ORCID Profile
0000-0002-4816-6005
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Publisher: Elsevier BV
Date: 03-2019
Publisher: The Company of Biologists
Date: 2014
DOI: 10.1242/JEB.098913
Abstract: Growth hormone (GH) transgenic Atlantic salmon display accelerated growth rates compared to non-transgenics. GH-transgenic fish also display cardiorespiratory and metabolic modifications that accompany the increased growth rate. An elevated routine metabolism has been described for pre- and post-smolt GH-transgenic salmon that also display improvements in oxygen delivery to support the increased aerobic demand. The early ontogenic effects of GH-transgenesis on the respiratory and cellular physiology of fish, especially during adverse environmental conditions and the effect of polyploidy, are unclear. Here, we investigated the effects of GH-transgenesis and polyploidy on metabolic, heart and ventilation rates and heat shock protein (HSP) levels, after exposure to acute hypoxia in post-hatch Atlantic salmon yolk-sac alevins. Metabolic rate decreased with decreasing partial pressures of oxygen in all genotypes. In normoxia, triploid transgenics displayed the highest mass specific metabolic rates in comparison to diploid transgenics and non-transgenic triploids, which in contrast had higher rates than diploid non-transgenics. In hypoxia, we observed a lower mass-specific metabolic rate in diploid non-transgenics compared to all other genotypes. However, no evidence for improved O2 uptake through heart or ventilation rate was found. Heart rate decreased in diploid non-transgenics while ventilation rate decreased in both diploid non-transgenics and triploid transgenics in severe hypoxia. Regardless of genotype or treatment, inducible HSP70 was not expressed in alevins. Following hypoxia, the constitutive isoform of HSP70, HSC70 decreased in transgenics and HSP90 expression decreased in all genotypes. These data suggest that physiological changes through GH-transgenesis and polyploidy are manifested during early ontogeny in Atlantic salmon.
Publisher: Elsevier BV
Date: 07-2008
DOI: 10.1016/J.BBABIO.2008.03.006
Abstract: Brown adipose tissue serves as a thermogenic organ in placental mammals to defend body temperature in the cold by nonshivering thermogenesis. The thermogenic function of brown adipose tissue is enabled by several specialised features on the organ as well as on the cellular level, including dense sympathetic innervation and vascularisation, high lipolytic capacity and mitochondrial density and the unique expression of uncoupling protein 1 (UCP1). This mitochondrial carrier protein is inserted into the inner mitochondrial membrane and stimulates maximum mitochondrial respiration by dissipating proton-motive force as heat. Studies in knockout mice have clearly demonstrated that UCP1 is essential for nonshivering thermogenesis in brown adipose tissue. For a long time it had been presumed that brown adipose tissue and UCP1 emerged in placental mammals providing them with a unique advantage to survive in the cold. Our subsequent discoveries of UCP1 orthologues in ectotherm vertebrates and marsupials clearly refute this presumption. We can now initiate comparative studies on the structure-function relationships in UCP1 orthologues from different vertebrates to elucidate when during vertebrate evolution UCP1 gained the biochemical properties required for nonshivering thermogenesis.
Publisher: Canadian Science Publishing
Date: 08-2016
Abstract: The maternal effect of fish egg size has profound implications for oxygen transfer across the egg shell surface, and therefore metabolism, especially under adverse environmental conditions like hypoxia. We found that metabolic rate ([Formula: see text]) of Atlantic salmon alevins was higher than of eggs in normoxia and hypoxia. Equally, the [Formula: see text] of smaller eggs from maiden spawners was lower than that of larger eggs from repeat spawners. Critical partial pressure of oxygen (PO 2 ) for hatching was lower in eggs from repeat spawners. Generally, the PO 2 within the egg capsule was lower for a given ambient PO 2 and decreased further with hypoxia, and the internal PO 2 was higher, the bigger the volume of the egg. Therefore, we conclude that the egg capsule poses a major barrier to oxygen exchange for the mature embryo that is more severe in eggs from maiden spawners than in eggs from repeat spawners. This was corroborated by a more advantageous egg surface area to [Formula: see text] ratio in eggs from repeat spawners. These findings challenge the “bigger is worse during incubation” hypothesis.
Publisher: Oxford University Press (OUP)
Date: 2020
Abstract: Predation risk can strongly shape prey ecological traits, with specific anti-predator responses displayed to reduce encounters with predators. Key environmental drivers, such as temperature, can profoundly modulate prey energetic costs in ectotherms, although we currently lack knowledge of how both temperature and predation risk can challenge prey physiology and ecology. Such uncertainties in predator–prey interactions are particularly relevant for marine regions experiencing rapid environmental changes due to climate change. Using the octopus (Octopus maorum)–spiny lobster (Jasus edwardsii) interaction as a predator–prey model, we examined different metabolic traits of sub adult spiny lobsters under predation risk in combination with two thermal scenarios: ‘current’ (20°C) and ‘warming’ (23°C), based on projections of sea-surface temperature under climate change. We examined lobster standard metabolic rates to define the energetic requirements at specific temperatures. Routine metabolic rates (RMRs) within a respirometer were used as a proxy of lobster activity during night and day time, and active metabolic rates, aerobic scope and excess post-exercise oxygen consumption were used to assess the energetic costs associated with escape responses (i.e. tail-flipping) in both thermal scenarios. Lobster standard metabolic rate increased at 23°C, suggesting an elevated energetic requirement (39%) compared to 20°C. Unthreatened lobsters displayed a strong circadian pattern in RMR with higher rates during the night compared with the day, which were strongly magnified at 23°C. Once exposed to predation risk, lobsters at 20°C quickly reduced their RMR by ~29%, suggesting an immobility or ‘freezing’ response to avoid predators. Conversely, lobsters acclimated to 23°C did not display such an anti-predator response. These findings suggest that warmer temperatures may induce a change to the typical immobility predation risk response of lobsters. It is hypothesized that heightened energetic maintenance requirements at higher temperatures may act to override the normal predator-risk responses under climate-change scenarios.
Publisher: Springer Science and Business Media LLC
Date: 15-04-2021
DOI: 10.1007/S00360-021-01362-0
Abstract: The thermogenic mechanisms supporting endothermy are still not fully understood in all major mammalian subgroups. In placental mammals, brown adipose tissue currently represents the most accepted source of adaptive non-shivering thermogenesis. Its mitochondrial protein UCP1 (uncoupling protein 1) catalyzes heat production, but the conservation of this mechanism is unclear in non-placental mammals and lost in some placentals. Here, we review the evidence for and against adaptive non-shivering thermogenesis in marsupials, which erged from placentals about 120–160 million years ago. We critically discuss potential mechanisms that may be involved in the heat-generating process among marsupials.
Publisher: Frontiers Media SA
Date: 12-07-2018
Publisher: Elsevier BV
Date: 11-2017
DOI: 10.1016/J.CBPA.2017.08.011
Abstract: Hypoxia is common in aquatic environments and has substantial effects on development, metabolism and survival of aquatic organisms. To understand the physiological effects of hypoxia and its dependence on temperature, metabolic rate ( [Formula: see text] ) and cardiorespiratory function were studied in response to acute hypoxia (21→5kPa) at different measurement temperatures (T
Publisher: Springer Science and Business Media LLC
Date: 16-10-2012
DOI: 10.1007/S00360-011-0623-X
Abstract: The presence of nonshivering thermogenesis in marsupials is controversially debated. Survival of small eutherian species in cold environments is crucially dependent on uncoupling protein 1 (UCP1)-mediated, adaptive nonshivering thermogenesis that is executed in brown adipose tissue. In a small dasyurid marsupial species, the fat-tailed dunnart (Sminthopsis crassicaudata), an orthologue of UCP1 has been recently identified which is upregulated during cold exposure resembling adaptive molecular adjustments of eutherian brown adipose tissue. Here, we tested for a thermogenic function of marsupial brown adipose tissue and UCP1 by evaluating the capacity of nonshivering thermogenesis in cold-acclimated dunnarts. In response to an optimal dosage of noradrenaline, cold-acclimated dunnarts (12°C) showed no additional recruitment of noradrenaline-induced maximal thermogenic capacity in comparison to warm-acclimated dunnarts (24°C). While no differences in body temperature were observed between the acclimation groups, basal metabolic rate was significantly elevated after cold acclimation. Therefore, we suggest that adaptive nonshivering thermogenesis does not occur in this marsupial species despite the cold recruitment of oxidative capacity and UCP1 in the interscapular fat deposit. In conclusion, the ancient UCP orthologue in marsupials does not contribute to the classical nonshivering thermogenesis, and may exhibit a different physiological role.
Publisher: Frontiers Media SA
Date: 25-07-2017
Publisher: Springer Science and Business Media LLC
Date: 31-08-2021
DOI: 10.1007/S00360-021-01401-W
Abstract: This collection of research articles was put together in honour of respiratory physiologist Professor Peter Frappell's (Frapps's) academic achievements. It encompasses various topics relating to the oxygen transport cascade, which was central to Frapps' career as a comparative physiologist. This issue highlights the ersity and outreach of his influence on the field and his pioneering spirit promoting novel perspectives, methodologies and research techniques. This issue also demonstrates how Frapps' knowledge and scientific findings answered some of the fundamental questions within the field of respiratory physiology while creating and fostering a rather unique work atmosphere in the laboratories he led. We thank Frapps for the contributions he has made and the friendships he has nurtured over his career. Cheers, Frapps - we love you mate!
Publisher: The Royal Society
Date: 06-2011
Abstract: Metabolic rates of mammals presumably increased during the evolution of endothermy, but molecular and cellular mechanisms underlying basal metabolic rate (BMR) are still not understood. It has been established that mitochondrial basal proton leak contributes significantly to BMR. Comparative studies among a ersity of eutherian mammals showed that BMR correlates with body mass and proton leak. Here, we studied BMR and mitochondrial basal proton leak in liver of various marsupial species. Surprisingly, we found that the mitochondrial proton leak was greater in marsupials than in eutherians, although marsupials have lower BMRs. To verify our finding, we kept similar-sized in iduals of a marsupial opossum ( Monodelphis domestica ) and a eutherian rodent ( Mesocricetus auratus ) species under identical conditions, and directly compared BMR and basal proton leak. We confirmed an approximately 40 per cent lower mass specific BMR in the opossum although its proton leak was significantly higher (approx. 60%). We demonstrate that the increase in BMR during eutherian evolution is not based on a general increase in the mitochondrial proton leak, although there is a similar allometric relationship of proton leak and BMR within mammalian groups. The difference in proton leak between endothermic groups may assist in elucidating distinct metabolic and habitat requirements that have evolved during mammalian ergence.
Publisher: Frontiers Media SA
Date: 22-06-2016
Publisher: Elsevier BV
Date: 08-2017
DOI: 10.1016/J.JTHERBIO.2017.01.013
Abstract: The mitochondrial basal proton leak (MBPL) significantly contributes to high body temperatures (T
Publisher: The Royal Society
Date: 26-09-2016
Abstract: While some migratory birds perform non-stop flights of over 11 000 km, many species only spend around 15% of the day in flight during migration, posing a question as to why flight times for many species are so short. Here, we test the idea that hyperthermia might constrain flight duration (FD) in a short-distance migrant using remote biologging technology to measure heart rate, hydrostatic pressure and body temperature in 19 migrating eider ducks ( Somateria mollissima ), a short-distance migrant. Our results reveal a stop-and-go migration strategy where migratory flights were frequent (14 flights day −1 ) and short (15.7 min), together with the fact that body temperature increases by 1°C, on average, during such flights, which equates to a rate of heat storage index (HSI) of 4°C h −1 . Furthermore, we could not find any evidence that short flights were limited by heart rate, together with the fact that the numerous stops could not be explained by the need to feed, as the frequency of es and the time spent feeding were comparatively small during the migratory period. We thus conclude that hyperthermia appears to be the predominant determinant of the observed migration strategy, and suggest that such a physiological limitation to FD may also occur in other species. This article is part of the themed issue ‘Moving in a moving medium: new perspectives on flight’.
Publisher: University of Chicago Press
Date: 09-2013
DOI: 10.1086/671800
Abstract: Polystyrene multiwell plates with integrated optodes act as multiple closed-system respirometers that enable the simultaneous measurement of oxygen consumption in small animals. However, the diffusion of oxygen through polystyrene needs to be taken into consideration. Here we provide an equation that accounts for the empirically determined rate of oxygen through a polystyrene well when calculating the instantaneous rate of oxygen consumption. Furthermore, we describe a novel method of calibrating a small respirometer for accuracy using micro-osmotic pumps containing an oxygen scavenger, which is delivered at a constant rate and therefore yields a constant rate of oxygen consumption in an airtight system.
Publisher: Frontiers Media SA
Date: 10-11-2017
Publisher: Springer Science and Business Media LLC
Date: 13-05-2015
DOI: 10.1007/S00360-015-0907-7
Abstract: In modern eutherian (placental) mammals, brown adipose tissue (BAT) evolved as a specialized thermogenic organ that is responsible for adaptive non-shivering thermogenesis (NST). For NST, energy metabolism of BAT mitochondria is increased by activation of uncoupling protein 1 (UCP1), which dissipates the proton motive force as heat. Despite the presence of UCP1 orthologues prior to the ergence of teleost fish and mammalian lineages, UCP1's significance for thermogenic adipose tissue emerged at later evolutionary stages. Recent studies on the presence of BAT in metatherians (marsupials) and eutherians of the afrotherian clade provide novel insights into the evolution of adaptive NST in mammals. In particular studies on the 'protoendothermic' lesser hedgehog tenrec (Afrotheria) suggest an evolutionary scenario linking BAT to the onset of eutherian endothermy. Here, we review the physiological function and distribution of BAT in an evolutionary context by focusing on the latest research on phylogenetically distinct species.
Location: Australia
No related grants have been discovered for Elias Theodor Polymeropoulos.