 5 to 305 days in milk within each lactation from June 2007 to July 2013. Milk yield and composition data of all animals within each lactation were retrieved, and the first lactation conformation traits for primiparous animals were extracted from databases. Individual RFI over 301 days was estimated using linear regression of total 301 days actual energy intake on a total of 301 days estimated traits of metabolic BW, milk production energy requirement, and empty BW change. Pair-wise bivariate animal models were used to estimate genetic and phenotypic parameters among the studied traits. Estimated heritabilities of total intake and production traits ranged from 0.27±0.07 for lactation actual energy intake to 0.45±0.08 for average body condition score over 301 days of the lactation period. RFI showed a moderate heritability estimate (0.20±0.03) and non-significant phenotypic and genetic correlations with lactation 3.5 % fat-corrected milk and average BW over lactation. Among the conformation traits, dairy strength, stature, rear attachment width, chest width and pin width had significant (P<0.05) moderate to strong genetic correlations with RFI. Combinations of these conformation traits could be used as RFI indicators in the dairy genetic improvement programmes to increase the accuracy of the genetic evaluation of feed intake and utilisation included in the index.     

Mosaicism, modules, and the evolution of birds: results from a Bayesian approach to the study of morphological evolution using discrete character data

The study of morphological evolution after the inferred origin of active flight homologous with that in Aves has historically been characterized by an emphasis on anatomically disjunct, mosaic patterns of change. Relatively few prior studies have used discrete morphological character data in a phylogenetic context to quantitatively investigate morphological evolution or mosaic evolution in particular. One such previously employed method, which used summed unambiguously optimized synapomorphies, has been the basis for proposing disassociated and sequential "modernizing" or "fine-tuning" of pectoral and then pelvic locomotor systems after the origin of flight ("pectoral early-pelvic late" hypothesis). We use one of the most inclusive phylogenetic data sets of basal birds to investigate properties of this method and to consider the application of a Bayesian phylogenetic approach. Bayes factor and statistical comparisons of branch length estimates were used to evaluate support for a mosaic pattern of character change and the specific pectoral early-pelvic late hypothesis. Partitions were defined a priori based on anatomical subregion (e.g., pelvic, pectoral) and were based on those hypothesized using the summed synapomorphy approach. We compare 80 models all implementing the M(k) model for morphological data but varying in the number of anatomical subregion partitions, the models for among-partition rate variation and among-character rate variation, as well as the branch length prior. Statistical analysis reveals that partitioning data by anatomical subregion, independently estimating branch lengths for partitioned data, and use of shared or per partition gamma-shaped among-character rate distribution significantly increases estimated model likelihoods. Simulation studies reveal that partitioned models where characters are randomly assigned perform significantly worse than both the observed model and the single-partition equal-rate model, suggesting that only partitioning by anatomical subregion increases model performance. The preference for models with partitions defined a priori by anatomical subregion is consistent with a disjunctive pattern of character change for the data set investigated and may have implications for parameterization of Bayesian analyses of morphological data more generally. Statistical tests of differences in estimated branch lengths from the pectoral and pelvic partitions do not support the specific pectoral early-pelvic late hypothesis proposed from the summed synapomorphy approach; however, results suggest limited support for some pectoral branch lengths being significantly longer only early at/after the origin of flight.     

Maximum activities and properties of glucose 6-phosphatase in muscles from vertebrates and invertebrates.

1. The maximum catalytic activities of glucose 6-phosphatase were measured in a large number of muscles from vertebrates and invertebrates. The activities range from less than 0.1 to 8.0 mumol/min per g fresh wt. at 30 degrees C: the highest activity, observed in the flight muscle of the wasp (Vespa vulgaris), is similar to that in rat liver. The hydrolytic activity was shown to be specific towards glucose 6-phosphate. 2. The pH optimum was 6.8 and the Km was approx. 0.6 mM (flight muscle of a moth). 3. Almost all of the glucose 6-phosphatase activity from extracts of the flight muscle of a moth and the pectoral muscle of a pigeon were recovered in the cytosolic fraction (i.e. 150,000 g supernatant). 4. During development of the locust (Schistocerca gregaria), the activity of the phosphatase in the flight muscle increased during the first 3 days after the final moult. 5. The activity of glucose 6-phosphatase from insect and avian muscle was separated from that of non-specific phosphatase on a Bio-Gel P-100 column. 6. For the activities from 63 muscles, there was a strong positive correlation between those of glucose 6-phosphatase and hexokinase, but no correlation between the activities of glucose 6-phosphatase and fructose bisphosphatase. It is suggested that the role of glucose 6-phosphate in muscle is either to produce glucose from glucose 6-phosphate derived from glycogen or to provide the enzymic basis for a substrate ("futile") cycle between glucose and glucose 6-phosphatase in muscle to improve the sensitivity of the mechanism that regulates the rate of glucose phosphorylation.