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.     

Intra-individual variation in body temperature and pectoral muscle size in nestling Alpine swifts Apus melba in response to an episode of inclement weather

The Alpine swift (Apus melba) forages on insects caught exclusively on the wing, implying that dependent nestlings face acute food shortage in periods of cold and rainy weather. Therefore, there should be strong selection on nestling swifts to evolve physiological strategies to cope with periods of undernutrition. We have investigated intra-individual changes in nestling pectoral muscle and body temperature in response to a 1-week period of inclement weather. The pectoral muscle is the largest reserves of proteins, and nestlings have to devote a large amount of energy in the maintenance of body temperature. The results show that nestling pectoral muscle size and body temperature were significantly reduced during the episode of inclement weather. Assuming that these physiological changes are adaptive, our study suggests that nestling swifts spare energy by a pronounced reduction (up to 18°C) in body temperature and use proteins from the pectoral muscle as a source of extra energy to survive prolonged periods of fasting.     

Seasonal variation in body composition in an Afrotropical passerine bird: increases in pectoral muscle mass are,unexpectedly, associated with lower thermogenic capacity

Phenotypic flexibility in avian metabolic rates and body composition have been well-studied in high-latitude species, which typically increase basal metabolic rate (BMR) and summit metabolism (M_sum) when acclimatized to winter conditions. Patterns of seasonal metabolic acclimatization are more variable in lower-latitude birds that experience milder winters, with fewer studies investigating adjustments in avian organ and muscle masses in the context of metabolic flexibility in these regions. We quantified seasonal variation (summer vs winter) in the masses of organs and muscles frequently associated with changes in BMR (gizzard, intestines and liver) and M_sum (heart and pectoral muscles), in white-browed sparrow-weavers (Plocepasser mahali). We also measured pectoral muscle thickness using a portable ultrasound system to determine whether we could non-lethally estimate muscle size. A concurrent study measured seasonal changes in BMR and M_sum in the same population of sparrow-weavers, but different individuals. There was no seasonal variation in the dry masses of the gizzard, intestines or liver of sparrow-weavers, and during the same period, BMR did not vary seasonally. We found significantly higher heart (~ 18% higher) and pectoral muscle (~ 9% higher) dry mass during winter, although ultrasound measurements did not detect seasonal changes in pectoral muscle size. Despite winter increases in pectoral muscle mass, M_sum was ~ 26% lower in winter compared to summer. To the best of our knowledge, this is the first study to report an increase in avian pectoral muscle mass but a concomitant decrease in thermogenic capacity.

     

Rainfall and habitat interact to affect the condition of a wintering migratory songbird in The Bahamas

On the subtropical and tropical wintering grounds of migratory birds, variation in moisture levels and habitat can influence the availability of food resources and subsequently impact overwintering birds. Using stable carbon isotopes in blood samples as a measure of moisture, we assessed the interactive effects of rainfall, vegetation, and moisture on the demographics and condition of Prairie Warblers (Setophaga discolor) wintering in The Bahamas. Carbon isotopes in Prairie Warbler blood were more depleted in taller, wetter habitats; we additionally detected novel temporal effects of rainfall on isotope values. During a winter with more rainfall, most birds maintained mass and pectoral muscle regardless of the habitat type occupied. In a winter with less rainfall, birds lost mass and pectoral muscle, and this effect was more pronounced in birds with enriched isotope values and birds that occupied drier, shorter habitat. Prairie Warblers exhibited strong patterns of sexual habitat segregation with males disproportionately observed in areas with taller vegetation and females in shorter vegetation. During the drier winter, older males had better maintenance of pectoral muscle compared to females and younger individuals. Also in the drier winter, daily rainfall patterns explained more of the variation in body condition compared to the date of capture; pectoral muscle was best explained by recent precipitation (during the previous 30 days), while size‐corrected mass was more a function of longer‐term (90‐day) rainfall and habitat moisture. Our findings along with other studies suggest that Prairie Warblers and other migratory birds are sensitive to interactions between annual variation in winter rainfall, within‐season daily rainfall patterns, and habitat quality. Increasing drought and habitat loss in the Caribbean may be having a negative impact on wintering bird populations. To best conserve Nearctic–Neotropical migratory passerines in the region, we recommend prioritizing the protection of the least drought‐prone wintering areas.     

Myofibrillar protein degradation in the chicken. 3-Methylhistidine release in vivo and in vitro in normal and genetically muscular-dystrophic chickens

Myofibrillar protein degradation was measured in 4-week-old normal (line 412) and genetically muscular-dystrophic (line 413) New Hampshire chickens by monitoring the rates of 3-methylhistidine excretion in vivo and in vitro. A method of perfusing breast and wing muscles was developed and the rate of 3-methylhistidine release in vitro was measured between 30 and 90min of perfusion. During this perfusion period, 3-methylhistidine release from the muscle preparation was linear, indicating that changes in 3-methylhistidine concentration of the perfusate were the result of myofibrillar protein degradation. Furthermore, the viability of the perfused muscle was maintained during this interval. After 60min of perfusion, ATP, ADP and creatine phosphate concentrations in pectoral muscle were similar to muscle freeze-clamped in vivo. Rates of glucose uptake and lactate production were constant during the perfusion. In dystrophic-muscle preparations, the rate of 3-methylhistidine release in vitro (nmol/h per g of dried muscle) was elevated 2-fold when compared with that in normal muscle. From these data the fractional degradation rates of myofibrillar protein in normal and dystrophic pectoral muscle were calculated to be 12 and 24% respectively. Daily 3-methylhistidine excretion (nmol/day per g body wt.) in vivo was elevated 1.35-fold in dystrophic chickens. Additional studies revealed that the anti-dystrophic drugs diphenylhydantoin and methylsergide, which improve righting ability of dystrophic chickens, did not alter 3-methylhistidine release in vitro. This result implies that changes in myofibrillar protein turnover are not the primary lesion in avian muscular dystrophy. From tissue amino acid analysis, the myofibrillar 3-methylhistidine content per g dry weight of muscle was similar in normal and dystrophic pectoral muscle. More than 96% of the 3-methylhistidine present in pectoral muscle was associated with the myofibrillar fraction. Dystrophic myofibrillar protein contained significantly less 3-methylhistidine (nmol/g of myofibrillar protein) than protein from normal muscle. This observation supports the hypothesis that there may be a block in the biochemical maturation and development of dystrophic muscle after hatching. Free 3-methylhistidine (nmol/g wet wt.) was elevated in dystrophic muscle, whereas blood 3-methylhistidine concentrations were similar in both lines. In summary, the increased myofibrillar protein catabolism demonstrated in dystrophic pectoral muscle correlates with the increased lysosomal cathepsin activity in this tissue as reported by others.     

Post-hatching growth and development of the pectoral and pelvic limbs in the black noddy, Anous minutus.

The black tern (Anous minutus) uses a semi-precocial growth strategy. Terrestrial locomotor capacity occurs soon after hatching, but pectoral limb development is delayed and flight is not possible until about post-hatching day 50. A growth series (hatchlings to fledglings) was used to explore how limb musculoskeletal development varied with body mass. In the pelvic limb, bone lengths scaled isometrically or with negative allometry. Gastrocnemius muscle mass and the failure load and stiffness of the tibiotarsus scaled isometrically. In the pectoral limb, pectoralis and supracoracoideus muscle masses increased with strong positive allometry that was mirrored by increases in wing bone strength and stiffness. Bending strength (sigma(ult)) and modulus (E) remained fairly constant throughout development to fledging for all limb bones. The moment of inertia (I) scaled with negative allometry for the tibiotarsus and with strong positive allometry in the wing bones. Differences in sigma(ult) and E of the tibiotarsus between pre-fledged chicks and adults was due, primarily, to increases in bone density rather than increases in the moment of inertia of the skeletal elements, whereas sigma(ult) of wing bones was a function of increases in both bone density and I. Early development of functional pelvic limbs in tree-nesting birds is relatively unusual, and presumably reflects a familial trait that does not appear to compromise breeding success in this species.     

Post-hatching growth and development of the pectoral and pelvic limbs in the black noddy, Anous minutus

The black tern (Anous minutus) uses a semi-precocial growth strategy. Terrestrial locomotor capacity occurs soon after hatching, but pectoral limb development is delayed and flight is not possible until about post-hatching day 50. A growth series (hatchlings to fledglings) was used to explore how limb musculoskeletal development varied with body mass. In the pelvic limb, bone lengths scaled isometrically or with negative allometry. Gastrocnemius muscle mass and the failure load and stiffness of the tibiotarsus scaled isometrically. In the pectoral limb, pectoralis and supracoracoideus muscle masses increased with strong positive allometry that was mirrored by increases in wing bone strength and stiffness. Bending strength (sigma(ult)) and modulus (E) remained fairly constant throughout development to fledging for all limb bones. The moment of inertia (I) scaled with negative allometry for the tibiotarsus and with strong positive allometry in the wing bones. Differences in sigma(ult) and E of the tibiotarsus between pre-fledged chicks and adults was due, primarily, to increases in bone density rather than increases in the moment of inertia of the skeletal elements, whereas sigma(ult) of wing bones was a function of increases in both bone density and I. Early development of functional pelvic limbs in tree-nesting birds is relatively unusual, and presumably reflects a familial trait that does not appear to compromise breeding success in this species.     

Evolution of a Metal-Binding Cluster in the NH2-Terminal Variable Region of Avian Fast Skeletal Muscle Troponin T: Functional Divergence on the Basis of Tolerance to Structural Drifting

This study investigated the evolution of a transition metal ion-binding cluster ([H–X–X–X–H] _n ; Tx) in the alternatively spliced NH₂-terminal variable region of avian pectoral muscle troponin T (TnT). Encoded by avian fast skeletal muscle TnT-specific P exons, Tx-like structures were expressed in the breast muscle TnT's of almost all birds examined. Their presence results in the developmentally up-regulated high molecular weight pectoral muscle TnT. Sequence analysis and metal affinity chromatography revealed that in Galliformes and Craciformes, the Tx structure evolved into multiple H–X–X–X–H pairs with a high-affinity metal-binding capacity. Turkey, chicken, quail, and curassow breast muscle TnT's contain nine, seven, four, and three consecutive or closely located metal-binding sites, respectively, in the NH₂-terminal region. The metal-binding affinity of the Tx element increased as the number of His pairs increased due to the duplication of P exons and the conversion of other exon sequences. The data show two related components of avian pectoral muscle TnT evolution: a larger, more acidic NH₂-terminal segment and a cluster of transition metal-binding sites, both of which may have functional significance for their selection value. The evolution of the Tx segment in the NH₂-terminal variable region of avian pectoral muscle TnT demonstrates a functional divergence on the basis of tolerance to structural drifting. Received: 2 May 2000 / Accepted: 5 September 2000     

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.     

3D Visualization and Measurement of Capillaries Supplying Metabolically Different Fiber Types in the Rat Extensor Digitorum Longus Muscle During Denervation and Reinnervation

The aim of this study was to determine whether capillarity in the denervated and reinnervated rat extensor digitorum longus muscle (EDL) is scaled by muscle fiber oxidative potential. We visualized capillaries adjacent to a metabolically defined fiber type and estimated capillarity of fibers with very high oxidative potential (O) vs fibers with very low oxidative potential (G). Capillaries and muscle fiber types were shown by a combined triple immunofluorescent technique and the histochemical method for NADH-tetrazolium reductase. Stacks of images were captured by a confocal microscope. Applying the Ellipse program, fibers were outlined, and the diameter, perimeter, cross-sectional area, length, surface area, and volume within the stack were calculated for both fiber types. Using the Tracer plug-in module, capillaries were traced within the three-dimensional (3D) volume, the length of capillaries adjacent to individual muscle fibers was measured, and the capillary length per fiber length (Lcap/Lfib), surface area (Lcap/Sfib), and volume (Lcap/Vfib) were calculated. Furthermore, capillaries and fibers of both types were visualized in 3D. In all experimental groups, O and G fibers significantly differed in girth, Lcap/Sfib, and Lcap/Vfib, but not in Lcap/Lfib. We conclude that capillarity in the EDL is scaled by muscle fiber size and not by muscle fiber oxidative potential. (J Histochem Cytochem 57:437–447, 2009)     

High Efficiency Perovskite‐Silicon Tandem Solar Cells: Effect of Surface Coating versus Bulk Incorporation of 2D Perovskite

Mixed‐dimensional perovskite solar cells combining 3D and 2D perovskites have recently attracted wide interest owing to improved device efficiency and stability. Yet, it remains unclear which method of combining 3D and 2D perovskites works best to obtain a mixed‐dimensional system with the advantages of both types. To address this, different strategies of combining 2D perovskites with a 3D perovskite are investigated, namely surface coating and bulk incorporation. It is found that through surface coating with different aliphatic alkylammonium bulky cations, a Ruddlesden–Popper “quasi‐2D” perovskite phase is formed on the surface of the 3D perovskite that passivates the surface defects and significantly improves the device performance. In contrast, incorporating those bulky cations into the bulk induces the formation of the pure 2D perovskite phase throughout the bulk of the 3D perovskite, which negatively affects the crystallinity and electronic structure of the 3D perovskite framework and reduces the device performance. Using the surface‐coating strategy with n‐butylammonium bromide to fabricate semitransparent perovskite cells and combining with silicon cells in four‐terminal tandem configuration, 27.7% tandem efficiency with interdigitated back contact silicon bottom cells (size‐unmatched) and 26.2% with passivated emitter with rear locally diffused silicon bottom cells is achieved in a 1 cm² size‐matched tandem.     

Explosive development of pectoral muscle fibres in large juvenile blue catfish Ictalurus furcatus

As part of an effort on scaling of pectoral spines and muscles, the basis for growth was examined in six pectoral muscles in juvenile blue catfish Ictalurus furcatus, the largest catfish in North America. Fibre number increases slowly in fish from 13·0 to 26·4 cm in total length, doubles by 27·0 cm and remains stable in larger individuals. Simultaneously, mean fibre diameter decreases by half, caused by the addition of new small fibres, before increasing non‐linearly in larger fish. The orders of magnitude disparity between the size at hatching and the size of large adults may have selected for rapid muscle fibre addition at a threshold size.     

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.     

High‐Performance Large‐Area Organic Solar Cells Enabled by Sequential Bilayer Processing via Nonhalogenated Solvents

While the performance of laboratory‐scale organic solar cells (OSCs) continues to grow over 13%, the development of high‐efficiency large area OSCs still lags. One big challenge is that the formation of bulk heterojunction morphology is an extremely complicated process and the formed morphology is also a highly delicate balance involving many parameters such as domain size, purity, miscibility, etc. The morphology control becomes much more challenging when the device area is scaled up. In this work, a highly efficient (12.9%) nonfullerene organic solar cell processed using a sequential bilayer deposition method from nonhalogenated solvents, is reported. Using this bilayer processing method, the organic solar cells can be scaled up to a larger area (1 cm²) while maintaining a high performance of 11.4% using doctor‐blade‐coating technique. Moreover, as the acceptor is hidden behind the polymer donor, the possibility of degradation by sunlight is lessened. Thus, improved photostability is observed in the bilayer structure device when compared with the bulk heterojunction device. This method offers a truly compatible processing technique for printing large‐area OSC modules.     

Diversity of dermal denticle structure in sharks: Skin surface roughness and three‐dimensional morphology

Shark skin is covered with numerous placoid scales or dermal denticles. While previous research has used scanning electron microscopy and histology to demonstrate that denticles vary both around the body of a shark and among species, no previous study has quantified three‐dimensional (3D) denticle structure and surface roughness to provide a quantitative analysis of skin surface texture. We quantified differences in denticle shape and size on the skin of three individual smooth dogfish sharks (Mustelus canis) using micro‐CT scanning, gel‐based surface profilometry, and histology. On each smooth dogfish, we imaged between 8 and 20 distinct areas on the body and fins, and obtained further comparative skin surface data from leopard, Atlantic sharpnose, shortfin mako, spiny dogfish, gulper, angel, and white sharks. We generated 3D images of individual denticles and measured denticle volume, surface area, and crown angle from the micro‐CT scans. Surface profilometry was used to quantify metrology variables such as roughness, skew, kurtosis, and the height and spacing of surface features. These measurements confirmed that denticles on different body areas of smooth dogfish varied widely in size, shape, and spacing. Denticles near the snout are smooth, paver‐like, and large relative to denticles on the body. Body denticles on smooth dogfish generally have between one and three distinct ridges, a diamond‐like surface shape, and a dorsoventral gradient in spacing and roughness. Ridges were spaced on average 56 µm apart, and had a mean height of 6.5 µm, comparable to denticles from shortfin mako sharks, and with narrower spacing and lower heights than other species measured. We observed considerable variation in denticle structure among regions on the pectoral, dorsal, and caudal fins, including a leading‐to‐trailing edge gradient in roughness for each region. Surface roughness in smooth dogfish varied around the body from 3 to 42 microns.     

Scaled‐Up Inertial Microfluidics: Retention System for Microcarrier‐Based Suspension Cultures

Recently, particle concentration and filtration using inertial microfluidics have drawn attention as an alternative to membrane and centrifugal technologies for industrial applications, where the target particle size varies between 1 µm and 500 µm. Inevitably, the bigger particle size (>50 µm) mandates scaling up the channel cross‐section or hydraulic diameter (D_H > 0.5 mm). The Dean‐coupled inertial focusing dynamics in spiral microchannels is studied broadly; however, the impacts of secondary flow on particle migration in a scaled‐up spiral channel is not fully elucidated. The mechanism of particle focusing inside scaled‐up rectangular and trapezoidal spiral channels (i.e., 5–10× bigger than conventional microchannels) with an aim to develop a continuous and clog‐free microfiltration system for bioprocessing is studied in detail. Herein, a unique focusing based on inflection point without the aid of sheath flow is reported. This new focusing mechanism, observed in the scaled‐up channels, out‐performs the conventional focusing scenarios in the previously reported trapezoidal and rectangular channels. Finally, as a proof‐of‐concept, the utility of this device is showcased for the first time as a retention system for a cell–microcarrier (MC) suspension culture.     

Identification and localization of two triad junctional foot protein isoforms in mature avian fast twitch skeletal muscle

We report evidence for two foot protein isoforms in chicken pectoral muscle. (i) Two polypeptides with molecular masses of approximately 500 kDa copurify with [3H]ryanodine binding. (ii) Both polypeptides are associated with oligomeric proteins similar in size to the mammalian skeletal muscle foot protein. (iii) The polypeptides are shown to be unique by limited proteolysis. (iv) By using isoform-specific antibodies, the polypeptides are shown to be subunits of different [3H]ryanodine-binding proteins. Using immunolabeling techniques, we have localized these proteins in chicken breast muscle by both light and electron microscopy. (v) From immunofluorescent light microscopy of longitudinal sections, it was determined that both ryanodine-binding protein isoforms exhibit identical repetitive punctate distributions near the Z-lines. (vi) In serial cross-sections both proteins have similar distributions in the same fibers. (vii) Both proteins were found to be associated with the terminal cisternae of the sarcoplasmic reticulum by immunoelectron microscopy. Based on their localization to the triadic junction, their large size and their ability to bind [3H]ryanodine, these proteins are identified as foot proteins. In conclusion, two distinct homo-oligomeric foot proteins coexist in avian fast twitch skeletal muscle. We have termed these proteins, alpha and beta foot proteins.     

Sensitivity of cultured and skinned chick myotube to calcium, strontium, and barium ions examined by recording isometric contractions.

Sensitivity of cultured chick myotubes to alkaline earth metal ions was investigated by recording contractile isometric tension through a semiconductor transducer. The myotubes were obtained by culturing myoblasts of chick embryo breast muscles, and skinned chemically before physiological experiments. Contractions developed in response to Ca2+ in a bathing medium higher than 3 x 10(-7) M and reached maximum at 1 x 10(-5) M. Sr2+ was less effective than Ca2+; the threshold concentration was 1 x 10(-5) M and the tension reached maximum at 1 x 10(-3) M. Ba2+ was the least effective among the three alkaline earth metal ions; only one fifth of the Ca(2+)-induced maximum tension was attained at 1 x 10(-3) M. The sensitivity was similar to that of the mature pectoral muscle fiber, a fast twitch muscle fiber, rather than that of the anterior latissimus dorsi, a slow tonic muscle fiber. The sensitivity was shown to be dependent on its troponin C by replacing it with troponin C from the mature pectoral or cardiac muscle. This indicates that TnC of a fast-muscle type is expressed in the cultured chick myotube as in the mature pectoral muscle. The contractile apparatus was thus shown to be well developed in the cultured myotube with characteristics similar to the mature fast twitch muscle fiber.     

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.     

Chimeras vs X inactivation mosaics: significance of differences in pigment distribution

Cell cultures of cardiac, pectoral, and thigh muscle of chick embryos synthesized myoglobin, as measured by incorporation of radioactive lysine detected by radioimmunoprecipitation. Liver and skin cultures, although active in protein synthesis, failed to demonstrate myoglobin synthesis. Puromycin inhibited myoglobin synthesis by the cell cultures. The electrophoretic characteristics of the myoglobin antigen synthesized by thigh and pectoral muscle were identical. Myglobin synthesizing progenitor cells attached to plastic dishes in 1 hr, but not completely in 0.5 hr. Cells, unattached at 0.5 hr, were enriched in myoglobin synthesizing cells. Incorporation of lysine-U-¹⁴C into myoglobin was maximal in confluent cultures and its increase paralleled the increase of cell fusion in the cultures. The ability of pectoral, white muscle to synthesize myoglobin in a manner equivalent to that of cardiac tissue was unexpected because of its failure to synthesize myoglobin in vivo and may indicate that factors in the whole organism may regulate the expression of this muscle cell's capabilities.