The evolution of hindlimb tendons and muscles on the line to crown-group birds

The anatomy and functions of muscle-tendon complexes and their bony attachments in birds and their outgroups show how the major pelvic limb muscle groups evolved. Fossils reveal that most changes evolved after the divergence of archosaurs in the Triassic, particularly in the dinosaurian precursors to birds. Three-dimensional limb control became concentrated at the hip joint; more distal joints and muscles were restricted to flexion or extension early in dinosaur evolution. Hip extensors expanded even though the primary femoral retractor M. caudofemoralis longus was reduced. Hip flexors and two-joint "hamstring" muscles were simplified to a few large heads. Knee extensors increased their sizes and moment arms early in bipedal dinosaurs, but the patella and cranial cnemial crest evolved later in birds. Lower limb muscles expanded as ossifications such as the hypotarsus increased their moment arms. The ossification of lower limb tendons, particularly in extensors, is a recent novelty of birds. Muscles and tendons that develop large forces, stresses, and moments to stabilize or move the limbs became increasingly prominent on the line to birds. Locomotion evolved in a stepwise pattern that only recently produced the derived limb control mechanisms of crown-group birds, such as the strongly flexed hip and knee joints.     

The integrated function of muscles and tendons during locomotion

The mechanical roles of tendon and muscle contractile elements during locomotion are often considered independently, but functionally they are tightly integrated. Tendons can enhance muscle performance for a wide range of locomotor activities because muscle-tendon units shorten and lengthen at velocities that would be mechanically unfavorable for muscle fibers functioning alone. During activities that require little net mechanical power output, such as steady-speed running, tendons reduce muscular work by storing and recovering cyclic changes in the mechanical energy of the body. Tendon stretch and recoil not only reduces muscular work, but also allows muscle fibers to operate nearly isometrically, where, due to the force-velocity relation, skeletal muscle fibers develop high forces. Elastic energy storage and recovery in tendons may also provide a key mechanism to enable individual muscles to alter their mechanical function, from isometric force-producers during steady speed running to actively shortening power-producers during high-power activities like acceleration or uphill running. Evidence from studies of muscle contraction and limb dynamics in turkeys suggests that during running accelerations work is transferred directly from muscle to tendon as tendon stretch early in the step is powered by muscle shortening. The energy stored in the tendon is later released to help power the increase in energy of the body. These tendon length changes redistribute muscle power, enabling contractile elements to shorten at relatively constant velocities and power outputs, independent of the pattern of flexion/extension at a joint. Tendon elastic energy storage and recovery extends the functional range of muscles by uncoupling the pattern of muscle fiber shortening from the pattern of movement of the body.     

Orientation of tendons in vivo with active and passive knee muscles

Tendon orientations in knee models are often taken from cadaver studies. The aim of this study was to investigate the effect of muscle activation on tendon orientation in vivo. Magnetic resonance imaging (MRI) images of the knee were made during relaxation and isometric knee extensions and flexions with 0 degrees , 15 degrees and 30 degrees of knee joint flexion. For six tendons, the orientation angles in sagittal and frontal plane were calculated. In the sagittal plane, muscle activation pulled the patellar tendon to a more vertical orientation and the semitendinosus and sartorius tendons to a more posterior orientation. In the frontal plane, the semitendinosus had a less lateral orientation, the biceps femoris a more medial orientation and the patellar tendon less medial orientation in loaded compared to unloaded conditions. The knee joint angle also influenced the tendon orientations. In the sagittal plane, the patellar tendon had a more anterior orientation near full extension and the biceps femoris had an anterior orientation with 0 degrees and 15 degrees flexions and neutral with 30 degrees flexions. Within 0 degrees to 30 degrees of flexion, the biceps femoris cannot produce a posterior shear force and the anterior angle of the patellar tendon is always larger than the hamstring tendons. Therefore, co-contraction of the hamstring and quadriceps is unlikely to reduce anterior shear forces in knee angles up to 30 degrees . Finally, inter-individual variation in tendon angles was large. This suggests that the amount of shear force produced and the potential to counteract shear forces by co-contraction is subject-specific.     

Geographic range size and evolutionary age in birds

Together with patterns of speciation and extinction, post-speciation transformations in the range sizes of individual species determine the form of contemporary species range-size distributions. However, the methodological problems associated with tracking the dynamics of a species' range size over evolutionary time have precluded direct study of such range-size transformations, although indirect evidence has led to several models being proposed describing the form that they might take. Here, we use independently derived molecular data to estimate ages of species in six monophyletic groups of birds, and examine the relationship between species age and global geographic range size. We present strong evidence that avian range sizes are not static over evolutionary time. In addition, it seems that, with the regular exception of certain taxa (for example island endemics and some threatened species), range-size transformations are non-random in birds. In general, range sizes appear to expand relatively rapidly post speciation; subsequently; and perhaps more gradually, they then decline as species age. We discuss these results with reference to the various models of range-size dynamics that have been proposed.     

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     

Fibrous framework of human skeletal muscles, fasciae and tendons

By means of scanning and transmissive electron microscopy, the construction of the fibrous framework of the human skeletal muscles, fasciae and tendons has been investigated and its morphofunctional analysis has been performed. The fibrous framework of the endomysium is presented as a complexly organized system of anastomosing fibers of the connective tissue, forming a net-like construction. The fibrous structures of the framework are united into a whole construction by connecting fibers and fibrils. Different types of structural interconnection of collagenous fibers with sarcolemma are revealed. The structure of the fibrous framework both in different muscles and within one muscle has certain peculiarities. The main constructive element of the fascial fibrous framework make large anastomosing collagenous fibers, their architectonics is stabilized by connective fibers and fibrils. The construction of the tendinous fibrous framework is characterized by a pronounced anisotropia of the largest collagenous fibers and a developed network of connective structures both on the surface and inside the collagenous fibers. Structural mechanisms, interconnecting muscles and tendons, are demonstrated. Presence of anastomoses between the fibrils in the composition of the collagenous fibers in the fascia and Achilles tendon are stated. Together with the peculiarities existing, the general principle of the structural organization of the fibrous framework of the muscle system is the net-like constructure dependent on presence of anastomoses and elements of the connective system between the fibrous structures. Depending on the organ's function, the construction of the network acquires certain specific morphological forms.     

Allometry of the leg muscles of birds

The musculoskeletal components of the hindlimbs of 20 species of birds, considered non-runners, were examined. Allometry was used to compare these data with previously published information on the limbs of running birds. In non-runners the digital flexor muscle and tendon areas scaled approximately isometrically, in contrast to running birds where tendon areas had a lower exponent. Non-running birds had muscle fibre areas approximately half that of runners of equal mass. In both groups, the muscle:tendon area ratio for m. gastrocnemius increased as M^0.13, suggesting factors other than elastic energy storage are important. Runners exhibited relatively longer tibiotarsi and tarsometatarsi and shorter toes. With very few exceptions, the linear dimensions of bones, tendon cross-sectional areas, and muscle masses and fibre areas in the legs of the non-running birds scaled closely according to the requirements for geometric similarity, but the confidence limits are often wide. Deviations from geometric similarity in birds reflect differences in locomotor behaviours and abilities.     

Interrelationships between egg mass and adult body mass and metabolism among passerine birds

Summary The regression of egg mass of Passeriformes against female body mass (n=1244) and basal metabolic rate of Passeriformes against body mass (n=159) have similar slopes, indicating that for this group egg mass is directly proportional to basal metabolic rate and that the relative egg mass (% of body mass) is directly proportional to the weight-specific metabolism. This relationship and the average caloric density of passerine eggs (n=38) provides an estimate of the cost of egg production, which for single eggs is 41 % of the basal metabolic rate.

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Beziehungen zwischen Eigewicht, Körpergewicht und Stoffwechsel bei Sperlingsvögeln

Zusammenfassung Die Regressionsgeraden von Eigewichten der Passeriformes und weiblicher Körpergewichte (N=1244) einerseits sowie von Ruheumsatz und Körpergewichten (N=159) andererseits haben vergleichbare Steigungen. Das bedeutet, (1) daß für diese Vogelordnung das Eigewicht proportional zum Ruheumsatz und (2) daß das relative Eigewicht (% des Körpergewichtes) proportional zum gewichtspezifischen Stoffwechsel ist. Dieses Verhältnis und der durchschnittliche kalorische Wert der Eier (N=38) erlauben die Kosten der Eiproduktion zu schätzen: sie betragen für das einzelne Ei 41 % des Ruheumsatzes.

     

Origin of cutaneous smooth muscles in birds (author's transl)

The origin of smooth muscles in the skin of bird embryos has been analyzed in heterospecific quail/chick recombinants. The somitic mesoderm of the wing level of 2-day chick embryos was replaced by homotopic or heterotopic somitic mesoderm from quail embryos. The cellular constitution of tissues was observed in twelve recombinant embryos at 17 or 18 days of incubation. Results show that feather smooth muscles and vascular smooth muscles have the same origin as the cutaneous mesenchyme in which they differentiate. They are of somatopleural origin in the wing integument and of somitic (dermatomal) origin in the dorsal integument. This study further reveals that the muscular and connective tissue wall of blood vessels does not have the same embryonic origin as the endothelium. It is suggested that the latter originates from the primitive aorta.     

Geographical range as predictor of spatial expansion of invading birds

Many studies have been carried out on predictive traits, such as geographical range, but most of them were related to introduced species and considered the invasion as a whole. The contrasting results previously obtained suggest that studies should take into account the dynamics of the invasion process (immigration, establishment, spread). We hypothesise that the geographical range reflects the species tolerance to new environments, and is related especially to the establishment and spread of the invasion process. First, data on spontaneous invasive birds in France since 1950 were collected to determine the relation between geographical range and spontaneous invasions of French biogeographical areas. Second, the urban context, assumed to be free of immigration, was used to focus on this relation during the establishment and spread of species. For all species recorded, we determined the geographical range from an atlas, measured as the distribution range area RA (occupied area in km²) and the latitudinal range LR (km from north to south). Our results on spontaneous invaders show that the geographical range, especially RA, could help to predict the extent of an invasion once it has started. In the urban context, RA and LR discriminated urban colonists from urban avoiders, which supported the link between the geographical range and establishment/spread success. The geographical range participates, with other traits, in defining an ‘ideal invader’. We suggest that the dynamics of the invasion process i.e., considering each step of invasion rather than an entity, should be an important conceptual tool for future predictive studies.     

Contributions of muscles and passive dynamics to swing initiation over a range of walking speeds

Stiff-knee gait is a common walking problem in cerebral palsy characterized by insufficient knee flexion during swing. To identify factors that may limit knee flexion in swing, it is necessary to understand how unimpaired subjects successfully coordinate muscles and passive dynamics (gravity and velocity-related forces) to accelerate the knee into flexion during double support, a critical phase just prior to swing that establishes the conditions for achieving sufficient knee flexion during swing. It is also necessary to understand how contributions to swing initiation change with walking speed, since patients with stiff-knee gait often walk slowly. We analyzed muscle-driven dynamic simulations of eight unimpaired subjects walking at four speeds to quantify the contributions of muscles, gravity, and velocity-related forces (i.e. Coriolis and centrifugal forces) to preswing knee flexion acceleration during double support at each speed. Analysis of the simulations revealed contributions from muscles and passive dynamics varied systematically with walking speed. Preswing knee flexion acceleration was achieved primarily by hip flexor muscles on the preswing leg with assistance from biceps femoris short head. Hip flexors on the preswing leg were primarily responsible for the increase in preswing knee flexion acceleration during double support with faster walking speed. The hip extensors and abductors on the contralateral leg and velocity-related forces opposed preswing knee flexion acceleration during double support.