Scaling of wingbeat frequency with body mass in bats and limits to maximum bat size.

The ability to fly opens up ecological opportunities but flight mechanics and muscle energetics impose constraints, one of which is that the maximum body size must be kept below a rather low limit. The muscle power available for flight increases in proportion to flight muscle mass and wingbeat frequency. The maximum wingbeat frequency attainable among increasingly large animals decreases faster than the minimum frequency required, so eventually they coincide, thereby defining the maximum body mass at which the available power just matches up to the power required for sustained aerobic flight. Here, we report new wingbeat frequency data for 27 morphologically diverse bat species representing nine families, and additional data from the literature for another 38 species, together spanning a range from 2.0 to 870 g. For these species, wingbeat frequency decreases with increasing body mass as M(b)(-0.26). We filmed 25 of our 27 species in free flight outdoors, and for these the wingbeat frequency varies as M(b)(-0.30). These exponents are strikingly similar to the body mass dependency M(b)(-0.27) among birds, but the wingbeat frequency is higher in birds than in bats for any given body mass. The downstroke muscle mass is also a larger proportion of the body mass in birds. We applied these empirically based scaling functions for wingbeat frequency in bats to biomechanical theories about how the power required for flight and the power available converge as animal size increases. To this end we estimated the muscle mass-specific power required for the largest flying extant bird (12-16 kg) and assumed that the largest potential bat would exert similar muscle mass-specific power. Given the observed scaling of wingbeat frequency and the proportion of the body mass that is made up by flight muscles in birds and bats, we estimated the maximum potential body mass for bats to be 1.1-2.3 kg. The largest bats, extinct or extant, weigh 1.6 kg. This is within the range expected if it is the bat characteristic flight muscle mass and wingbeat frequency that limit the maximum body mass in bats. It is only a tenth the mass of the largest flying extant bird.

To minimize foraging time, use high-efficiency, energy-expensive search and capture methods when food is abundant but low-efficiency, low-cost methods during food shortages.

Based on a mathematical model, I show that the amount of food in the habitat determines which among alternative methods for search of prey, respectively, for pursuit-and-capture give the shortest daily foraging time. The higher the locomotor activity, the higher the rate of energy expenditure and the larger the habitat space a predator can search for prey per time unit. Therefore, I assume that the more efficient a foraging method is, the higher its rate of energy expenditure. Survival selection favors individuals that use foraging methods that cover their energy needs in the shortest possible time. Therefore, I take the optimization criterion to be minimization of the daily foraging time or, equivalently, maximization of the rate of net energy gain. When time is limiting and food is in short supply, as during food bottleneck periods, low-efficiency, low-cost foraging methods give shorter daily foraging times than high-efficiency, energy-expensive foraging methods. When time is limiting, food is abundant and energy needs are large, as during reproduction, high-efficiency high-cost foraging methods give shorter daily foraging times than low-efficiency low-cost foraging methods. When time is not limiting, food is abundant, and energy needs are small, the choice of foraging method is not critical. Small animals have lower rates of energy expenditure for locomotion than large animals. At a given food density and with similar diet, small animals are therefore more likely than large ones to minimize foraging time by using high-efficiency energy-expansive foraging methods and to exploit patches and sites that require energy-demanding locomotion modes. Survival selection takes place at food shortages, while low-efficiency low-cost foraging methods are used, whereas reproduction selection occurs when food is abundant and high-efficiency energy-expensive foraging methods do better. In seasonal environments, selection therefore acts on different foraging methods at different times. Morphological adaptation to one method may oppose adaptation to another. Such conflicts select against foraging and morphological specialization and tend to give species-poor communities of year-round resident generalists. But a stable year-round food supply favors specialization, niche narrowing, and dense species packing.

Scaling for stress similarity and distorted-shape similarity in bending and torsion under maximal muscle forces concurs with geometric similarity among different-sized animals.

When geometric similarity, or isometry, prevails among animals of different sizes their form and proportions are similar. Weight increases as the cube of the length dimension, while cross-sectional areas increase as its square, so in load-bearing structural elements the stress, caused by the body weight, increases in direct proportion to the length dimension, both for pure axial loads and for transverse bending and torsional loads. On this account, large body sizes would be expected to set up compensatory selection on the proportions of supporting structures, making them disproportionately thicker as required to maintain similar, size-independent safety factors against breakage. Most previous scaling theories have assumed that the strength of support elements has evolved with respect to loads due to the body weight. But then, from the arguments above, a scaling principle different from the geometric similarity rule would be required in order for safety factors to remain similar among different-sized animals. Still, most comparable animals of 'similar kind' scale in accordance with the geometric similarity rule. Here, we instead argue that muscle forces cause much larger loads on structural support elements during maximum performance events (such as during prey capture or escape from predators) than do loads dictated by the body weight (such as during cruising locomotion), and that structural strength therefore might evolve with respect to maximal muscle forces rather than to the body weight. We explore how the transverse and longitudinal lengths of structural support elements must scale to one another, and to muscle transverse length, in order to satisfy each of the following, functionally based, similarity principles for support elements placed in bending, or in torsion, by maximal muscle forces during locomotion: (1) similarity in axial stress, or (2) in torsional shear stress, and (3) similarity in bent shape, or (4) in twisted shape. A dimensional relationship that satisfies all four conditions actually turns out to be the geometric similarity rule. These functional attributes may therefore help to explain the prevalence of geometric similarity among animals. Conformance of different-sized species with the geometric similarity principle has not been directly selected for as such, of course, but may have arisen as a by-product of adaptation in morphological proportions, following upon selection, in each separate species-lineage, for adequate and similar safety factors against breakage, and similar optimal distorted shapes, of structural support elements placed in bending, or in torsion, by maximal muscle forces.

Delta-wing function of webbed feet gives hydrodynamic lift for swimming propulsion in birds.

Most foot-propelled swimming birds sweep their webbed feet backwards in a curved path that lies in a plane aligned with the swimming direction. When the foot passes the most outward position, near the beginning of the power stroke, a tangent to the foot trajectory is parallel with the line of swimming and the foot web is perpendicular to it. But later in the stroke the foot takes an increasingly transverse direction, swinging towards the longitudinal axis of the body. Here we show that, early in the power stroke, propulsion is achieved mostly by hydrodynamic drag on the foot, whereas there is a gradual transition into lift-based propulsion later in the stroke. At the shift to lift mode, the attached vortices of the drag-based phase turn into a starting vortex, shed at the trailing edge, and into spiralling leading-edge vortices along the sides of the foot. Because of their delta shape, webbed feet can generate propulsive forces continuously through two successive modes, from drag at the beginning of the stroke, all the way through the transition to predominantly lift later in the stroke.

Reactivity of smooth-muscle antibodies, surface ultrastructure, and mobility in cells of human hematopoietic cell lines.

Seventeen human hematopoietic cell lines were tested by indirect immunofluorescence (IF) for reactivity with human serum containing smooth-muscle antibodies (SMA). The correlation of the IF pattern to the cell surface ultrastructure was revealed by scanning electron microscopy (SEM). Lymphoma cells, viewed by SEM, had short villi over the entire cell surface, but, by IF, showed a type of membrane fluorescence. Cells of lymphoblastoid lines had thin, long surface villi, sometimes asymmetric but most often distributed over the whole cell surface. Myeloma and leukemia cells, which had few membrane villi but a surface covered by "blebs" as revealed by SEM, demonstrated, by IF, only a few stub-like projections extending from the surface. Time-lapse cinematography revealed that the intensity and pattern of SMA staining were also correlated to the degree of motility. Indirect IF with human SMA-positive serum might be used in the classification of cell lines derived from human hematopoietic tissue.

Evolution of enlarged body size of coal tits Parus ater in geographic isolation from two larger competitors, the crested tit Parus cristatus and the willow tit Parus montanus, on six Scandinavian islands.

Here, we report that on six widely separated Scandinavian islands, the coal tit Parus ater has evolved morphologically in the direction of two absent competitors, the crested tit P. cristatus and the willow tit P. montanus, to the effect that it is up to 10% larger in linear dimensions than conspecifics on the adjacent Swedish mainland, where all three species coexist. The large size is genetically determined, as ascertained by clutch exchange experiments between island and mainland nests. We conclude that the increased size of P. ater in places where it is geographically isolated from its larger congeners is the result of evolutionary adaptation, due ultimately to relaxed interspecific competition. On the islands, P. ater has evolved into a medium-sized generalist, with selection pressures likely governed by the following causal relationships. When competitors are lacking, P. ater takes over the foraging space of the absentees. The enlarged food base allows higher population densities, which intensifies intraspecific interference competition. This, in turn, selects for increased body size. When P. ater coexists with its larger congeners, it occupies peripheral foraging sites in trees, which requires excellent manoeuvrability and energy-expensive locomotion modes. Reduction of body size increases locomotor capacity for mechanical and aerodynamic reasons and lowers energy consumption, so small size is favoured in sympatry. But in geographic isolation, P. ater exploits the tree periphery less and the inner tree regions more, and it also adopts the easier locomotion modes of the absent species. Therefore, selection for manoeuvrability and a small body size is relaxed. The new selection regime shifts the balance between opposing selection forces towards a larger body size. We were able to test 11 alternative hypotheses and available evidence conclusively eliminates them all. As a result, here, evolution could be predicted regarding both direction and amount of change.

Non-specific precipitin reactions of IgG at low ionic strength.

Precipitin reactions apparently not involving specific antibodies were obtained in immunodiffusion experiments performed at low salt concentration between IgG and the muscle proteins, actin and tropomyosin. The precipitates, which dissolved at physiologic ionic strength, may result from electrostatic interaction of molecules of different net charge and different distribution and number of charged groups.

A radioimmunoassay for determination of anti-actin antibodies.

The reaction of spontaneously occurring human anti-human antibodies and experimentally produced rabbit anti-actin antibodies was investigated in a solid-phase radioimmunoassay (RIA). Three structurally different in vitro forms of actin monomeric G-actin filamentous F-actin and aggregated denatured actin were used as antigens. Human anti-actin antibodies reacted with F- and G-actin but not with aggregated actin, while rabbit anti-actin antibodies gave a strong reaction with all 3 forms of actin indicating differences in antibody specificities. The results of the anti-actin RIA were compared with those obtained by indirect immunofluorescence (IFL) on cryostat sections of rat stomach. The anti-actin RIA discriminated between patients' sera and control sera in most cases, although the indirect IFL test gave more conclusive results. The seemingly low sensitivity of the anti-actin RIA compared with that of indirect IFL test for detection of human anti-actin antibodies is probably due to favourable antigen distribution in tissue, not available in the solid phase. The anti-actin RIA was able to detect anti-actin antibodies in 8 out of 8 immunized rabbits although only two produced antibodies detectable by indirect IFL. The differences in reactivity between the two methods may depend on the presence of aggregated denatured actin in the antigen preparation used for immunization and exposure of the corresponding antigenic determinants of actin on the solid phase.

Immunohistochemical staining of normal and Graves' extraocular muscle.

Extraocular muscle biopsies from normal individuals and five patients with Graves' ophthalmopathy were analyzed by immunohistochemical staining. Fibroblasts in normal extraocular muscle as well as Graves' extraocular muscles expressed HLA-class II antigens, but the muscle cells did not. There was an increase of interstitial tissue in Graves' extraocular muscles but no visible damage to the muscle cells. In four of the biopsies from Graves' patients the cellular reaction was very weak. In the fifth patient the reaction was more pronounced with macrophages predominating, but with few lymphocytes and almost equal amounts of B and T cells. We could not confirm the earlier described specific extraocular muscle antibodies in sera from Graves' patients and conclude that there seems to be an activation of orbital fibroblasts in Graves' ophthalmopathy. This may contribute to the pathogenesis of the disease.

Mortality and morbidity from invasive bacterial infections during a clinical trial of acellular pertussis vaccines in Sweden.

A double blind placebo-controlled efficacy trial of two acellular pertussis vaccines was conducted in 3801 6- to 11-month-old children. Four vaccinated children died during 7 to 9 months follow-up as a result of Haemophilus influenzae type b meningitis, heroin intoxication with concomitant pneumonia, suspected septicemia, and Neisseria meningitidis Group B septicemia. From the actual death rate in children belonging to the same birth cohort in Sweden that could have been eligible for the trial, one death was expected among vaccinated children. Several investigations were carried out to examine the possibility that the deaths could be causally related to the vaccination. The relative risk for hospitalization due to systemic or respiratory infections was 1.07 (95% confidence interval, 0.95 to 1.20) and 0.83 (95% confidence interval, 0.64 to 1.08) in the vaccine groups as compared with the placebo group. Subsets of the population were studied for signs of immunosuppression. There was no indication of immunoglobulin deficiency or any sign of clinically significant leukopenia or lymphocytosis in vaccine recipients. The results of this analysis provide no evidence for a causal relation between vaccination with the studied acellular pertussis vaccines and altered resistance to invasive disease caused by encapsulated bacteria. The hypothesis that the two variables are related, however, cannot be refuted from these data.

Anti-DNA antibody synthesis after bone marrow transplantation: implications for IgG subclass restrictivity and pathogenicity of autoantibodies.

Two patients developed antinuclear antibodies (ANA) including antibodies directed against double-stranded DNA (dsDNA) after bone marrow transplantation. In one of the patients very high levels of IgM, IgG as well as IgA anti-dsDNA were found during 6 months in the absence of symptoms of systemic lupus erythematosus (SLE). The other patient made IgM anti-dsDNA antibodies for a period of more than 3 years, also in the absence of SLE symptoms. The ANA were restricted to the IgG1 and IgG3 isotypes as is the case in SLE but did not express idiotypes commonly found in this autoimmune disease. The occurrence of these antibodies may reflect a non-antigen induced expansion of the existing donor B-lymphocyte repertoire.

Three-year follow-up of patients with pulmonary tuberculosis in Guinea-Bissau, West Africa.

SETTING: Raoul Follereau Hospital, Bissau, Guinea-Bissau. OBJECTIVE: To study the long-term outcome of patients with bacteriologically verified tuberculosis (TB), with or without human immunodeficiency virus (HIV) co-infection. DESIGN: Sputum samples were collected from all patients referred to the hospital with clinical symptoms of pulmonary tuberculosis. Direct microscopy and culture was performed at the Health Laboratory. Patients with a culture positive for Mycobacterium tuberculosis were followed for 3 years, and underlying factors were analysed regarding the outcome of treatment. A group of sex and age-matched HIV-negative individuals was used as controls. RESULTS: Of 206 bacteriologically verified pulmonary TB patients, 168 were followed up. Antibodies to HIV-2 were found in 33 patients (19.6%); eight patients (4.8%) had antibodies to HIV-1 or showed dual reactivity. Of 149 patients discharged to follow ambulatory treatment, the survival rate of HIV-2-positive patients was 42.3% (11/26) and for HIV-negative patients it was 81.9% (95/116). The difference in survival between HIV-2-positive and HIV-negative patients was highly significant (P < 0.00001). HIV-negative TB patients had a significantly higher mortality than their controls (mortality ratio 3.75, 95% confidence interval 1.58-8.90). Most patients who survived, regardless of HIV status, also became free from symptoms compatible wtih pulmonary TB. CONCLUSION: Although the mortality rate among HIV-positive TB patients was very much higher than among HIV-negative patients, there are weighty arguments for active contact tracing and effective treatment of all TB patients.

Anticardiolipin and complement activation: relation to clinical symptoms.

Anticardiolipin antibodies which seldom occur in healthy persons are frequently found in systemic lupus erythematosus (SLE). Their presence, especially at high levels (greater than 10 units) are often accompanied by thromboembolic manifestations as well as thrombocytopenia and recurrent abortions. The incidence of cardiolipin antibodies was as great in SLE as in women with clinically unexplained recurrent abortions. The anticardiolipin levels remained unchanged in most patients for long periods and were remarkably unaffected by disease activity and therapy. On the other hand, in several cases the activated partial thromboplastin time which was prolonged in most patients with persistently high cardiolipin antibody levels, approached normal during treatment with prednisolone and salicylic acid. This seemed to facilitate a successful outcome of pregnancy. Absorption of sera with cardiolipin and other negatively charged phospholipids but not with uncharged phospholipids abolished the anticardiolipin activity in enzyme linked immunosorbent assay. In most sera with cardiolipin antibody levels greater than 10 units complement activation by the classical pathway could be demonstrated. Whether the anticardiolipin antibodies contributed to complement activation could not be determined.