Functional capacities of marsupial hearts: size and mitochondrial parameters indicate higher aerobic capabilities than generally seen in placental mammals

This study of marsupial hearts explored the aerobic capacities of this group of mammals; recent information suggests that marsupials possess higher aerobic abilities than previously accepted. Characteristics such as heart mass, mitochondrial features and capillary parameters were examined. A comprehensive study of the heart of red kangaroos was included because of the high maximum oxygen consumption of this species. Goats were also included as a reference placental mammal. Marsupials have a heart that is generally larger than that of placentals. The allometric equation for the relationship between heart mass and body mass for marsupials was M_h=7.5M_b^0.944 (M_h in g and M_b in kg); the equivalent equation for placental mammals was M_h=6.0M_b^0.97. Mitochondrial volume density and inner mitochondrial surface density do not differ between the two mammal groups; although capillary parameters indicated a lower capillary volume in marsupials. Heart size appears to be the major difference between the two groups. The overall pattern seen in marsupials is similar to that of "athletic" placentals and indicates a relatively high aerobic potential.Abbreviations BMR basal metabolic rate - c(K,0) tortuosity factor - Jv(c,f) capillary length density - M_b body mass - M_h heart mass - N_A(c,f) numerical capillary density - r_c mean capillary radius - S(im,m) total surface area of inner mitochondrial membranes in the heart - Sv(im,m) surface density of the inner mitochondrial membranes - Sv(im,mt) surface density of inner mitochondrial membranes per unit volume of mitochondria - TEM transmission electron microscope - O₂max maximum aerobic capacity - V(mt,m) total mitochondrial volume - Vv(f,m) volume fraction of muscle occupied by muscle fibres - Vv(mt,f) mitochondrial volume densityCommunicated by I.D. Hume     

Fundamental avian energetics: 2. The ability of birds to change heat loss and explanation of the mass exponent for basal metabolism in homeothermic animals

The maximum ability of birds to generate heat due to increasing metabolism, as a result of both activity and heat stress, was determined in relation to the evaporative and nonevaporative heat losses at various temperatures in passerines and nonpasserines at the beginning and at the end of thermoneutral zones. The minimum (h _min) and maximum (h _max) nonevaporative thermal conductances in both species change similarly depending on the body mass, and the slopes of regression lines in h _min and h _max are identical. At the same time, h _max is approximately four times higher than h _min. Experimental data obtained both in this study and by other authors show that the ratio h _max/h _min = 4 is constant for all homeothermic animals and appears to be a sensible compromise found by the evolution between an increase in activity and the minimum effectiveness profitable for life of the transfer of metabolic power into mechanical power (?? = 1/4) during its fulfillment. An increase in the ratio h _max/h _min, although it allows an animal to augment its daily activity, leads to a reduction in the effectiveness and is, therefore, not used by homeothermic animals. The abilities of birds and mammals to change their heat loss are determined by the ratio h _max/h _min = 4, which is an integrated indicator of the level of development of blood circulation and respiration systems and the degree of development of external covers, as well as the ability of both to change heat loss. In homeothermic animals, this ratio is associated with the body mass exponent in allometric dependences for basal metabolism and determines the efficiency of transfer of metabolic power into mechanical work.     

Fundamental energetics of birds: 1. The maximum ability of birds to change their thermal conductance and the efficiency of metabolic energy transformation into mechanical work

The maximum abilities of birds to dissipate heat with an increase in their metabolic rate as a result of both activity and heat stress have been estimated by an integrated measurement of energy expenditure at rest (measured according to oxygen consumption) and common activity, the so-called existence metabolism (measured according to food consumption) in 26 passerine species, covering the overall order relative to the size range (from goldcrest to raven) and 16 nonpasserine species of the same size range (25?C4000 g). The passerine and nonpasserine species do not differ in the mean change of heat loss in the cases of both maximal (h _min) and minimal (h _max) insulations. Both the minimal (h _min) and maximal (h _max) nonevaporative heat losses in both groups of species display similar dependences on the body weight, and the regression slopes for both h _min and h _max are equal. On the other hand, h _max is approximately fourfold higher as compared with h _min. This demonstrates that birds at the same ambient temperature (T _A) are able to increase fourfold the amount of dissipated heat losses without increasing their evaporative heat loss. An increase in the h _max/h _min ratio suggests a more perfect organization of the systems associated with blood circulation and respiration, which naturally gives great advantages for any life activities, first and foremost, allowing for an increase in activity. The efficiency of metabolic energy transformation into mechanical work during standard existence varies in the studied species from 0.28 to 0.22 in summer and in winter.     

Esterification and hydrolysis of vitamin A in the liver of brook trout (Salvelinus fontinalis) and the influence of a coplanar polychlorinated biphenyl

Recent reports of extremely low retinoid stores in fish living in contaminated river systems prompted an initial investigation of the mechanisms of hepatic storage and mobilization in brook trout. Enzyme characterization in microsomes revealed a lecithin:retinol acyltransferase activity (LRAT) optimum in the alkaline range (pH 9.0; V_max=0.6 nmol per mg prot. h⁻¹; K_m=10.2 μM) which is not known to occur in mammals, in addition to a secondary optimum at pH 6.5 typical of mammals. Acyl CoA:retinol acyltransferase (ARAT) kinetic parameters were quite different to those of mammals. The substrate affinity of trout ARAT (K_m=1.6 μM) was approximately 22-fold greater than that of the rat while maximal velocity (V_max=0.2 nmol per mg prot. h⁻¹) was 18-fold less. Retinyl ester hydrolase activity (REH) was optimal under acid conditions (pH 4.2; V_max=6.6 nmol per mg prot. h⁻¹; K_m=0.6 mM), was inhibited by a bile salt analogue and was greater in males than females. This REH was tentatively categorized as a bile salt-independent, acid retinyl ester hydrolase (BSI-AREH). REH was inhibited in a dose-dependent manner following in vivo exposure to a representative environmental contaminant the coplanar polychlorinated biphenyl (PCB), 3,3′,4,4′-tetrachlorobiphenyl (TCBP). Inhibition may be an indirect effect because enzyme activity was not affected by in vitro exposure of control microsomes. REH inhibition in the brook trout may affect the uptake of retinyl esters (REs) from chylomicron remnants as well as the mobilization of stored REs.     

The energy cost of flight: do small bats fly more cheaply than birds?

Flapping flight is one of the most expensive activities in terms of metabolic cost and this cost has previously been considered equal for the two extant vertebrate groups which evolved flapping flight. Owing to the difficulty of obtaining accurate measurements without disturbing flight performance, current estimates of flight cost within the group of small birds and bats differ by more than a factor of five for given body masses. To minimize the potential problem that flight behaviour may be affected by the measurements, we developed an indirect method of measuring flight energy expenditure based on time budget analysis in which small nectar-feeding bats (Glossophaginae) could continue their natural rhythm of flying and resting entirely undisturbed. Estimates of metabolic flight power based on 172 24-h time and energy budget measurements were obtained for nine individual bats from six species (mass 7–28 g). Metabolic flight power (P_F) of small bats was found to increase with body mass following the relation P_F = 50.2 M^0.771 (r² = 0.96, n = 13, P_F in W, M in kg). This is about 20–25% below the majority of current predictions of metabolic flight cost for small birds. Thus, either the flight cost of small birds is significantly lower than has previously been thought or, contrary to current opinion, small bats require less energy to fly than birds. Accepted: 29 September 1997     

Mechanistic Drivers of Flexibility in Summit Metabolic Rates of Small Birds

Flexible metabolic phenotypes allow animals to adjust physiology to better fit ecological or environmental demands, thereby influencing fitness. Summit metabolic rate (M_sum = maximal thermogenic capacity) is one such flexible trait. Skeletal muscle and heart masses and myocyte metabolic intensity are potential drivers of M_sum flexibility in birds. We examined correlations of skeletal muscle and heart masses and pectoralis muscle citrate synthase (CS) activity (an indicator of cellular metabolic intensity) with M_sum in house sparrows (Passer domesticus) and dark-eyed juncos (Junco hyemalis) to determine whether these traits are associated with M_sum variation. Pectoralis mass was positively correlated with M_sum for both species, but no significant correlation remained for either species after accounting for body mass (M_b) variation. Combined flight and leg muscle masses were also not significantly correlated with M_sum for either species. In contrast, heart mass was significantly positively correlated with M_sum for juncos and nearly so (P = 0.054) for sparrows. Mass-specific and total pectoralis CS activities were significantly positively correlated with M_sum for sparrows, but not for juncos. Thus, myocyte metabolic intensity influences M_sum variation in house sparrows, although the stronger correlation of total (r = 0.495) than mass-specific (r = 0.378) CS activity with M_sum suggests that both pectoralis mass and metabolic intensity impact M_sum. In contrast, neither skeletal muscle masses nor pectoralis metabolic intensity varied with M_sum in juncos. However, heart mass was associated with M_sum variation in both species. These data suggest that drivers of metabolic flexibility are not uniform among bird species.     

Intraspecific Scaling of the Resting and Maximum Metabolic Rates of the Crucian Carp (Carassius auratus)

The question of how the scaling of metabolic rate with body mass (M) is achieved in animals is unresolved. Here, we tested the cell metabolism hypothesis and the organ size hypothesis by assessing the mass scaling of the resting metabolic rate (RMR), maximum metabolic rate (MMR), erythrocyte size, and the masses of metabolically active organs in the crucian carp (Carassius auratus). The M of the crucian carp ranged from 4.5 to 323.9 g, representing an approximately 72-fold difference. The RMR and MMR increased with M according to the allometric equations RMR = 0.212M ^0.776 and MMR = 0.753M ^0.785. The scaling exponents for RMR (b _r) and MMR (b _m) obtained in crucian carp were close to each other. Thus, the factorial aerobic scope remained almost constant with increasing M. Although erythrocyte size was negatively correlated with both mass-specific RMR and absolute RMR adjusted to M, it and all other hematological parameters showed no significant relationship with M. These data demonstrate that the cell metabolism hypothesis does not describe metabolic scaling in the crucian carp, suggesting that erythrocyte size may not represent the general size of other cell types in this fish and the metabolic activity of cells may decrease as fish grows. The mass scaling exponents of active organs was lower than 1 while that of inactive organs was greater than 1, which suggests that the mass scaling of the RMR can be partly due to variance in the proportion of active/inactive organs in crucian carp. Furthermore, our results provide additional evidence supporting the correlation between locomotor capacity and metabolic scaling.     

Respiratory evaporative water loss during hovering and forward flight in hummingbirds

Hummingbirds represent an end point for small body size and water flux in vertebrates. We explored the role evaporative water loss (EWL) plays in management of their large water pool and its use in dissipating metabolic heat. We measured respiratory evaporative water loss (REWL) in hovering hummingbirds in the field (6 species) and over a range of speeds in a wind tunnel (1 species) using an open-circuit mask respirometry system. Hovering REWL during the active period was positively correlated with operative temperature (T_e) likely due to some combination of an increase in the vapor-pressure deficit, increase in lung ventilation rate, and reduced importance of dry heat transfer at higher T_e. In rufous hummingbirds (Selasphorus rufus; 3.3 g) REWL during forward flight at 6 and 10 m/s was less than half the value for hovering. The proportion of total dissipated heat (TDH) accounted for by REWL during hovering at T_e > 40 °C was < 40% in most species. During forward flight in S. rufus the proportion of TDH accounted for by REWL was ~ 35% less than for hovering. REWL in hummingbirds is a relatively small component of the water budget compared with other bird species (< 20%) so cutaneous evaporative water loss and dry heat transfer must contribute significantly to thermal balance in hummingbirds.     

Body temperatures in free-flying pigeons

We examined the relationship between body temperature (T_b) of free flying pigeons and ambient water vapor pressure and temperature. Core or near core T_b of pigeons were measured using thermistors inserted into the cloaca and connected to small transmitters mounted on the tail feathers of free flying tippler pigeons (Columba livia). Wet and dry bulb temperatures were measured using modified transmitters mounted onto free-flying pigeons. These allowed calculation of relative humidity and hence water vapor pressure at flight altitudes. Mean T_b during flight was 42.0 ± 1.3 °C (n = 16). Paired comparisons of a subset of this data indicated that average in-flight T_b increased significantly by 1.2 ± 0.7 °C (n = 7) over that of birds at rest (t = −4.22, P < 0.05, n = 7) within the first 15 min of takeoff. In addition, there was a small but significant increase in T_b with increasing ambient air (T_a) when individuals on replicate flights (n = 35) were considered. Inclusion of water vapor pressure into the regression model did not improve the correlation between body temperature and ambient conditions. Flight T_b also increased a small (0.5 °C) but significant amount (t = 2.827, P < 0.05, n = 8) from the beginning to the end of a flight. The small response of T_b to changing flight conditions presumably reflects the efficiency of convection as a heat loss mechanism during sustained regular flight. The increase in T_b on landing that occurred in some birds was a probable consequence of a sudden reduction in convective heat loss. Accepted: 2 February 1999     

Allometry of the Duration of Flight Feather Molt in Birds

We used allometric scaling to explain why the regular replacement of the primary flight feathers requires disproportionately more time for large birds. Primary growth rate scales to mass (M) as M^0.171, whereas the summed length of the primaries scales almost twice as fast (M^0.316). The ratio of length (mm) to rate (mm/day), which would be the time needed to replace all the primaries one by one, increases as the 0.14 power of mass (M^0.316/M^0.171=M^0.145), illustrating why the time required to replace the primaries is so important to life history evolution in large birds. Smaller birds generally replace all their flight feathers annually, but larger birds that fly while renewing their primaries often extend the primary molt over two or more years. Most flying birds exhibit one of three fundamentally different modes of primary replacement, and the size distributions of birds associated with these replacement modes suggest that birds that replace their primaries in a single wave of molt cannot approach the size of the largest flying birds without first transitioning to a more complex mode of primary replacement. Finally, we propose two models that could account for the 1/6 power allometry between feather growth rate and body mass, both based on a length-to-surface relationship that transforms the linear, cylindrical growing region responsible for producing feather tissue into an essentially two-dimensional structure. These allometric relationships offer a general explanation for flight feather replacement requiring disproportionately more time for large birds.     

Evidence for a Mass Dependent Step-Change in the Scaling of Efficiency in Terrestrial Locomotion

A reanalysis of existing data suggests that the established tenet of increasing efficiency of transport with body size in terrestrial locomotion requires re-evaluation. Here, the statistical model that described the data best indicated a dichotomy between the data for small (<1 kg) and large animals (>1 kg). Within and between these two size groups there was no detectable difference in the scaling exponents (slopes) relating metabolic (E _met) and mechanical costs (E _{mech, CM}) of locomotion to body mass (M _b). Therefore, no scaling of efficiency (E _{mech, CM}/E _met) with M _b was evident within each size group. Small animals, however, appeared to be generally less efficient than larger animals (7% and 26% respectively). Consequently, it is possible that the relationship between efficiency and M _b is not continuous, but, rather, involves a step-change. This step-change in the efficiency of locomotion mirrors previous findings suggesting a postural cause for an apparent size dichotomy in the relationship between E _met and M _b. Currently data for E _{mech, CM} is lacking, but the relationship between efficiency in terrestrial locomotion and M _b is likely to be determined by posture and kinematics rather than body size alone. Hence, scaling of efficiency is likely to be more complex than a simple linear relationship across body sizes. A homogenous study of the mechanical cost of terrestrial locomotion across a broad range of species, body sizes, and importantly locomotor postures is a priority for future research.     

Sugar flux through the flight muscles of hovering vertebrate nectarivores: a review

In most vertebrates, uptake and oxidation of circulating sugars by locomotor muscles rises with increasing exercise intensity. However, uptake rate by muscle plateaus at moderate aerobic exercise intensities and intracellular fuels dominate at oxygen consumption rates of 50 % of maximum or more. Further, uptake and oxidation of circulating fructose by muscle is negligible. In contrast, hummingbirds and nectar bats are capable of fueling expensive hovering flight exclusively, or nearly completely, with dietary sugar. In addition, hummingbirds and nectar bats appear capable of fueling hovering flight completely with fructose. Three crucial steps are believed to be rate limiting to muscle uptake of circulating glucose or fructose in vertebrates: (1) delivery to muscle; (2) transport into muscle through glucose transporter proteins (GLUTs); and (3) phosphorylation of glucose by hexokinase (HK) within the muscle. In this review, we summarize what is known about the functional upregulation of exogenous sugar flux at each of these steps in hummingbirds and nectar bats. High cardiac output, capillary density, and blood sugar levels in hummingbirds and bats enhance sugar delivery to muscles (step 1). Hummingbird and nectar bat flight muscle fibers have relatively small cross-sectional areas and thus relatively high surface areas across which transport can occur (step 2). Maximum HK activities in each species are enough for carbohydrate flux through glycolysis to satisfy 100 % of hovering oxidative demand (step 3). However, qualitative patterns of GLUT expression in the muscle (step 2) raise more questions than they answer regarding sugar transport in hummingbirds and suggest major differences in the regulation of sugar flux compared to nectar bats. Behavioral and physiological similarities among hummingbirds, nectar bats, and other vertebrates suggest enhanced capacities for exogenous fuel use during exercise may be more wide spread than previously appreciated. Further, how the capacity for uptake and phosphorylation of circulating fructose is enhanced remains a tantalizing unknown.     

Alternative versions of the myosin relay domain differentially respond to load to influence Drosophila muscle kinetics

We measured the influence of alternative versions of the Drosophila melanogaster myosin heavy chain relay domain on muscle mechanical properties. We exchanged relay domain regions (encoded by alternative versions of exon 9) between an embryonic (EMB) isoform and the indirect flight muscle isoform (IFI) of myosin. Previously, we observed no effect of exchanging the EMB relay domain region into the flight muscle isoform (IFI-9b) on in vitro actin motility velocity or solution ATPase measurements compared to IFI. However, in indirect flight muscle fibers, IFI-9b exhibited decreased maximum power generation (P_max) and optimal frequency of power generation (f_max) to 70% and 83% of IFI fiber values. The decrease in muscle performance reduced the flight ability and wing-beat frequency of IFI-9b Drosophila compared to IFI Drosophila. Previously, we found that exchanging the flight muscle specific relay domain into the EMB isoform (EMB-9a) prevented actin movement in the in vitro motility assay compared to EMB, which does support actin movement. However, in indirect flight muscle fibers EMB-9a was a highly effective motor, increasing P_max and f_max 2.5-fold and 1.4-fold, respectively, compared to fibers expressing EMB. We propose that the oscillatory load EMB-9a experiences in the muscle fiber reduces a high activation energy barrier between two strongly bound states of the cross-bridge cycle, thereby promoting cross-bridge cycling. The IFI relay domain's enhanced sensitivity to load increases cross-bridge kinetics, whereas the EMB version is less load-sensitive.     

A model of the physiological basis of a multivariate phenotype that is mediated by Ca(2+) signaling and controlled by ryanodine receptor composition

Calcium-signals occur in a wide variety of tissue types - from skeletal, smooth and cardiac muscle to pancreatic and brain tissues. Ca²⁺ signals regulate diverse processes including muscle contraction, hormone secretion, neural communication and gene expression. Together these different tissues and processes form the basis of a multivariate trait. Calcium signals are characterized by Ca²⁺ transients, which are sharp increases in Ca²⁺ concentration over a short period of time. In this paper we derive and analyze a model of Ca²⁺ transients for skeletal muscle, neurons and cardiac tissue based on underlying biophysical principles. Tissue differentiation in our model and in nature comes about by varying the ryanodine receptor (RyR) channel composition of tissues. In vertebrates, there are typically three types of RyR channels (labeled RyR1, RyR2 and RyR3 in mammals and α‐RyR, cardiac-RyR and β‐RyR in birds, amphibians and fish). Different compositions of these three RyR channels generate different Ca²⁺ transient properties. There are four Ca²⁺ transient properties that we measure: maximum amplitude, duration, half duration (D₅₀) and integrated concentration. In agreement with experimental work, our results find that the addition of RyR3 amplifies Ca²⁺ transients in skeletal muscle. An important consequence of shared molecular components between tissue types in a multivariate setting is that the shared components cause individual traits of a multivariate trait to be correlated in function. Here we show how correlations in Ca²⁺ transient properties between tissues can be predicted using an underlying biophysical model.     

Energetic cost of hovering flight in nectar-feeding bats (Phyllostomidae: Glossophaginae) and its scaling in moths, birds and bats

Three groups of specialist nectar-feeders covering a continuous size range from insects, birds and bats have evolved the ability for hovering flight. Among birds and bats these groups generally comprise small species, suggesting a relationship between hovering ability and size. In this study we established the scaling relationship of hovering power with body mass for nectar-feeding glossophagine bats (Phyllostomidae). Employing both standard and fast-response respirometry, we determined rates of gas exchange in Hylonycteris underwoodi (7 g) and Choeronycteris mexicana (13–18 g) during hover-feeding flights at an artificial flower that served as a respirometric mask to estimate metabolic power input. The O₂ uptake rate (V˙ _o2) in ml g⁻¹ h⁻¹ (and derived power input) was 27.3 (1.12 W or 160 W kg⁻¹) in 7-g Hylonycteris and 27.3 (2.63 W or 160 W kg⁻¹) in 16.5-g Choeronycteris and thus consistent with measurements in 11.9-g Glossophagasoricina (158 W kg⁻¹, Winter 1998). V˙ _o2 at the onset of hovering was also used to estimate power during forward flight, because after a transition from level forward to hovering flight gas exchange rates initially still reflect forward flight rates. V˙ _o2 during short hovering events (<1.5 s) was 19.0 ml g⁻¹ h⁻¹ (1.8 W) in 16-g Choeronycteris, which was not significantly different from a previous, indirect estimate of the cost of level forward flight (2.1 W, Winter and von Helversen 1998). Our estimates suggest that power input during hovering flight P _h (W) increased with body mass M (kg) within 13–18-g Choeronycteris (n = 4) as P _h  = 3544 (±2057 SE) M ^{1.76 (±0.21 SE)} and between different glossophagine bat species (n = 3) as P _h  = 128 (±2.4 SE) M ^{0.95 (±0.034 SE)}. The slopes of three scaling functions for flight power (hovering, level forward flight at intermediate speed and submaximal flight power) indicate that: 1. The relationship between flight power to flight speed may change with body mass in the 6–30-g bats from a J- towards a U-shaped curve. 2. A metabolic constraint (hovering flight power equal maximal flight power) may influence the upper size limit of 30–35 g for this group of flower specialists. Mass-specific power input (W kg⁻¹) during hovering flight appeared constant with regard to body size (for the mass ranges considered), but differed significantly (P < 0.001) between groups. Group means were 393 W kg⁻¹ (sphingid moths), 261 W kg⁻¹ (hummingbirds) and 159 W kg⁻¹ (glossophagine bats). Thus, glossophagine bats expend the least metabolic power per unit of body mass supported during hovering flight. At a metabolic power input of 1.1 W a glossophagine bat can generate the lift forces necessary for balancing 7 g against gravitation, whereas a hummingbird can support 4 g and a sphingid moth only 3 g of body mass with the same amount of metabolic energy. These differences in power input were not fully explained by differences in induced power output estimated from Rankine-Froude momentum-jet theory. Accepted: 10 November 1998     

Morphological and kinematic basis of the hummingbird flight stroke: scaling of flight muscle transmission ratio

Hummingbirds (Trochilidae) are widely known for their insect-like flight strokes characterized by high wing beat frequency, small muscle strains and a highly supinated wing orientation during upstroke that allows for lift production in both halves of the stroke cycle. Here, we show that hummingbirds achieve these functional traits within the limits imposed by a vertebrate endoskeleton and muscle physiology by accentuating a wing inversion mechanism found in other birds and using long-axis rotational movement of the humerus. In hummingbirds, long-axis rotation of the humerus creates additional wing translational movement, supplementing that produced by the humeral elevation and depression movements of a typical avian flight stroke. This adaptation increases the wing-to-muscle-transmission ratio, and is emblematic of a widespread scaling trend among flying animals whereby wing-to-muscle-transmission ratio varies inversely with mass, allowing animals of vastly different sizes to accommodate aerodynamic, biomechanical and physiological constraints on muscle-powered flapping flight.     

Molecular cloning and characterization of two novel fructose-specific transporters from the osmotolerant and fructophilic yeast Candida magnoliae JH110

Sugar transport is very critical in developing an efficient and rapid conversion process of a mixture of sugars by engineered microorganisms. By using expressed sequence tag data generated for the fructophilic yeast Candida magnoliae JH110, we identified two fructose-specific transporters, CmFSY1 and CmFFZ1, which show high homology with known fructose transporters of other yeasts. The CmFSY1 and CmFFZ1 genes harbor no introns and encode proteins of 574 and 582 amino acids, respectively. Heterologous expression of the two fructose-specific transporter genes in a Saccharomyces cerevisiae, which is unable to utilize hexoses, revealed that both transporters are functionally expressed and specifically transport fructose. These results were further corroborated by kinetic analysis of the fructose transport that showed that CmFsy1p is a high-affinity fructose–proton symporter with low capacity (K _M?=?0.13?±?0.01 mM, V _max?=?2.1?±?0.3 mmol h^?1 [gdw]^?1) and that CmFfz1p is a low-affinity fructose-specific facilitator with high capacity (K _M?=?105?±?12 mM, V _max?=?8.6?±?0.7 mmol h^?1 [gdw]^?1). These fructose-specific transporters can be used for improving fructose transport in engineered microorganisms for the production of biofuels and chemicals from fructose-containing feedstock.     

Patagial complex evolution in hummingbirds and swifts (Apodiformes): a molecular phylogenetic perspective

Studies of the role of flight in vertebrate evolution often have focused on the propatagial muscle complex because this structure forms the wing's leading edge. However, historical narratives about the evolution of flight anatomy are compromised because traditional higher-level taxonomies typically are based in part on the propatagium itself. To avoid this circularity, I used a consensus molecular phylogeny to examine propatagial evolution in the highly aerial sister groups, hummingbirds and swifts (Apodiformes). Mapping of anatomy on molecular-based phylogeny indicates that structural variation in M .  tensor propatagialis pars brevis (TPB) is congruent with the major subclades of both hummingbirds and swifts. However, the humeral tendon and broad attachment of the fleshy belly of TPB with M .  extensor metacarpi radialis (EMR) most likely underwent parallel change in hummingbirds and swifts, while the distal tendon present only in hummingbirds changed from a thin sheet to a strong tendon. The combination of divergent (within hummingbirds or swifts) and parallel (between hummingbirds and swifts) evolutionary patterns implies that the taxonomic value of the propatagial complex in apodiformes depends on anatomical component and level of divergence. The congruence of anatomy with molecular phylogeny provides independent criteria for designating relatively ancestral versus derived clades of apodiformes. Based on these polarities, living hummingbirds and swifts express additional parallel trends from arboreal to more aerial foraging styles, and from depauperate to species-rich clades. Within apodiformes, the link of flight anatomy with taxonomic and ecologic diversity suggests that elaboration of locomotor modes was important for apodiform diversification, echoing a similar pattern for birds relative to their reptilian ancestors.  © 2002 The Linnean Society of London, Biological Journal of the Linnean Society , 2002, 77 , 211–219.     

Evolution of basal metabolic rate in bank voles from a multidirectional selection experiment

A major theme in evolutionary and ecological physiology of terrestrial vertebrates encompasses the factors underlying the evolution of endothermy in birds and mammals and interspecific variation of basal metabolic rate (BMR). Here, we applied the experimental evolution approach and compared BMR in lines of a wild rodent, the bank vole (Myodes glareolus), selected for 11 generations for: high swim-induced aerobic metabolism (A), ability to maintain body mass on a low-quality herbivorous diet (H) and intensity of predatory behaviour towards crickets (P). Four replicate lines were maintained for each of the selection directions and an unselected control (C). In comparison to C lines, A lines achieved a 49% higher maximum rate of oxygen consumption during swimming, H lines lost 1.3 g less mass in the test with low-quality diet and P lines attacked crickets five times more frequently. BMR was significantly higher in A lines than in C or H lines (60.8, 56.6 and 54.4 ml O₂ h⁻¹, respectively), and the values were intermediate in P lines (59.0 ml O₂ h⁻¹). Results of the selection experiment provide support for the hypothesis of a positive association between BMR and aerobic exercise performance, but not for the association of adaptation to herbivorous diet with either a high or low BMR.