Warming rates as a function of body size in periodic endotherms

Summary Warm-up rates and cooling constants were measured in several groups of insects over a wide range of thoracic weights. Vertebrate heterotherms show an inverse dependence of warm-up rate on body weight, but in insects warm-up rate increases with increasing size over the range studied (Figures 1-4, 8). Equations are derived, based on known or estimated relations of heat loss and production to body weight, that predict warm-up rates in insects and mammals with reasonable accuracy. Both weight-specific heat production and loss increase with decreasing body size, but heat loss increases more rapidly. At the size range of insects, loss is so rapid that metabolism cannot fully compensate. Then warm-up rate is constant or decreases with diminishing size.     

Short-term energy conservation in endotherms in relation to body mass, habits, and environment

(1) The lower limit of thermoneutrality in some tropical, arboreal mammals that weigh over 2 kg is defined by a thermal conductance greater than the minimum. (2) The reduction in thermal conductance at low ambient temperatures is accomplished by peripheral vasoconstriction. (3) A similar reduction in thermal conductance is found in some birds, often at smaller masses than in mammals. (4) The combination of low conductances with low basal rates of metabolism facilitates energy conservation in species that have limited supplies of available energy. (5) The reduction of conductance at low ambient temperatures is one of the few physiological responses limited to intermediate body masses.     

Comparison of stimulus-response (V-log I) functions in five types of lepidopteran compound eyes (46 species)

Summary Stimulus intensity-response relations (V-log I curves) were electrophysiologically (ERG) determined for the compound eyes of 46 lepidopteran species belonging to five different groups: butterflies (22 species), hesperids (3 species), diurnal sphingids (2 species), diurnal moths (3 species) and nocturnal moths (16 species). The V-log I curves were fitted to the Naka and Rushton equation, in whichn represents the slope of the linear part of each curve. The slopes so determined range fromn=0.35 (the shallowest slope) in nocturnal moths with the greatest dynamic range ton=0.54 (the steepest slope) in diurnal moths andn=0.53 in butterflies both of which have narrow dynamic range. Hesperids (n=0.41) and diurnal sphingids (n=0.38) have intermediate values between butterflies and nocturnal moths.The ratio of rhabdom to retinula volume is significantly higher in nocturnal moths (70–75%), however, those of butterflies and of diurnal moths are very small (2–5%), and hesperids and diurnal sphingids show intermediate ratio (ca. 25%).The slopes of V-log I curves are inversely proportional to the ratio of rhabdom to retinula volume in the various eye types. In all groups except diurnal moths, the light intensities which produce maximal and saturated responses are nearly the same, therefore the nocturnal moths which have the lowest threshold to light increase their sensitivity to dim light mainly by decreasing the slopes of V-log I curves.     

Life history patterns in birds and mammals and their evolutionary interpretation

Summary It is argued that allometric principles account for most of the observed variation in the life history patterns amongst birds. To test this contention it is shown that traits such as incubation time, growth rates, age at first reproduction, lifespan, clutch weight and egg weight all scale to body weight with exponents similar to those found for analogous traits in mammals. It is then shown that most of the variation amongst bird taxa and between birds and mammals based on body weight allometry can be explained by variations in brain size, body temperature and metabolic rate, consistent with theories of growth and ageing derived from mammalian studies. Finally, it is suggested that the evidence for life histostory allometry is sufficiently strong that it argues for a more epigenetic view of life history patterns and their evolution than is generally conceded in most adaptation theories.     

An allometric study of pulmonary morphometric parameters in birds, with mammalian comparisons

Comprehensive pulmonary morphometric data from 42 species of birds representing ten orders were compared with those of other vertebrates, especially mammals, relating the comparisons to the varying biological needs of these avian taxa. The total lung volume was strongly correlated with body mass. The volume density of the exchange tissue was lowest in the charadriiform and anseriform species and highest in the piciform, cuculiform and passeriform species. The surface area of the blood-gas (tissue) barrier, the volume of the pulmonary capillary blood and the total morphometric pulmonary diffusing capacity were all strongly correlated with body mass. The harmonic mean thickness of both the blood-gas (tissue) barrier and the plasma layer were weakly correlated with body mass. The mass-specific surface area of the blood-gas (tissue) barrier (surface area per gram body mass) and the surface density of the blood-gas (tissue) barrier (i.e. its surface area per unit volume of exchange tissue) were inversely correlated (though weakly) with body mass. The passeriform species exhibited outstanding pulmonary morphometric adaptations leading to a high specific total diffusing capacity per gram body mass, consistent with the comparatively small size and energetic mode of life which typify passeriform birds. The relatively inactive, ground-dwelling domestic fowl (Gallus gallus) had the lowest pulmonary diffusing capacity per gram body mass. The specific total lung volume is about 27% smaller in birds than in mammals but the specific surface area of the blood-gas (tissue) barrier is about 15% greater in birds. The ratio of the surface area of the tissue barrier to the volume of the exchange tissue was also much greater in the birds (170-305%). The harmonic mean thickness of the tissue barrier was 56-67% less in the birds, but that of the plasma layer was about 66% greater in the birds. The pulmonary capillary blood volume was also greater (22%) in the birds. Except for the thickness of the plasma layer, these morphometric parameters all favour the gas exchange capacity of birds. Consequently, the total specific mean morphometric pulmonary diffusing capacity for oxygen was estimated to be about 22% greater in birds than in mammals of similar body mass. This estimate was obtained by employing oxygen permeation constants for mammalian tissue, plasma and erythrocytes, as avian constants were not then available.(ABSTRACT TRUNCATED AT 400 WORDS)     

The relative importance of olfaction and vision in a diurnal and a nocturnal hawkmoth

Nectar-feeding animals can use vision and olfaction to find rewarding flowers and different species may give different weight to the two sensory modalities. We have studied how a diurnal or nocturnal lifestyle affects the weight given to vision and olfaction. We tested naïve hawkmoths of two species in a wind tunnel, presenting an odour source and a visual stimulus. Although the two species belong to the same subfamily of sphingids, the Macroglossinae, their behaviour was quite different. The nocturnal Deilephila elpenor responded preferably to the odour while the diurnal Macroglossum stellatarum strongly favoured the visual stimulus. Since a nocturnal lifestyle is ancestral for sphingids, the diurnal species, M. stellatarum, has evolved from nocturnal moths that primarily used olfaction. During bright daylight visual cues may have became more important than odour.     

Scaling of insulation in seals and whales

We describe scaling of morphological variables that influence total insulation in eight species of marine mammals ranging in average size from 35 to 30000 kg. We also calculate total heat loss and the partitioning of heat loss through the body surface and appendages. For the eight species investigated, heat loss in 0°C water is appreciably higher than the predicted basal metabolic rates for small species such as the ringed seal. Rorquals, on the other hand, will probably not need to raise their metabolic rates to keep warm. At rest, 10–30% of the heat production of a resting animal is lost through flippers, fins and flukes. This amount can increase to 70–80% during moderate exercise. Whole-body conductance scales with body size in the same way in marine as in terrestrial mammals, although conductance is higher for a given body size in a marine mammal.     

Different effects of sphingid and noctuid moths on the fecundity ofPlatanthera metabifolia (Orchidaceae) in Hokkaido

The fecundity ofPlatanthera metabifolia was investigated in relation to different types of behavior and morphology in both noctuid and sphingid pollinator moths. Low capsule set in the native habitats resulted from low activity of pollinating moths. From different patterns of capsule formation on spikes, pollinated spikes could be classified into sphingid-pollinated and noctuid-pollinated types. The contributions of sphingids to capsule set were nearly constant at the three study sites. High percentage capsule set at one site was linked with high noctuid activity. Different preferences of sphingids and noctuids as to spike features were detected: sphingids selected spikes with large numbers of flowers in early stages of flowering. Flowers with different spur length were equally pollinated by sphingids. On the other hand, noctuids selected spikes with short and medium-sized spurs in the late stage of flowering. The size and density of spikes scarcely affected the pollination activity of noctuids. Selection pressure upon spike size and spur length in relation to sphingid pollination was suggested. The possibility of local differentiation in spur length due to activity of noctuids was discussed.     

Morphometrics of the avian small intestine compared with that of nonflying mammals: a phylogenetic approach

Flying animals may experience a selective constraint on gut volume because the energetic cost of flight increases and maneuverability decreases with greater digesta load. The small intestine is the primary site of absorption of most nutrients (e.g., carbohydrates, proteins, fat) in both birds and mammals. Therefore, we used a phylogenetically informed approach to compare small intestine morphometric measurements of birds with those of nonflying mammals and to test for effects of diet within each clade. We also compared the fit of nonphylogenetic and phylogenetic models to test for phylogenetic signal after accounting for effects of body mass, clade, and/or diet. We provide a new MATLAB program (Regressionv2.m) that facilitates a flexible model-fitting approach in comparative studies. As compared with nonflying mammals, birds had 51% less nominal small intestine surface area (area of a smooth bore tube) and 32% less volume. For animals <365 g in body mass, birds also had significantly shorter small intestines (20%-33% shorter, depending on body mass). Diet was also a significant factor explaining variation in small intestine nominal surface area of both birds and nonflying mammals, small intestine mass of mammals, and small intestine volume of both birds and nonflying mammals. On the basis of the phylogenetic trees used in our analyses, small intestine length and nominal surface area exhibited statistically significant phylogenetic signal in birds but not in mammals. Thus, for birds, related species tended to be similar in small intestine length and nominal surface area, even after accounting for relations with body mass and diet. A reduced small intestine in birds may decrease the capacity for breakdown and active absorption of nutrients. Birds do not seem to compensate for reduced digestive and absorptive capacity via a longer gut retention time of food, but we found some evidence that birds have an increased mucosal surface area via a greater villus area, although not enough to compensate for reduced nominal surface area. We predict that without increased rate of enzyme hydrolysis and/or mediated transport and without increased passive absorption of water-soluble nutrients, birds may operate with a reduced digestive capacity, compared with that of nonflying mammals, to meet an increase in metabolic needs (i.e., a reduced spare capacity).     

Cell size is positively correlated between different tissues in passerine birds and amphibians,but not necessarily in mammals

We examined cell size correlations between tissues, and cell size to body mass relationships in passerine birds, amphibians and mammals. The size correlated highly between all cell types in birds and amphibians; mammalian tissues clustered by size correlation in three tissue groups. Erythrocyte size correlated well with the volume of other cell types in birds and amphibians, but poorly in mammals. In birds, body mass correlated positively with the size of all cell types including erythrocytes, and in mammals only with the sizes of some cell types. Size of mammalian erythrocytes correlated with body mass only within the most taxonomically uniform group of species (rodents and lagomorphs). Cell volume increased with body mass of birds and mammals to less than 0.3 power, indicating that body size evolved mostly by changes in cell number. Our evidence suggests that epigenetic mechanisms determining cell size relationships in tissues are conservative in birds and amphibians, but less stringent in mammals. The patterns of cell size to body mass relationships we obtained challenge some key assumptions of fractal and cellular models used by allometric theory to explain mass-scaling of metabolism. We suggest that the assumptions in both models are not universal, and that such models need reformulation.     

Food habits and the basal rate of metabolism in birds

Summary The correlation of basal rate of metabolism with various factors is examined in birds. Chief among these is body mass. As in mammals, much of the remaining variation in basal rate among birds is associated with food habits. Birds other than passerines that feed on grass, nectar, flying insects, or vertebrates generally have basal rates that are similar to mammals of the same mass and food habits. In contrast, most invertebrate-eating birds that weigh over 100 g have higher basal rates than equally-sized, invertebrate-eating mammals. The high basal rates of small passerines equal those of small mammals that do not enter torpor and represent the minimal cost of continuous endothermy. Large passerines and small procellariiforms, charadriiforms, and psittaciforms generally have higher basal rates than mammals with the same mass and food habits. The high basal rates of passerines (in combination with altricial habits) may have significance in permitting high post-natal growth rates and the exploitation of seasonally abundant resources. These interrelations may contribute to the predominance of passerines in temperate land environments.     

Retinular fine structure in compound eyes of diurnal and nocturnal sphingid moths

Summary Retinular fine structure has been compared in the superposition compound eyes of three sphingid moths, one nocturnal, Cechenena, and two diurnal, Cephonodes and Macroglossum. Cechenena and Cephonodes have tiered retinas with three kinds of retinular cells: two distal, six regular and one basal. The distal retinular cells in Cechenena are special in having a complex partially intracellular rhabdomere not present in Cephonodes. Macroglossum lacks the distal retinular cell. In Cephonodes a unique rhabdom type, formed by the six regular retinular cells in the middle region of the retinula, is divided into three separate longitudinal plates arranged closely parallel to one another. Their constituent microvilli are consequently all nearly unidirectional. The ratio of rhabdom volume to retinular cell volume in the two diurnal sphingids is 10–27%; this is about the same as that (25%) of skipper butterflies, but significantly smaller than in the nocturnal Cechenena (60%). In the diurnal sphingids retinular cell membranes show elongate meandering profiles with septate junctions between adjacent retinular cells. From the comparative fine structure of their eyes the diurnal sphingids and the skippers would appear to be phylogenetically closely related.Supported in part by grants from Ministry of Education Japan (Special Project Research in Animal Behaviors)     

The maximum oxygen consumption and aerobic scope of birds and mammals: getting to the heart of the matter

Resting or basal metabolic rates, compared across a wide range of organisms, scale with respect to body mass as approximately the 0.75 power. This relationship has recently been linked to the fractal geometry of the appropriate transport system or, in the case of birds and mammals, the blood vascular system. However, the structural features of the blood vascular system should more closely reflect maximal aerobic metabolic rates rather than submaximal function. Thus, the maximal aerobic metabolic rates of birds and mammals should also scale as approximately the 0.75 power. A review of the literature on maximal oxygen consumption and factorial aerobic scope (maximum oxygen consumption divided by basal metabolic rate) suggests that body mass influences the capacity of the cardiovascular system to raise metabolic rates above those at rest. The results show that the maximum sustainable metabolic rates of both birds and mammals are similar and scale as approximately the 0.88 +/- 0.02 power of body mass (and aerobic scope as approximately the 0.15 +/- 0.05 power), when the measurements are standardized with respect to the differences in relative heart mass and haemoglobin concentration between species. The maximum heart beat frequency of birds and mammals is predicted to scale as the -0.12 +/- 0.02 power of body mass, while that at rest should scale as -0.27 +/- 0.04.     

An allometric comparison of the mitochondria of mammalian and reptilian tissues: The implications for the evolution of endothermy

Summary The effects of body size and phylogeny on metabolic capacities were examined by comparing the mitochondrial capacities of 6 mammalian and 4 reptilian species representing 100-fold body weight ranges. The mammals examined included 3 eutherian, 2 marsupial and a monotreme species and the reptiles 2 saurian, 1 crocodilian and 1 testudine species. The tissues examined were liver, kidney, brain, heart, lung and skeletal muscle. Allometric equations were derived for tissue weights, mitochondrial volume densities, internal mitochondrial membrane surface area densities, tissue mitochondrial membrane surface areas both per gram and per total tissue and summated tissue mitochondrial membrane surface areas. For the mammals and reptiles studied a 100% increase in body size resulted in average increases of 68% in internal organ size and 107% in skeletal muscle mass. Similarly, total organ mitochondrial membrane surface areas increase in mammals and reptiles by an average 54% and for skeletal muscle by an average 96%. These values are similar to increases in standard (54 and 71%) and maximum (73 and 77%) organismal metabolism values found by other authors for mammals and reptiles respectively. Although the allometric exponents (or rates of change with increasing body size) of the mitochondrial parameters in mammals and reptiles are statistically the same, in general the total amount of mitochondrial membrane surface area in the mammalian tissues are four times greater than found in the reptilian tissues. These differences were not the result of any single ‘quantum’ factor but are the result of the mammals having relatively larger tissues with a greater proportion of their volume occupied by mitochondria and to a lesser extent increases in the internal mitochondrial membrane surface area densities. Mitochondrial volume density from this present study would appear to be the major factor involved in changing weight specific metabolism of tissues both as a result of changes in body size and in the evolution of endothermy in mammals from reptiles.     

Tyrannosaur ageing

Rate of ageing in tyrannosaurs was calculated from parameters of Weibull functions fitted to survival curves based on the estimated ages at death of fossilized remains. Although tyrannosaurs are more closely related to birds than to mammals, they apparently aged at rates similar to mammals of comparable size. Rate of growth in body mass of tyrannosaurs was similar to that of large mammals, and their rates of ageing were consistent with the estimated extrinsic mortality, which is strongly correlated with the rate of ageing across birds and mammals. Thus, tyrannosaurs appear to have had life histories resembling present-day large terrestrial mammals. Rate of ageing in warm-blooded vertebrates appears to be adjusted in response to extrinsic mortality and potential lifespan, independently of both physiological and developmental rates. However, individuals in species with the slowest rates of ageing suffer the highest proportion of ageing-related mortality, hence potentially strong selection to further postpone senescence. Thus, the longest observed lifespans in birds, tyrannosaurs and mammals might be close to the maximum possible.     

Malagasy birds as hosts for eye-frequenting moths

While tear-feeding in moths on mammals is widespread, there have been no reports of this behaviour in Madagascar and none on birds. We report that a moth, Hemiceratoides hieroglyphica belonging to the Calpini, a generally fruit-feeding or blood-feeding lineage of noctuids, attacks sleeping birds in Madagascar. This moth is able to intrude its sharply tipped proboscis into a closed bird's eye. The proboscis is characterized by a specific armoury of hooks, barbs and spines similar to that in piercing calpines but dissimilar to that in other tear-feeding moths. This is the first report of exploitation of tears by Lepidoptera from the closed eyes of sleeping birds.     

Quantitative observations on the pulmonary anatomy of the domestic Muscovy duck (Cairina moschata)

The lungs of five female domestic Muscovy ducks, mean body weight 1.627 kg, total lung volume 48.07 cm³, were analysed by standard morphometric methods. Principal results obtained are: lung volume per unit body weight, 30.17 cm³/g; volume densities of exchange tissue relative to lung volume, 49.24%, blood capillaries relative to exchange tissue, 29.63%, tissue of the blood gas (tissue) barrier relative to exchange tissue, 5.88%; surface area of the blood-gas (tissue) barrier per unit body weight, 30.04 cm²/g; ratios of the surface area of the blood-gas (tissue) barrier per unit volume of the lung and per unit volume of exchange area, 979 cm²/cm³ and 200.06 mm²/mm³, respectively; harmonic and arithmetic mean thicknesses of the tissue barrier, 0.199 μm and 0.303 μm, respectively. The anatomical diffusing capacity of the tissue barrier for oxygen ( DtO₂ ) and the total pulmonary diffusing capacity ( DLO₂ ), 49.58 ml O₂/min/mmHg/kg and 4.55 ml O₂/min/mm Hg/kg, respectively. The lungs of the domestic Muscovy duck appear to be about as well adapted anatomically for gas exchange as the lungs of wild anatid species, and there is no clear evidence that domestication has been associated with any deterioration in the anatomical capacity for oxygen uptake. The weight-specific anatomical diffusing capacity of the lung for oxygen ( DLO₂/W ) was about 3.6 times greater than the weight-specific physiological value, a factor which falls within the expected range.     

The relationship between growth, food conversion and oxygen consumption in developed and underdeveloped American eels, Anguilla rostrata Lesueur

This study examined the influence of body size and temperature on oxygen consumption and food converstion in juvenile American eels ( Anguilla rostrata ). The weight-specific oxygen consumption rate for underdeveloped eels (18 months old) was significantly higher than the weight-specific oxygen consumption rate of developed eels of the same weight (6 months old). Oxygen consumption rates increased linearly with weight at each experimental temperature (15, 20, 25°C) when data were transformed logarithmically. No significant differences were found among slopes oflog transformed data at varying temperatures. Oxygen consumption was significantly higher at night (2300 h) as compared to morning (0900 h). The results indicate that underdeveloped eels use more energy and use less food less efficiently than developed eels.     

Estimation of cardiac output and stroke volume from thermal equilibration and heartbeat rates in fish

Cardiac output and stroke volume were estimated for a 200 g largemouth blackbass (Micropterus salmoides) by a modified whole-body thermodilution method using the relation between thermal equilibration rates and heartbeat frequencies. The reciprocal of the thermal time constant, k (min^–1), was related to the heartbeat frequency, F (beats min^–1), by the equation k=0.00146 F + 0.309; the slope is the weight-specific stroke volume (ml g^–1) and the intercept is the weight-specific heat transfer constant (cal °C^–1 min^–1 g^–1). Stroke volume was 0.292 ml (0.00146 ml/g body weight), yielding cardiac output values ranging from 44 ml kg^–1 min^–1 (at 30 beats min) to 158 ml kg^–1 min^–1 (at 108 beats min^–1), or 4.4 to 15.8% of body weight. Active (convective) heat transfer due to blood flow constituted an estimated 11 to 34% (mean 22.5%) of total heat transfer, depending on heartbeat frequency; this variability constitutes physiological thermoregulation.     

Historical bird and terrestrial mammal extinction rates and causes

Aim Conservation of species is an ongoing concern. Location Worldwide. Methods We examined historical extinction rates for birds and mammals and contrasted island and continental extinctions. Australia was included as an island because of its isolation. Results Only six continental birds and three continental mammals were recorded in standard databases as going extinct since 1500 compared to 123 bird species and 58 mammal species on islands. Of the extinctions, 95% were on islands. On a per unit area basis, the extinction rate on islands was 177 times higher for mammals and 187 times higher for birds than on continents. The continental mammal extinction rate was between 0.89 and 7.4 times the background rate, whereas the island mammal extinction rate was between 82 and 702 times background. The continental bird extinction rate was between 0.69 and 5.9 times the background rate, whereas for islands it was between 98 and 844 times the background rate. Undocumented prehistoric extinctions, particularly on islands, amplify these trends. Island extinction rates are much higher than continental rates largely because of introductions of alien predators (including man) and diseases. Main conclusions Our analysis suggests that conservation strategies for birds and mammals on continents should not be based on island extinction rates and that on islands the key factor to enhance conservation is to alleviate pressures from uncontrolled hunting and predation.