Biomedical subjects

Roger S Seymour

Publications and source records attributed to Roger S Seymour.

At least 19 recordsLinked to original sources

PubMed2006

The role of thermogenesis in the pollination biology of the Amazon waterlily Victoria amazonica.

BACKGROUND AND AIMS: Several families of tropical plants have thermogenic flowers that show a 2-d protogynous sequence. Most are pollinated by large beetles that remain for the entire period in the flowers, where they compete for mates and feed. Active beetles require high body temperatures that they can achieve endogenously at great energy expense or attain passively and cheaply in a warm environment. Floral heating is therefore hypothesized to be a direct energy reward to endothermic beetles, in addition to its accepted role in enhancing scent production. METHODS: This study measures the pattern of floral heat production (as temperature in 20 flowers and respiration rates in five flowers) in Victoria amazonica at field sites in Guyana and correlates floral temperatures with body temperatures necessary for activity in visiting Cyclocephala hardyi beetles. KEY RESULTS: Thermogenesis occurred in a bimodal pattern, with peaks associated with the arrival and departure of beetles near sunset. Peak CO(2) production rates averaged 2.9 micromol s(-1), equivalent to a heat production of 1.4 W. Heat was generated mainly in the floral chamber on the first evening and by the stamen complex on the second. Mean chamber temperature remained between 29.3 and 34.7 degrees C during the first night, when ambient temperature was 23.5-25.2 degrees C. Beetles actively competed for mates and consumed stylar processes in the floral chamber, where their mean thoracic temperature was 33.2 degrees C. At the lower ambient temperatures outside of the flower, beetles capable of sustained flight had a similar mean temperature of 32.0 degrees C. CONCLUSIONS: Floral heating is not only associated with attraction, but continues throughout the night when beetles are active inside the flower and increases again when they leave. Floral chamber temperatures similar to activity temperatures of actively endothermic beetles imply that thermogenesis is an energy reward.

Guyana↗

PubMed2006

In situ measurement of calling metabolic rate in an Australian mole cricket, Gryllotalpa monanka.

Examination of the energetics of sound production usually requires measurement of species that will produce normal calls under unnatural circumstances. Such measurements are potentially compromised by stress-related changes in calling input (through a reduction in calling effort) or output (through forced use of sub-optimal singing burrows). To determine if such measurements are indeed affected by abstraction from a natural setting, we measured the energetics of song production in undisturbed mole crickets Gryllotalpa monanka and employed a new approach where the animal's singing chamber replaces the respirometry chamber normally used in studies of this type. It was therefore possible to measure metabolic rate (MR) of calling crickets in situ for animals within self-constructed burrows under natural conditions. Calling MR measured under these conditions averaged 13.5-fold higher than standard MR and 2.2-fold higher than MR measured during burrowing in the lab. The calling MR of G. monanka was similar to that measured for other calling insects, and to endothermic insects, but was only 10% of that allometrically predicted for a similarly sized insect (0.89 g) during flight. A male mole cricket is estimated to consume 5.9 ml of oxygen during construction of a calling burrow and a 1-h calling bout; by comparison, a flying female would consume a similar volume in less than 6 min.

Animals↗

PubMed2006

Non-invasive measurement of oxygen partial pressure, lateral diffusion and chorioallantoic blood flow under the avian eggshell.

We measured P(O2) under the shell of avian eggs indirectly, by sealing 0.05 mL glass tubes to the shell, sealing them with mercury and using an oxygen microelectrode to measure the contained gas that equilibrates with the gas in the shell membranes. This technique requires a smaller area of contact with the shell and a shorter equilibration period than established techniques, and allows measurements at several locations simultaneously and over a long period of time without endangering the embryo. P(O2) under the shell of chicken eggs decreased to 14.3 kPa on the day before hatching (day 19). P(O2) was unstable during late development and differences up to 3.1 kPa occurred transiently on opposite sides of the equator. By waxing the shell around sampling tubes, we estimated Krogh's coefficient for lateral oxygen diffusion in the shell membranes at 1.1 mmol cm(-1) d(-1) kPa(-1), a value about a third of a previous estimate. Sampling of gas under sufficiently large regions of waxed shell allowed indirect measurements of chorioallantoic venous P(O2), without affecting embryonic respiration. Venous P(O2) was 3.8 kPa on day 19. Assuming 14.3 kPa represents arterialized blood leaving the chorioallantois, it became possible to calculate the effective chorioallantoic blood flow rate, which was 3.5 mL min(-1) on day 19.

Animals↗

PubMed2006

Diving insects boost their buoyancy bubbles.

Backswimmers (Notonectidae) are common diving insects found around the world that exploit the mid-water zone for predation--they breathe by using an air bubble collected at the surface. Here we show that backswimmers achieve prolonged periods of neutral buoyancy by using oxygen stored in their haemoglobin to stabilize the volume of the bubble as they breathe from it. This enables them to maintain their position in the water column without continually swimming.

Air↗

PubMed2006

Development of maximum metabolic rate and pulmonary diffusing capacity in the superprecocial Australian Brush Turkey Alectura lathami: an allometric and morphometric study.

The Australian Brush Turkey Alectura lathami is a member of the Megapodiidae, the mound-building birds that produce totally independent, "superprecocial" hatchlings. This study examined the post-hatching development of resting and maximal metabolic rates, and the morphometrically determined changes in pulmonary gas exchange anatomy, in chicks during 3.7 months of growth from hatchlings (122 g) to subadults (1.1 kg). Allometric equations of the form y=aM(b) related gas exchange variables (y) to body mass (M, g). Metabolic rates were measured with open-flow respirometry (mL O2 min(-1)) of chicks resting in the dark and running above the aerobic limit on a treadmill. Resting metabolic rate (RMR=0.02 M(0.99)) and maximal metabolic rate (MMR=0.05 M(1.07)) scaled with exponents significantly above those of interspecific allometries of adult birds. However MMR was below that expected for other species of adult birds in flapping flight, consistent with the Brush Turkey's ground-dwelling habits. Total lung volumes (mL) increased faster than isometrically (V(L)=0.0075 M(1.19)), as did the surface area (cm(2)) of the blood-gas barrier (S(t)=7.80 M(1.23)), but the data overlapped those of adult species. Harmonic mean thickness of the blood-gas barrier was independent of body size (mean tau(ht),=0.39 microm) and was about twice that expected for flying birds. Diffusing capacity (mL O2 min(-1) kPa(-1)) of the blood-gas tissue barrier increased faster than isometrically (Dto2=0.049 M(1.23)); in hatchling Brush Turkeys, it was about 30% expected for adult birds, but this difference disappeared when they became subadults. When compared to altricial Australian pelicans that hatch at similar body masses, superprecocial Brush Turkeys had higher MMR and higher Dto2 at the same body size. A parallel allometry between MMR and Dto2 in Brush Turkeys and pelicans is consistent with the concept of symmorphosis during development.

Animals↗

PubMed2006

The scaling and temperature dependence of vertebrate metabolism.

Body size and temperature are primary determinants of metabolic rate, and the standard metabolic rate (SMR) of animals ranging in size from unicells to mammals has been thought to be proportional to body mass (M) raised to the power of three-quarters for over 40 years. However, recent evidence from rigorously selected datasets suggests that this is not the case for birds and mammals. To determine whether the influence of body mass on the metabolic rate of vertebrates is indeed universal, we compiled SMR measurements for 938 species spanning six orders of magnitude variation in mass. When normalized to a common temperature of 38 degrees C, the SMR scaling exponents of fish, amphibians, reptiles, birds and mammals are significantly heterogeneous. This suggests both that there is no universal metabolic allometry and that models that attempt to explain only quarter-power scaling of metabolic rate are unlikely to succeed.

Animals↗

PubMed2006

Contribution of the alternative pathway to respiration during thermogenesis in flowers of the sacred lotus.

We report results from in vivo measurements, using oxygen isotope discrimination techniques, of fluxes through the alternative and cytochrome respiratory pathways in thermogenic plant tissue, the floral receptacle of the sacred lotus (Nelumbo nucifera). Fluxes through both pathways were measured in thermoregulating flowers undergoing varying degrees of thermogenesis in response to ambient temperature. Significant increases in alternative pathway flux were found in lotus receptacles with temperatures 16 degrees C to 20 degrees C above ambient, but not in those with lesser amounts of heating. Alternative pathway flux in the hottest receptacles was 75% of the total respiratory flux. In contrast, fluxes through the cytochrome pathway did not change significantly during thermogenesis. These data support the hypothesis that increased flux through the alternative pathway is responsible for heating in the lotus and that it is unlikely that uncoupling proteins, which would have produced increased fluxes through the cytochrome pathway, contribute significantly to heating in this tissue. Comparisons of actual flux, with capacity determined using inhibitors, suggested that the alternative pathway was operating at close to maximum capacity in heating tissues of lotus. However, in nonheating tissues the inhibitor data significantly overestimated the alternative pathway flux. This confirms that isotopic measurements are necessary for accurate determination of fluxes through the two pathways.

Cytochromes↗

PubMed2006

Balancing the competing requirements of saltatorial and fossorial specialisation: burrowing costs in the spinifex hopping mouse, Notomys alexis.

Semi-fossorial animals (burrowing surface foragers) need to balance the competing morphological requirements of terrestrial and burrowing locomotion. These species rarely show the same degree of claw, forelimb and pectoral girdle structural development that fully fossorial forms (burrowing subterranean foragers) do, but nevertheless invest considerable amounts of energy in burrow systems. The compromise between terrestrial and burrowing locomotion was investigated by measuring net costs of burrowing and pedestrian transport in the spinifex hopping mouse, Notomys alexis, a species that forages in open areas in arid environments and is adapted for saltatorial locomotion. The net cost of transport by burrowing of hopping mice was found to be more expensive than for specialised fossorial species, and burrows were estimated to represent an energy investment equivalent to the terrestrial locomotion expected to be incurred in 17-100 days. A phylogenetically independent-contrasts approach revealed that morphological specialisation for burrowing was associated with low maximum running speeds in fossorial mammals and, for non-fossorial rodents and marsupials, maximum running speed was positively correlated with an index of habitat structure that ranged from arboreal to open desert. The high terrestrial speeds attainable by this semi-fossorial species by saltatory locomotion apparently outweigh the energetic savings that would be associated with burrowing specialisation.

Animals↗

PubMed2005

Sample size and mass range effects on the allometric exponent of basal metabolic rate.

The controversial relationship between body mass and basal metabolic rate in animals revolves around two questions: what is the allometric scaling exponent and what is the functional basis for it? For mammals, the first question could be resolved if measurements from all 4600 extant species were available, but this study shows that data for only 150 species, spanning three to four orders of magnitude variation in body mass, are sufficient to accurately determine the exponent. Because the currently available data set includes about 600 species that vary over five orders of magnitude in body size, further increases in sample size are unlikely to change the estimate of the scaling exponent.

Animals↗

PubMed2005

Allometric scaling of mammalian metabolism.

The importance of size as a determinant of metabolic rate (MR) was first suggested by Sarrus and Rameaux over 160 years ago. Max Rubner's finding of a proportionality between MR and body surface area in dogs (in 1883) was consistent with Sarrus and Rameaux's formulation and suggested a proportionality between MR and body mass (Mb) raised to the power of 2/3. However, interspecific analyses compiled during the first half of the 20th century concluded that mammalian basal MR (BMR, ml O2 h(-1)) was proportional to Mb3/4, a viewpoint that persisted for seven decades, even leading to its common application to non-mammalian groups. Beginning in 1997, the field was re-invigorated by three new theoretical explanations for 3/4-power BMR scaling. However, the debate over which theory accurately explains 3/4-power scaling may be premature, because some authors maintain that there is insufficient evidence to adopt an exponent of 3/4 over 2/3. If progress toward understanding the non-isometric scaling of BMR is ever to be made, it is first essential to know what the relationship actually is. We re-examine previous investigations of BMR scaling by standardising units and recalculating regression statistics. The proportion of large herbivores in a data set is positively correlated both with the scaling exponent (b, where BMR=aMb b) and the coefficient of variation (CV: the standard deviation of ln-ln residuals) of the relationship. Inclusion of large herbivores therefore both inflates b and increases variation around the calculated trendline. This is related to the long fast duration required to achieve the postabsorptive conditions required for determination of BMR, and because peak post-feeding resting MR (RMRpp) scales with an exponent of 0.75+/-0.03 (95% CI). Large herbivores are therefore less likely to be postabsorptive when MR is measured, and are likely to have a relatively high MR if not postabsorptive. The 3/4 power scaling of RMRpp is part of a wider trend where, with the notable exception of cold-induced maximum MR (b=0.65+/-0.05), b is positively correlated with the elevation of the relationship (higher MR values scale more steeply). Thus exercise-induced maximum MR (b=0.87+/-0.05) scales more steeply than RMRpp, field MR (b=0.73+/-0.04), thermoneutral resting MR (RMRt, b=0.712+/-0.013) and BMR. The implication of this observation is that contamination of BMR data with non-basal measurements is likely to increase the BMR scaling exponent even if the contamination is randomly distributed with respect to Mb. Artificially elevated scaling exponents can therefore be accounted for by the inclusion of measurements that fail to satisfy the requirements for basal metabolism, which are strictly defined (adult, non-reproductive, postabsorptive animals resting in a thermoneutral environment during the inactive circadian phase). Similarly, a positive correlation between Mb and body temperature (Tb) and between Tb and mass-independent BMR contributes to elevation of b. While not strictly a defined condition for the measurement of BMR, the normalisation of BMR measurements to a common Tb (36.2 degrees C) to achieve standard metabolic rate (SMR) further reduces the CV of the relationship. Clearly the value of the exponent depends on the conditions under which the data are selected. The exponent for true BMR is 0.686 (+/-0.014), Tb normalised SMR is 0.675 (+/-0.013) and RMRt is 0.712 (+/-0.013).

Animals↗

PubMed2004

Independent effects of heart-head distance and caudal blood pooling on blood pressure regulation in aquatic and terrestrial snakes.

Changes in orientation in a gravitational field markedly alter the patterns of blood pressure and flow in animals, especially tall or long ones such as giraffes or snakes. Vertical orientation tends to reduce blood flow and pressure in the head for two major reasons. First, the increased vertical blood column above the heart creates a gravitational hydrostatic pressure against which the heart must work. Second, expansion of dependent vessels in the lower extremities causes blood pooling and reduces return of venous blood to the heart, thereby lowering flow and pressure. For most animals, it is difficult to separate these two effects, but snakes offer the possibility of bending the animal in the region of the heart and manipulating the two ends of the body independently. We studied baroregulatory responses in terrestrial pythons (Liasis fuscus) and aquatic file snakes (Acrochordus arafurae) by tilting only the front or rear parts and then the whole animal. Changes in head blood pressure during partial tilts added up to the change during full tilt. The vertical distance to the head had twice as much influence on head blood pressure than did blood pooling in the pythons and four times as much in file snakes. This accounts for the cephalad location of the heart in terrestrial species compared with aquatic ones.

Animals↗

PubMed2004

Developmental allometry of pulmonary structure and function in the altricial Australian pelican Pelecanus conspicillatus.

Quantitative methods have been used to correlate maximal oxygen uptake with lung development in Australian pelicans. These birds produce the largest altricial neonates and become some of the largest birds capable of flight. During post-hatching growth to adults, body mass increases by two orders of magnitude (from 88 g to 8.8 kg). Oxygen consumption rates were measured at rest and during exposure to cold and during exercise. Then the lungs were quantitatively assessed using morphometric techniques. Allometric relationships between body mass (M) and gas exchange parameters (Y) were determined and evaluated by examining the exponents of the equation Y=aM(b). This intraspecific study was compared to interspecific studies of adult birds reported in the literature. Total lung volume scales similarly in juvenile pelicans (b=1.05) as in adult birds (b=1.02). However, surface area of the blood-gas barrier greatly increases (b=1.25), and its harmonic mean thickness does not significantly change (b=0.02), in comparison to exponents from adult birds (b=0.86 and 0.07, respectively). As a result, the diffusing capacity of the blood-gas tissue barrier increases much more during development (b=1.23) than it does in adult birds of different sizes (b=0.79). It increases in parallel to maximal oxygen consumption rate (b=1.28), suggesting that the gas exchange system is either limited by lung development or possibly symmorphic. The capacity of the oxygen delivery system is theoretically sufficient for powered flight well in advance of the bird's need to use it.

Analysis of Variance↗

PubMed2003

Environmental biology: heat reward for insect pollinators.

In neotropical forests, adults of many large scarab beetle species spend most of their time inside the floral chambers of heat-producing flowers, where they feed and mate throughout the night and rest during the following day, before briefly flying to another flower. Here we measure floral temperatures in Philodendron solimoesense (Araceae) in French Guiana and the respiration rates of Cyclocephala colasi beetles at floral and ambient temperatures, and show that the the beetles' extra energy requirements for activity are 2.0-4.8 times greater outside the flower than inside it. This finding indicates that heat produced by the flower constitutes an important energy reward to pollinators, allowing them to feed and mate at a fraction of the energy cost that would be required outside the flower.

Animals↗

PubMed2003

Mammalian basal metabolic rate is proportional to body mass2/3.

The relationship between mammalian basal metabolic rate (BMR, ml of O(2) per h) and body mass (M, g) has been the subject of regular investigation for over a century. Typically, the relationship is expressed as an allometric equation of the form BMR = aM(b). The scaling exponent (b) is a point of contention throughout this body of literature, within which arguments for and against geometric (b = 2/3) and quarter-power (b = 3/4) scaling are made and rebutted. Recently, interest in the topic has been revived by published explanations for quarter-power scaling based on fractal nutrient supply networks and four-dimensional biology. Here, a new analysis of the allometry of mammalian BMR that accounts for variation associated with body temperature, digestive state, and phylogeny finds no support for a metabolic scaling exponent of 3/4. Data encompassing five orders of magnitude variation in M and featuring 619 species from 19 mammalian orders show that BMR proportional, variant M(2/3).

Analysis of Variance↗

PubMed2003

Effect of local shell conductance on the vascularisation of the chicken chorioallantoic membrane.

The vascularisation of the chorioallantoic membrane (CAM) of avian embryos is influenced by environmental oxygen partial pressure (P(O(2))) on a global level: incubation at high P(O(2)) reduces the density of pre- and post-capillary vessels of the CAM and decelerates the thinning of the blood-gas barrier, and vice versa. This study investigates the effects of local P(O(2)) on vascular development during the formative period of days ten to fifteen, by making half of the egg hypoxic and the other half hyperoxic. The densities of arterioles, venules and capillaries were reduced under the hypoxic side, compared to untreated eggs, but not significantly changed on the hyperoxic side. Harmonic mean thickness of the tissue barrier and total CAM blood volume were not affected by the treatments. Vascular development of the CAM was therefore only partly influenced by local P(O(2)).

Adaptation, Physiological↗

PubMed2003

Ubiquitous expression of a gene encoding for uncoupling protein isolated from the thermogenic inflorescence of the dead horse arum Helicodiceros muscivorus.

Uncoupling proteins (UCPs) are a family of mitochondrial inner membrane proteins that have been implicated in heat production in mammalian cells. The inflorescences of several members of the arum lily family (Araceae) have also been shown to produce heat during flowering, but the involvement of UCP-mediated heat production in plants is not known. In this work a gene has been isolated termed HmUCPa that encodes for a putative uncoupling protein from Helicodiceros muscivorus, a highly thermogenic arum lily. RT-PCR analysis revealed that the expression of HmUCPa was ubiquitously found, both in thermogenic male florets and appendix, and the non-thermogenic female florets, spathe and club-shaped organs of the spadix. These results suggest that HmUCPa is not primarily involved in organ-specific heat production in H. muscivorus.

Arum↗

PubMed2002

Effect of regional changes to shell conductance on oxygen consumption and growth of chicken embryos.

Diffusive and perfusive gas conductances of the shell and chorioallantois of avian eggs are not homogeneous, leading to disequilibrium between the air cell gas and chorioallantoic venous blood. This study measured the embryonic ability to maintain oxygen consumption rate and growth under experimentally enhanced inhomogeneity of diffusive conductance, achieved by waxing half of the eggshell and exposing the other half to graded hyperoxia that doubled the oxygen gradient across the shell. Thus, the overall gas conductance was effectively normal but highly inhomogeneous. No differences were observed between the experimental and the control eggs in respiration, residual yolk or embryo growth rate from day 12 until day 20. The embryo was able to utilise the increase of oxygen in the environment to compensate for the loss of about half of its respiratory surface area under the wax. The results indicate that an even distribution of pores in the eggshell and uniformity of chorioallantoic perfusion are not required for successful avian development.

Animals↗

PubMed2002

Respiration and energetics of embryonic development in a large altricial bird, the Australian pelican (Pelecanus conspicillatus).

We examined whether the previously reported low cost of embryonic development in pelicans could be attributed to a more efficient conversion of egg energy to hatchling tissues as a result of high initial egg water content, low embryonic metabolic rate and growth later in incubation than in more precocious species. We therefore determined egg and hatchling composition and the development of embryonic respiration in the Australian pelican Pelecanus conspicillatus, which lays one of the largest eggs (140-210 g) with an altricial developmental mode. The small yolk fraction (21%) is typical of all pelecaniforms; however, we found that intraspecific variability in fresh egg mass was related to water content (principally in the albumen), but independent of yolk mass (mean 13 g dry mass). P. conspicillatus eggs have, on average, 635 kJ of energy, irrespective of egg mass across the whole range of egg mass. The embryonic developmental pattern of O(2) consumption and CO(2) production showed clear plateaus lasting 2-3 days immediately prior to internal pipping, resembling the typical precocial pattern. However, the rate of pre-internal pipping O(2) consumption was low in comparison with that of precocial species of similar egg mass. There is no evidence to support the hypothesis that the observed plateau in rates of O(2) uptake is due to a diffusion limitation of the eggshell gas conductance in this species. Embryonic metabolic rate nearly doubled during the pipping period, but the mass-independent metabolic rate of the hatchling was low in comparison with that of the resting adult. The total O(2) consumed (11 063 ml) is equivalent to 217.3 kJ (or 34% of egg energy) based on indirect calorimetry and the observed respiratory exchange ratio of 0.71. Thus, the cost of development (direct calorimetry) was 0.29 kJ J(-1) in the egg (mean egg mass 168 g), which is one of lowest reported values. As a result, the production efficiency of pelican embryonic development was 61.6%, higher than the average for birds in general (56.9%) and, in particular, of seabirds that have prolonged incubation periods on the basis of egg mass. High efficiency in embryonic development in this species was attained as a result of rapid embryonic growth later in incubation, low hatchling energy density (23.6 kJ g(-1) dry matter) and dry matter content, low embryonic metabolic rate throughout incubation and a shorter than expected incubation period of 33 days (predicted 36 days).

Animals↗