Development of the mitochondrial apparatus and blood supply of skeletal muscle fibers during ontogenesis of domestic fowl

The diameter, length, and numerical density of capillaries, diameter of muscle fibers, size and numerical density of mitochondrial profiles, and relative volume of mitochondria in them were determined in the chicken red oxidative gastrocnemius and white glycolytic pectoral muscle during development from day 10 of embryogenesis to six month of postnatal life. The bulk blood flow was measured in these muscles by hydrogen clearance during postembryonic development. During embryogenesis, the fibers of gastrocnemius muscle develop and grow at a higher rate, while during postembryonic development, those of the pectoral muscle develop faster. The density of mitochondrial profiles increases during embryogenesis and decreases after hatching, while their mean size increases, especially in the oxidative fibers, but it somewhat decreases in 6-month old chicks. Redistribution of mitochondria across the fiber section during development takes place in both muscles: they are localized predominantly in the center in 18-day embryos and in the periphery, especially in the gastrocnemius fibers, in 6-month old chicks. At hatching, the length of capillaries is similar in both muscles, but as chicks grow, the proportion of longer (more than 600 µm) capillaries in the pectoral muscle sharply increases, while their density and bulk blood flow decrease. Ratios were determined between structural parameters of the capillary bed and mitochondria, on the one hand, and oxygen consumption (ml/min per 1 mm fiber and 100 g muscle mass), on the other.__________Translated from Ontogenez, Vol. 36, No. 2, 2005, pp. 135–144.Original Russian Text Copyright © 2005 by Belichenko, Korostyshevskaya, Maksimov, Shoshenko.     

Allometric dependences of oxygen transport parameters in skeletal muscles during ontogenesis of domestic fowl

In domestic fowl, from day 10 of embryogenesis to six month of postnatal life, investigation into the white glycolytic pectoral and red oxidative gastrocnemius muscles allometric dependences of the structural and functional parameters providing muscular fibres by oxygen: speed of breath of an isolated muscular fibre, size of a surface of an external membrane of mitochondria in a fibre, its permeability to oxygen, density of the capillaries located around of a fibre and in all muscle, volumetric speed of a muscular blood flow, and connection of speed of breath of muscular fibres with weight of a body of a bird.     

Muscle capillarity in chicks following hypoxia

1. Muscle capillarity was examined in chicks exposed to normobaric hypoxia with and without increased workload. 2. Capillarity was higher in the lateral head of the gastrocnemius, but not in the other muscles examined. Increased workload did not contribute to the effects of hypoxia. 3. Thus, hypoxia served as a stimulus for the development of new capillaries in muscle containing twitch fibers, but not in muscle containing tonic fibers.     

Stimulation with monochromatic green light during incubation alters satellite cell mitotic activity and gene expression in relation to embryonic and posthatch muscle growth of broiler chickens

Previous studies showed that monochromatic green light stimuli during embryogenesis accelerated posthatch body weight (BW) and pectoral muscle growth of broilers. In this experiment, we further investigated the morphological and molecular basis of this phenomenon. Fertile broiler eggs (Arbor Acres, n=880) were pre-weighed and randomly assigned to 1 of the 2 incubation treatment groups: (1) dark condition (control group), and (2) monochromatic green light group (560 nm). The monochromatic lighting systems sourced from light-emitting diode lamps and were equalized at the intensity of 15 lx at eggshell level. The dark condition was set as a commercial control from day 1 until hatching. After hatch, 120 male 1-day-old chicks from each group were housed under incandescent white light with an intensity of 30 lx at bird-head level. No effects of light stimuli during embryogenesis on hatching time, hatchability, hatching weight and bird mortality during the feeding trial period were observed in the present study. Compared with the dark condition, the BW, pectoral muscle weight and myofiber cross-sectional areas were significantly greater on 7-day-old chicks incubated under green light. Green light also increased the satellite cell mitotic activity of pectoral muscle on 1- and 3-day-old birds. In addition, green light upregulated MyoD, myogenin and myostatin mRNA expression in late embryos and/ or newly hatched chicks. These data suggest that stimulation with monochromatic green light during incubation promote muscle growth by enhancing proliferation and differentiation of satellite cells in late embryonic and newly hatched stages. Higher expression of myostatin may ultimately help prevent excessive proliferation and differentiation of satellite cells in birds incubated under green light.     

Catabolic capacity of the muscles of shorebird chicks: maturation of function in relation to body size

Newly hatched precocial chicks of arctic shorebirds are able to walk and regulate their body temperatures to a limited extent. Yet, they must also grow rapidly to achieve independence before the end of the short arctic growing season. A rapid growth rate may conflict with development of mature function, and because of the allometric scaling of thermal relationships, this trade-off might be resolved differently in large and small species. We assessed growth (mass) and functional maturity (catabolic enzyme activity) in leg and pectoral muscles of chicks aged 1-16 d and adults of two scolopacid shorebirds, the smaller dunlin (Calidris alpina: neonate mass 8 g, adult mass 50 g) and larger whimbrel (Numenius phaeopus; neonate mass 34 g, adult mass 380 g). Enzyme activity indicates maximum catabolic capacity, which is one aspect of the development of functional maturity of muscle. The growth rate-maturity hypothesis predicts that the development of catabolic capacity should be delayed in faster-growing muscle masses. Leg muscles of both species were a larger proportion of adult size at hatching and grew faster than pectoral muscles. Pectoral muscles grew more rapidly in the dunlin than in the whimbrel, whereas leg muscles grew more rapidly in the whimbrel. In both species and in both leg and pectoral muscles, enzyme activities generally increased with age, suggesting increasing functional maturity. Levels of citrate synthase activity were similar to those reported for other species, but l-3-hydroxyacyl-CoA-dehydrogenase and pyruvate kinase (PK) activities were comparatively high. Catabolic capacities of leg muscles were initially high compared to those of pectoral muscles, but with the exception of glycolytic (PK) capacities, these subsequently increased only modestly or even decreased as chicks grew. The earlier functional maturity of the more rapidly growing leg muscles, as well as the generally higher functional maturity in muscles of the more rapidly growing dunlin chicks, contradicts the growth rate-maturity function trade-off and suggests that birds have considerable latitude to modify this relationship. Whimbrel chicks, apparently, can rely on allometric scaling of power requirements for locomotion and the thermal inertia of their larger mass to reduce demands on their muscles, whereas dunlin chicks require muscles with higher metabolic capacity from an earlier age. Thus, larger and smaller species may adopt different strategies of growth and tissue maturation.     

Ontogeny of catabolic and morphological properties of skeletal muscle of the red-winged blackbird (Agelaius phoeniceus)

Thermogenic capabilities of red-winged blackbirds improve markedly during their 10-12-day nestling period, especially between day 5 and day 8. The time course of improvements may be determined by the maturation of skeletal muscles involved in shivering thermogenesis, particularly the pectoralis muscles. To test this hypothesis, morphological and biochemical changes in pectoral and leg muscles were measured in young and adult blackbirds. Both muscles grew disproportionately relative to body mass. The pectoralis consisted entirely of fast-twitch fibers, predominantly fast oxidative glycolytic. In contrast, the gastrocnemius muscle consisted of a mixture of slow and fast fibers (predominantly fast glycolytic). Although fiber composition was constant, both cross-sectional area and density of fibers increased with age in both muscles. Catabolic capacities of the pectoralis increased significantly (approximately 7-8-fold) throughout the nestling period, most abruptly after day 3 (citrate synthase, CS) or day 4 (3-hydroxacyl-CoA-dehydrogenase, HOAD). Myofibrillar ATPase activities in the pectoralis were initially low, but increased after day 5. Further increases in CS and myofibrillar ATPase activities occurred in the pectoralis after fledging. CS and HOAD activities in the leg were much lower, but myofibrillar ATPase activities were remarkably similar in the two muscles, differing only in adults. These results are consistent with the hypothesis that the development of endothermy is dependent on the morphological and biochemical maturation of skeletal muscles important in thermogenesis.     

Muscle development in larvae of a fast growing tropical freshwater fish, the curimatã-pacú

The distribution and ultrastructure of myotomal muscle fibres was studied in larvae and early juveniles of the curimatã-pacú Prochilodus marggravii , a tropical freshwater fish endemic to the São Francisco River system, Brazil. At 26°C, larvae hatched 15 h post-fertilization at a relatively early stage of development with the head still curved around the yolk-sac (head-trunk angle greater than 45°), and prior to pigmentation of the eyes and formation of the jaws, gut and pectoral fins. Although motile the swimming muscles of newly-hatched larvae were largely undifferentiated. The myotomes were made up of a single layer of superficial muscle fibres containing six to eight myofibrils and abundant mitochondria, surrounding an inner core of myoblasts, myotubes and immature muscle fibres. The volume densities of mitochondria and myofibrils in the immature inner muscle fibres of 1-day-old lavae were 14.5 and 6.4% respectively. The body axis straightened within 24 h of hatching and the yolk sac was completely absorbed by 72 h. Larval development was rapid with gill filaments, a muscular stomach, liver and swimbladder present after 7 days. The inner muscle fibres were well differentiated in 7-day-old larvae; the volume density of myofibrils had increased to 63.1% whereas the volume density of mitochondria had decreased to 3.5%. In 14-day-old juveniles the superficial muscle had thickened to a layer two to three fibres thick in the region of the lateral line nerve and capillaries were present in the inner muscle. Muscle growth until 14 days was largely due to the hypertrophy of the fibres present at hatching.     

Blood flow in skeletal muscles of chicken in the embryonic and early postembryonic periods

In chicken Leghorn, blood flow volume speed in pectoralis and gastrocnemius muscles was measured on 15 and 19 day-old embryos and at the 1st and the 10th days alter hatching. It was revealed that in the last quarter of embryogenesis BF in muscles did not vary remaining in both muscles in identical limits. Similar BF parameters in pectoralis and gastrocnemius muscles and their age-dependent dynamics were observed at embryos with the detained development (with the body weight 2-fold less than the norm). After hatching, the blood flow in both muscles was grown, on the average, 2.4-fold and remained high by the 10th day, a little decreasing in the pectoralis muscle. It was shown, that increase of a muscular blood flow after hatching was accompanied by different changes of anatomic lumen of the arteries addressed in pectoralis and gastrocnemius muscles: in the former it decreased, in the latter--increased.     

Expression of uncoupling protein-3 in subsarcolemmal and intermyofibrillar mitochondria of various mouse muscle types and its modulation by fasting.

Uncoupling protein-3 (UCP3) is a mitochondrial inner-membrane protein abundantly expressed in rodent and human skeletal muscle which may be involved in energy dissipation. Many studies have been performed on the metabolic regulation of UCP3 mRNA level, but little is known about UCP3 expression at the protein level. Two populations of mitochondria have been described in skeletal muscle, subsarcolemmal (SS) and intermyofibrillar (IMF), which differ in their intracellular localization and possibly also their metabolic role. To examine if UCP3 is differentially expressed in these two populations and in different mouse muscle types, we developed a new protocol for isolation of SS and IMF mitochondria and carefully validated a new UCP3 antibody. The data show that the density of UCP3 is higher in the mitochondria of glycolytic muscles (tibialis anterior and gastrocnemius) than in those of oxidative muscle (soleus). They also show that SS mitochondria contain more UCP3 per mg of protein than IMF mitochondria. Taken together, these results suggest that oxidative muscle and the mitochondria most closely associated with myofibrils are most efficient at producing ATP. We then determined the effect of a 24-h fast, which greatly increases UCP3 mRNA (16.4-fold) in muscle, on UCP3 protein expression in gastrocnemius mitochondria. We found that fasting moderately increases (1.5-fold) or does not change UCP3 protein in gastrocnemius SS or IMF mitochondria, respectively. These results show that modulation of UCP3 expression at the mRNA level does not necessarily result in similar changes at the protein level and indicate that UCP3 density in SS and IMF mitochondria can be differently affected by metabolic changes.     

Patterns of muscle activity during different behaviors in chicks: implications for neural control

The large behavioral repertoire that spans the embryonic and postembryonic stages of development make chicks an ideal system for identifying patterns of muscle activity that are common to different behaviors and those that are behavior-specific. The main goal of this work was to identify the similar and dissimilar aspects of the recruitment patterns and the regulation of muscle activity during three distinct postembryonic behaviors: walking, swimming and airstepping. We identified two synergies that were common to each of these behaviors. The synergies were not disrupted by the absence of FT1 activity in airstepping. Within each synergy the recruitment time, recruitment order and duration of activity were not rigid, but varied according to the context-specific resistance that the leg encountered. Unlike the other muscles, FT2 activity was not recruited as part of the same synergy in each behavior. When weight-bearing contact with the substrate did not occur, as in swimming and airstepping, as well as in walking in chicks with deafferented legs, FT2 activity was not recruited as part of either synergy, but was recruited during the time between them. Although not identical, embryonic motility and hatching motor pattern both show the two synergies described for the postembryonic behaviors. Like the latter behaviors, the synergies tolerated the absence of activity from specific muscles. Thus, we suggest that the CNS produces different behaviors using many of the same muscles by organizing the patterned activity around two common synergies while permitting the different muscles that participate in a synergy to be modified in tandem or on an individual basis. Furthermore, the common synergies are established early during prenatal development in chicks.Abbreviations aIF anterior iliofibularius - CF caudilioflexorius - CNS central nervous system - EMG electromyogram - FT femorotibialis - GL gastrocnemius lateralis - P1 protraction 1 - P2 protraction 2 - pIF posterior iliofibularis - R retraction - SA sartorius - TA tibialis anterior - pIF posterior iliofibularis - ms millisecond     

Capillarity and diffusion distances in skeletal muscles in birds

Summary Tissue capillarity and diffusion distances were determined for red and white skeletal muscles of adult birds ranging in mass from 10.8 to 6200 g. In addition, literature values for capillarity and diffusion distances in skeletal muscles of mammals were incorporated into the data set. Muscle mass was closely coupled to body mass. However, no significant allometric relations were found for any of the other variables measured. Number of capillaries per fiber was not correlated with cross sectional area of individual muscle fibers. Thus, capillary density decreased in a hyperbolic manner against fiber area and diffusion distance decreased in a hyperbolic manner against the number of capillaries per muscle fiber. Red muscles had significantly higher numbers of capillaries per fiber and significantly shorter diffusion distances than did white muscles. The patterns for tissue capillarity and diffusion distances in avian muscle reported here are similar to values reported previously for mammalian muscles. In both taxanomic groups capillarity and diffusion distances are independent of body mass. In addition, diffusion distances are characteristic of capillaries distributed in random arrays through the muscle cross section.Abbreviations ALD muscle anterior latissimus dorsi - CD numerical density of capillaries in muscle cross section - C/F number of capillaries per individual muscle fiber - FCSA fiber cross sectional area - GST muscle gastrocnemius - LGST lateral head of muscle gastrocnemius - MGST medial head of muscle gastrocnemius - MM muscle mass - PLD muscle posterior latissimus dorsi     

INVERSE RELATIONSHIP BETWEEN FUNCTIONAL MATURITY AND EXPONENTIAL GROWTH RATE OF AVIAN SKELETAL MUSCLE: A CONSTRAINT ON EVOLUTIONARY RESPONSE

In this study, we investigate whether a tissue-level constraint can explain the general inverse relationship between growth rate and precocity of development in birds. On the whole, altricial (dependent) chicks grow three to four times faster than the less dependent, more able chicks of precocial species of similar adult mass. We suggest that an antagonism between growth and acquisition of mature function in skeletal muscle constrains postnatal growth and development in most species of birds. Altricial species, represented by European starlings in this study, hatch with skeletal muscle having low capacity for generating force but grow rapidly. Conversely, precocial species (northern bobwhite quail and Japanese quail), hatch with relatively mature skeletal muscle, especially in their legs, but grow more slowly. As development proceeds in all species, exponential growth rates decrease as muscles acquire adult levels of function. Among four variables associated with muscle function, exponential growth rate (EGR) was negatively correlated with pyruvate kinase activity (glycolysis), potassium concentration (electrical potential), and dry weight fraction (contractile proteins) in both pectoral and leg muscles but not with citrate synthase activity (aerobic metabolism) in either set of muscles. For pectoral muscle, these variables accounted for 87% of the total variation in EGR in all three species combined despite a twofold difference in growth rates between the starling and quail. EGRs of leg muscle (51% of variation accounted for) were less than predicted by the pectoral-muscle equation in quail during the early part of the postnatal period and in starlings during the late postnatal period. This result would not contradict a growth rate/maturity constraint hypothesis if EGRs were down-regulated for allometric or other considerations.     

Skeletal muscle fiber composition of the English sparrow (Passer domesticus)

Substrate utilization by English sparrow skeletal muscle has been extensively studied in our lab. However, there are few published studies on the muscle fiber composition of English sparrow wing and gastrocnemius muscles. The objective of the present study was to examine the fiber type composition of a variety of muscles in the English sparrow. The classification of a muscle fiber as fast glycolytic, slow oxidative, or fast oxidative glycolytic provides insight into the physiological function of muscles. Therefore, we completed mATPase and NADH stains on four muscles of the sparrow wing, as well as the gastrocnemius muscle, to characterize these muscle fiber types. Results show that the fibers of extensor digitorum communis, extensor metacarpi ulnaris, and extensor metacarpi radialis are homogeneous fast oxidative. The fibers of the supinator are homogeneous fast oxidative in 62.5% of samples, and heterogeneous (45.2% fast oxidative, 54.8% fast nonoxidative) in 37.5% of samples. Whereas the gastrocnemius muscle fibers are heterogeneous (10% fast oxidative, 64% fast nonoxidative, 26% slow oxidative) in all muscles examined.     

The distribution of capillaries in the somatic musculature of two vertebrate types with particular reference to teleost fish

The distribution of capillaries in teleost and rat striated muscles was investigated using a number of different methods. A new method for directly viewing capillaries was developed. Teleost white muscle has a capillary: fibre (C:F) ratio of between 0.2 and 0.3; and 0.6 to 1.0 peripheral capillaries per muscle fibre. 26-49% of fibres had no peripheral capillaries. Values for the rat gastrocnemius were 1.2, 2.6 and 4.8% respectively which compares well with literature values. Flathead red muscle had a C:F ratio of between 1.9 and 2.5; and between 5.3 and 6.6 peripheral capillaries per muscle fibre depending on the method used. Values for rat soleus were 1.8 and 4.1 respectively. Teleost pink fibres had an intermediate number of capillaries. Rat striated muscle, particularly the gastrocnemius, was found to be heterogeneous with respect to the distribution of capillaries. Flathead red muscle was homogeneous whilst teleost white muscle was only slightly variable. Flathead red muscle fibres are well suppled with subsarcolemmal mitochondria. These show a clumped distribution corresponding to the position of capillaries. In contrast teleost white fibres are almost totally devoid of these and all other mitochondria. No differences were observed in the vascularisation of either muscle type along the length of the fish. The results are discussed in relation to the division of labour between fibre types during swimming.     

Diversity of fast myosin heavy chain expression during development of gastrocnemius, bicep brachii, and posterior latissimus dorsi muscles in normal and dystrophic chickens

The expression of fast myosin heavy chain (MHC) isoforms was examined in developing bicep brachii, lateral gastrocnemius, and posterior latissimus dorsi (PLD) muscles of inbred normal White Leghorn chickens (Line 03) and genetically related inbred dystrophic White Leghorn chickens (Line 433). Utilizing a highly characterized monoclonal antibody library we employed ELISA, Western blot, immunocytochemical, and MHC epitope mapping techniques to determine which MHCs were present in the fibers of these muscles at different stages of development. The developmental pattern of MHC expression in the normal bicep brachii was uniform with all fibers initially accumulating embryonic MHC similar to that of the pectoralis muscle. At hatching the neonatal isoform was expressed in all fibers; however, unlike in the pectoralis muscle the embryonic MHC isoform did not disappear. With increasing age the neonatal MHC was repressed leaving the embryonic MHC as the only detectable isoform present in the adult bicep brachii muscle. While initially expressing embryonic MHC in ovo, the post-hatch normal gastrocnemius expressed both embryonic and neonatal MHCs. However, unlike the bicep brachii muscle, this pattern of expression continued in the adult muscle. The adult normal gastrocnemius stained heterogeneously with anti-embryonic and anti-neonatal antibodies indicating that mature fibers could contain either isoform or both. Neither the bicep brachii muscle nor the lateral gastrocnemius muscle reacted with the adult specific antibody at any stage of development. In the developing posterior latissimus dorsi muscle (PLD), embryonic, neonatal, and adult isoforms sequentially appeared; however, expression of the embryonic isoform continued throughout development. In the adult PLD, both embryonic and adult MHCs were expressed, with most fibers expressing both isoforms. In dystrophic neonates and adults virtually all fibers of the bicep brachii, gastrocnemius, and PLD muscles were identical and contained embryonic and neonatal MHCs. These results corroborate previous observations that there are alternative programs of fast MHC expression to that found in the pectoralis muscle of the chicken (M.T. Crow and F.E. Stockdale, 1986, Dev. Biol. 118, 333-342), and that diversification into fibers containing specific MHCs fails to occur in the fast muscle fibers of the dystrophic chicken. These results are consistent with the hypothesis that avian muscular dystrophy is a developmental disorder that is associated with alterations in isoform switching during muscle maturation.     

Embryonic muscle development of Convoluta pulchra (Turbellaria-acoelomorpha, platyhelminthes)

We studied the embryonic development of body-wall musculature in the acoel turbellarian Convoluta pulchra by fluorescence microscopy using phalloidin-bound stains for F-actin. During stage 1, which we define as development prior to 50% of the time between egg-laying and hatching, actin was visible only in zonulae adhaerentes of epidermal cells. Subsequent development of muscle occurred in two distinct phases: first, formation of an orthogonal grid of early muscles and, second, differentiation of other myoblasts upon this grid. The first elements of the primary orthogonal muscle grid appeared as short, isolated, circular muscle fibers (stage 2; 50% developmental time), which eventually elongated to completely encircle the embryo (stage 3; at 60% of total developmental time). The first primary longitudinal fibers appeared later, along with some new primary circular fibers, by 60-63% of total developmental time (stage 4). From 65 to 100% of total developmental time (stages 5 to 7), secondary fibers, using primary fibers as templates, arose; the number of circular and longitudinal muscles thus increased, and at the same time parenchymal muscles began appearing. Hatchlings (stage 8) possessed about 25 circular and 30 longitudinal muscles as well as strong parenchymal muscles. The remarkable feature of the body wall of many adult acoel flatworms is that longitudinal muscles bend medially and cross each other behind the level of the mouth. We found that this development starts shortly after the appearance of the ventral mouth opening within the body wall muscle grid. The adult organization of the body-wall musculature consists of a grid of several hundred longitudinal and circular fibers and a few diagonal muscles. Musculature of the reproductive organs developed after hatching. Thus, extensive myogenesis must occur also during postembryonic development. Comparison between the turbellarians and the annelids suggests that formation of a primary orthogonal muscle grid and its subsequent use as a template for myoblast differentiation are the two basic developmental phases in vermiform Spiralia if not in the Bilateria as a whole. Finally, our new data suggest that for the Acoela the orthogonal primary patterning of longitudinal and circular muscles in the body wall is achieved without using originally positional information of the nervous system.     

Differential expression of the Ca2+-binding protein parvalbumin during myogenesis in Xenopus laevis

We have used immunocytological techniques to examine the developmental expression of the Ca2+-binding protein parvalbumin in Xenopus laevis embryos. Western blot experiments show that at least three different forms of parvalbumin are expressed during embryogenesis; the tadpole tail expresses one form, adult brain expresses another, mylohyoid muscle expresses both, and gastrocnemius and sartorius muscles express these two plus a third form. Parvalbumin (PV) is first detectable by immunofluorescence at stages 24-25 of development, a time when myotomal muscles are differentiating and contractile activity occurs spontaneously in embryos. At metamorphosis, PV is expressed in developing limb muscles. While the majority of skeletal muscle fibers express high levels of PV in both embryos and adults, a second fiber type has no detectable PV. The arrangement of PV-containing fibers is stereotyped in each muscle group examined. Histochemical staining of tadpole muscles indicate that PV-containing fibers correspond to fast-twitch skeletal muscles, whereas those without PV correspond to slow-twitch muscles. During tail resorption at metamorphosis, PV appears to be extruded from dying tail muscle cells and taken up by phagocytic cells.     

Liver- and muscle amino-acid concentrations during the development of domestic fowl

The concentrations of free amino acids in liver, leg muscle and wing muscle of developing domestic fowl chicks were measured and compared with those of adults. Leg and breast muscles showed a remarkably parallel pattern of change in free-amino-acid concentrations during development up to day 5 after hatching, in agreement with their lack of differentiation up to day 5. Liver free-amino-acid concentration pattern with the development were very similar to those of the muscles, in significant difference with Mammals. Adult free tissue amino acids were lower than those of developing chicks. Most changes in amino-acid concentration in chick tissues were observed around hatching, and have been tentatively attributed to changes in diet. Combined amino acids changed very little during the period studied in muscles and liver. Taurine constituted a very big share of total amino acids.     

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.