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Guagnoni IN, Armelin VA, da Silva Braga VH, Monteiro DA, Florindo LH. Cardiovascular responses and the role of the neurohumoral cardiac regulation during digestion in the herbivorous lizard Iguana iguana. J Exp Biol 2024; 227:jeb247105. [PMID: 38186316 DOI: 10.1242/jeb.247105] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2023] [Accepted: 12/27/2023] [Indexed: 01/09/2024]
Abstract
Carnivorous reptiles exhibit an intense metabolic increment during digestion, which is accompanied by several cardiovascular adjustments responsible for meeting the physiological demands of the gastrointestinal system. Postprandial tachycardia, a well-documented phenomenon in these animals, is mediated by the withdrawal of vagal tone associated with the chronotropic effects of non-adrenergic and non-cholinergic (NANC) factors. However, herbivorous reptiles exhibit a modest metabolic increment during digestion and there is no information about postprandial cardiovascular adjustments. Considering the significant impact of feeding characteristics on physiological responses, we investigated cardiovascular and metabolic responses, as well as the neurohumoral mechanisms of cardiac control, in the herbivorous lizard Iguana iguana during digestion. We measured oxygen consumption rate (O2), heart rate (fH), mean arterial blood pressure (MAP), myocardial activity, cardiac autonomic tone, fH/MAP variability and baroreflex efficiency in both fasting and digesting animals before and after parasympathetic blockade with atropine followed by double autonomic blockade with atropine and propranolol. Our results revealed that the peak of O2 in iguanas was reached 24 h after feeding, accompanied by an increase in myocardial activity and a subtle tachycardia mediated exclusively by a reduction in cardiac parasympathetic activity. This represents the first reported case of postprandial tachycardia in digesting reptiles without the involvement of NANC factors. Furthermore, this withdrawal of vagal stimulation during digestion may reduce the regulatory range for short-term fH adjustments, subsequently intensifying the blood pressure variability as a consequence of limiting baroreflex efficiency.
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Affiliation(s)
- Igor Noll Guagnoni
- Department of Biological Sciences, São Paulo State University (UNESP), Rua Cristóvão Colombo, 2265, São José do Rio Preto, SP 15054-000, Brazil
- National Institute of Science and Technology in Comparative Physiology (INCT - FAPESP/CNPq), São Paulo, SP 13506-900, Brazil
| | - Vinicius Araújo Armelin
- Department of Biological Sciences, São Paulo State University (UNESP), Rua Cristóvão Colombo, 2265, São José do Rio Preto, SP 15054-000, Brazil
- National Institute of Science and Technology in Comparative Physiology (INCT - FAPESP/CNPq), São Paulo, SP 13506-900, Brazil
- Department of Physiology, Institute of Biosciences (IB), University of São Paulo (USP), São Paulo, SP 05508-090, Brazil
| | - Victor Hugo da Silva Braga
- Department of Biological Sciences, São Paulo State University (UNESP), Rua Cristóvão Colombo, 2265, São José do Rio Preto, SP 15054-000, Brazil
- National Institute of Science and Technology in Comparative Physiology (INCT - FAPESP/CNPq), São Paulo, SP 13506-900, Brazil
| | - Diana Amaral Monteiro
- Department of Physiological Sciences, Federal University of São Carlos (UFSCar), Rodovia Washington Luiz, km 235, São Carlos, SP 13565-905, Brazil
| | - Luiz Henrique Florindo
- Department of Biological Sciences, São Paulo State University (UNESP), Rua Cristóvão Colombo, 2265, São José do Rio Preto, SP 15054-000, Brazil
- National Institute of Science and Technology in Comparative Physiology (INCT - FAPESP/CNPq), São Paulo, SP 13506-900, Brazil
- Department of Physiological Sciences, Federal University of São Carlos (UFSCar), Rodovia Washington Luiz, km 235, São Carlos, SP 13565-905, Brazil
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2
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da Cruz AL, Vilela B, Klein W. Morphological and physiological traits of the respiratory system in Iguana iguana and other non-avian reptiles. ZOOLOGY 2023; 157:126079. [PMID: 36868103 DOI: 10.1016/j.zool.2023.126079] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2022] [Revised: 02/08/2023] [Accepted: 02/18/2023] [Indexed: 02/23/2023]
Abstract
Functional morphology considers form and function to be intrinsically related. To understand organismal functions, a detailed knowledge of morphological and physiological traits is necessary. Regarding the respiratory system, the combined knowledge about pulmonary morphology and respiratory physiology is fundamental to understand how animals exchange gases and regulate critical functions to sustain metabolic activity. In the present study, the paucicameral lungs of Iguana iguana were analyzed morphometrically through stereological analysis using light and transmission electron images and compared with unicameral and multicameral lungs of six other non-avian reptiles. The morphological data were combined with physiological information to perform a principal component analysis (PCA) and phylogenetic tests of the relationship of the respiratory system. Iguana iguana, Lacerta viridis, and Salvator merianae presented similar pulmonary morphologies and physiologies when compared to Varanus examthematicus, Gekko gecko, Trachemys scripta, and Crocodylus niloticus. The former species showed an elevated respiratory surface area (%AR), a high diffusion capacity, a low volume of total parenchyma (VP), a low percentage of parenchyma concerning the lung volume (VL), and a higher surface/volume ratio of the parenchyma (SAR/VP), with high respiratory frequency (fR) and consequently total ventilation. The total parenchymal surface area (SA), effective parenchymal surface-to-volume ratio (SAR/VP), respiratory surface area (SAR), and anatomical diffusion factor (ADF) showed a phylogenetic signal, evidence that the morphological traits are more strongly correlated with the species' phylogeny than the physiological traits. In sum, our results indicated that the pulmonary morphology is intrinsically related to physiological traits of the respiratory system. Furthermore, phylogenetic signal tests also indicate that morphological traits are more likely to be evolutionary conserved than physiological traits, suggesting that evolutive physiological adaptations in the respiratory system could happen faster than morphological changes.
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Affiliation(s)
- André Luis da Cruz
- Institute of Biology, Federal University of Bahia, Rua Barão de Jeremoabo 147, Ondina, CEP 40170-115 Salvador, Bahia, Brazil.
| | - Bruno Vilela
- Institute of Biology, Federal University of Bahia, Rua Barão de Jeremoabo 147, Ondina, CEP 40170-115 Salvador, Bahia, Brazil.
| | - Wilfried Klein
- School of Philosophy, Sciences and Literature of Ribeirão Preto, University of São Paulo, Avenida Bandeirantes 3900. Monte Alegre, CEP 14040-900 Ribeirão Preto, São Paulo, Brazil.
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3
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Ibarrola I, Arranz K, Markaide P, Navarro E. Metabolic size scaling reflects growth performance effects on age-size relationships in mussels (Mytilus galloprovincialis). PLoS One 2022; 17:e0268053. [PMID: 36048874 PMCID: PMC9436149 DOI: 10.1371/journal.pone.0268053] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2022] [Accepted: 08/08/2022] [Indexed: 11/19/2022] Open
Abstract
Body-size scaling of metabolic rate in animals is typically allometric, with mass exponents that vary to reflect differences in the physiological status of organisms of both endogenous and environmental origin. Regarding the intraspecific analysis of this relationship in bivalve molluscs, one important source of metabolic variation comes from the large inter-individual differences in growth performance characteristic of this group. In the present study, we aimed to address the association of growth rate differences recorded among individual mussels (Mytilus galloprovincialis) with variable levels of the standard metabolic rate (SMR) resulting in growth-dependent shift in size scaling relationships. SMR was measured in mussels of different sizes and allometric functions fitting SMR vs. body-mass relationships were compared both inter- and intra-individually. The results revealed a metabolic component (the overhead of growth) attributable to the differential costs of maintenance of feeding and digestion structures between fast and slow growers; these costs were estimated to amount to a 3% increase in SMR per unit of increment in the weight specific growth rate. Scaling exponents computed for intraindividual SMR vs body-mass relationships had a common value b = 0.79 (~ ¾); however, when metabolic effects caused by differential growth were discounted, this value declined to 0.67 (= ⅔), characteristic of surface dependent processes. This last value of the scaling exponent was also recorded for the interindividual relationships of both standard and routine metabolic rates (SMR and RMR) after long-lasting maintenance of mussels under optimal uniform conditions in the laboratory. The above results were interpreted based on the metabolic level boundaries (MLB) hypothesis.
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Affiliation(s)
- Irrintzi Ibarrola
- Departamento de Genética, Antropología Física y Fisiología Animal, Facultad de Ciencia y Tecnología, Universidad del País Vasco/Euskal Herriko Unibertsitatea (UPV/EHU), Bilbao, Spain
| | - Kristina Arranz
- Departamento de Genética, Antropología Física y Fisiología Animal, Facultad de Ciencia y Tecnología, Universidad del País Vasco/Euskal Herriko Unibertsitatea (UPV/EHU), Bilbao, Spain
| | - Pablo Markaide
- Departamento de Genética, Antropología Física y Fisiología Animal, Facultad de Ciencia y Tecnología, Universidad del País Vasco/Euskal Herriko Unibertsitatea (UPV/EHU), Bilbao, Spain
| | - Enrique Navarro
- Departamento de Genética, Antropología Física y Fisiología Animal, Facultad de Ciencia y Tecnología, Universidad del País Vasco/Euskal Herriko Unibertsitatea (UPV/EHU), Bilbao, Spain
- * E-mail:
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4
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Norin T. Growth and Mortality as Causes of Variation in Metabolic Scaling Among Taxa and Taxonomic Levels. Integr Comp Biol 2022; 62:icac038. [PMID: 35580598 DOI: 10.1093/icb/icac038] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Metabolic rate (MR) usually changes (scales) out of proportion to body mass (BM) as MR = aBMb, where a is a normalisation constant and b is the scaling exponent that reflects how steep this change is. This scaling relationship is fundamental to biology, but over a century of research has provided little consensus on the value of b, and why it appears to vary among taxa and taxonomic levels. By analysing published data on fish and taking an individual-based approach to metabolic scaling, I show that variation in growth of fish under naturally restricted food availability can explain variation in within-individual (ontogenetic) b for standard (maintenance) metabolic rate (SMR) of brown trout (Salmo trutta), with the fastest growers having the steepest metabolic scaling (b ≈ 1). Moreover, I show that within-individual b can vary much more widely than previously assumed from work on different individuals or different species, from -1 to 1 for SMR among individual brown trout. The negative scaling of SMR for some individuals was caused by reductions in metabolic rate in a food limited environment, likely to maintain positive growth. This resulted in a mean within-individual b for SMR that was significantly lower than the across-individual ("static") b, a difference that also existed for another species, cunner (Tautogolabrus adspersus). Interestingly, the wide variation in ontogenetic b for SMR among individual brown trout did not exist for maximum (active) metabolic rate (MMR) of the same fish, showing that these two key metabolic traits (SMR and MMR) can scale independently of one another. I also show that across-species ("evolutionary") b for SMR of 134 fishes is significantly steeper (b approaching 1) than the mean ontogenetic b for the brown trout and cunner. Based on these interesting findings, I hypothesise that evolutionary and static metabolic scaling can be systematically different from ontogenetic scaling, and that the steeper evolutionary than ontogenetic scaling for fishes arises as a by-product of natural selection for fast-growing individuals with steep metabolic scaling (b ≈ 1) early in life, where size-selective mortality is high for fishes. I support this by showing that b for SMR tends to increase with natural mortality rates of fish larvae within taxa.
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Affiliation(s)
- Tommy Norin
- DTU Aqua: National Institute of Aquatic Resources, Technical University of Denmark, Kemitorvet, Building 202, 2800 Kgs. Lyngby, Denmark
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Ye X, Lu L, Jiang M, Jia J, Li W, Wu H, Liao Y, Li J. Metabolic scaling: individual versus intraspecific scaling of Nile tilapia (Oreochromis niloticus). J Comp Physiol B 2021; 191:721-729. [PMID: 33934186 DOI: 10.1007/s00360-021-01376-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2020] [Revised: 04/01/2021] [Accepted: 04/20/2021] [Indexed: 10/21/2022]
Abstract
We examined intraspecific scaling of the resting metabolic rate (RMR) of Nile tilapia (Oreochromis niloticus) under different culture conditions and further explored the allometric relationships between organ mass (heart, liver, brain, gills, viscera, and red muscles) and blood parameters (erythrocyte size and red blood cell counts) and body mass. Oreochromis niloticus were bred in individual and group cultures. The scaling exponent of the RMR in the individual cultures was b = 0.620-0.821 (n = 30) and that in the group culture was b = 0.770 [natural logarithm (ln) RMR = 0.770 ln M - 1.107 (n = 76)]. The results of the two experimental methods were similar and were not significantly different from 0.75 (3/4), as predicted by the metabolic theory of ecology. The active and inactive organs were scaled with body mass by an exponent of 0.940 and 1.012, respectively. There was no significant relationship between the blood parameters and body mass. These results suggest that the differences in the culture methods may not have affected the allometric scaling of O. niloticus metabolism. The proportion of active and inactive organs contributed to allometric changes in the metabolic rate with body mass. Red blood cells in fish are not generally representative, and cell size can only partially explain the allometric scaling of metabolism.
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Affiliation(s)
- Xiurong Ye
- Guangxi Key Laboratory of Beibu Gulf Marine Biodiversity Conservation, Ocean College, Beibu Gulf University, Qinzhou, China
| | - Lili Lu
- Guangxi Key Laboratory of Beibu Gulf Marine Biodiversity Conservation, Ocean College, Beibu Gulf University, Qinzhou, China
| | - Meijun Jiang
- Guangxi Key Laboratory of Beibu Gulf Marine Biodiversity Conservation, Ocean College, Beibu Gulf University, Qinzhou, China
| | - Jiuman Jia
- Guangxi Key Laboratory of Beibu Gulf Marine Biodiversity Conservation, Ocean College, Beibu Gulf University, Qinzhou, China
| | - Weifeng Li
- Guangxi Key Laboratory of Beibu Gulf Marine Biodiversity Conservation, Ocean College, Beibu Gulf University, Qinzhou, China
| | - Haiping Wu
- Guangxi Key Laboratory of Beibu Gulf Marine Biodiversity Conservation, Ocean College, Beibu Gulf University, Qinzhou, China
| | - Yongyan Liao
- Guangxi Key Laboratory of Beibu Gulf Marine Biodiversity Conservation, Ocean College, Beibu Gulf University, Qinzhou, China
| | - Jian Li
- Guangxi Key Laboratory of Beibu Gulf Marine Biodiversity Conservation, Ocean College, Beibu Gulf University, Qinzhou, China.
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6
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Kar F, Nakagawa S, Friesen CR, Noble DWA. Individual variation in thermal plasticity and its impact on mass‐scaling. OIKOS 2021. [DOI: 10.1111/oik.08122] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Affiliation(s)
- Fonti Kar
- School of Biological Earth and Environmental Sciences, Ecology and Evolution Research Centre, Univ. of New South Wales Sydney NSW Australia
| | - Shinichi Nakagawa
- School of Biological Earth and Environmental Sciences, Ecology and Evolution Research Centre, Univ. of New South Wales Sydney NSW Australia
- Diabetes and Metabolism Division, Garvan Inst. of Medical Research, Darlinghurst Sydney NSW Australia
| | - Christopher R. Friesen
- School of Earth, Atmospheric and Life Sciences, Faculty of Science, Medicine and Health, Univ. of Wollongong Wollongong NSW Australia
| | - Daniel W. A. Noble
- School of Biological Earth and Environmental Sciences, Ecology and Evolution Research Centre, Univ. of New South Wales Sydney NSW Australia
- Diabetes and Metabolism Division, Garvan Inst. of Medical Research, Darlinghurst Sydney NSW Australia
- Division of Ecology and Evolution, Research School of Biology, The Australian National Univ. Canberra ACT Australia
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7
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Norin T, Gamperl AK. Metabolic scaling of individuals vs. populations: Evidence for variation in scaling exponents at different hierarchical levels. Funct Ecol 2017. [DOI: 10.1111/1365-2435.12996] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Tommy Norin
- Department of Ocean SciencesMemorial University of Newfoundland St. John's NL Canada
| | - A. Kurt Gamperl
- Department of Ocean SciencesMemorial University of Newfoundland St. John's NL Canada
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Starostová Z, Konarzewski M, Kozłowski J, Kratochvíl L. Ontogeny of metabolic rate and red blood cell size in eyelid geckos: species follow different paths. PLoS One 2013; 8:e64715. [PMID: 23705003 PMCID: PMC3660393 DOI: 10.1371/journal.pone.0064715] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2012] [Accepted: 04/17/2013] [Indexed: 11/19/2022] Open
Abstract
While metabolism is a fundamental feature of all organisms, the causes of its scaling with body mass are not yet fully explained. Nevertheless, observations of negative correlations between red blood cell (RBC) size and the rate of metabolism suggest that size variation of these cells responsible for oxygen supply may play a crucial role in determining metabolic rate scaling in vertebrates. Based on a prediction derived from the Cell Metabolism Hypothesis, metabolic rate should increase linearly with body mass in species with RBC size invariance, and slower than linearly when RBC size increases with body mass. We found support for that prediction in five species of eyelid geckos (family Eublepharidae) with different patterns of RBC size variation during ontogenetic growth. During ontogeny, metabolic rate increases nearly linearly with body mass in those species of eyelid geckos where there is no correlation between RBC size and body mass, whereas non-linearity of metabolic rate scaling is evident in those species with ontogenetic increase of RBC size. Our findings provide evidence that ontogenetic variability in RBC size, possibly correlating with sizes of other cell types, could have important physiological consequences and can contribute to qualitatively different shape of the intraspecific relationship between metabolic rate and body mass.
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Affiliation(s)
- Zuzana Starostová
- Department of Zoology, Faculty of Science, Charles University in Prague, Prague, Czech Republic.
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9
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Estimation of climatic factors relating to occurrence of the maize orange leafhopper, Cicadulina bipunctata. POPUL ECOL 2012. [DOI: 10.1007/s10144-012-0320-y] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/28/2022]
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10
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Energetics in Liolaemini lizards: implications of a small body size and ecological conservatism. J Comp Physiol B 2010; 181:373-82. [DOI: 10.1007/s00360-010-0524-4] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2010] [Revised: 09/12/2010] [Accepted: 09/16/2010] [Indexed: 11/26/2022]
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11
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Abstract
When body size varies greatly, drug disposition can best be described as an allometric function of body weight. Therefore, the allometry of standard metabolic rate (SMR; 3/4 power) and body surface area (BSA; 2/3 power) have been advocated as surrogate markers for the prediction of key pharmacokinetic parameters. The goal of the present study was to examine the allometric basis of pharmacokinetic scaling within a species, green iguanas. Enrofloxacin was administered intravenously to 20 green iguanas (322-3824 g), and noncompartmental analysis was used to calculate standard pharmacokinetic parameters, which were log(10) transformed and regressed against log(10) body weight. The slopes of significant regressions were compared with the values of unity, 3/4, and 2/3. The slope of enrofloxacin total body clearance (Cl) was also compared with the slopes relating SMR and renal Cl of (99m)Tc-diethylenetriamine penta-acetic acid ((99m)DTPA) to body weight in iguanas. Enrofloxacin Cl depended allometrically on body weight with the power of 0.32. The slope of enrofloxacin Cl was significantly less than those of SMR, Cl of (99m)DTPA, and the 2/3 value. Therefore, the relationship between enrofloxacin Cl and body weight does not directly depend on the allometry of BSA, SMR, or renal Cl of (99m)DTPA in iguanas.
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Affiliation(s)
- L K Maxwell
- Department of Physiological Sciences, College of Veterinary Medicine, University of Florida, Gainesville, FL, USA.
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12
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Scantlebury M, Minting P. Differences in resting metabolic rates of two southern African tortoises:Psammobates oculiferusandGeochelone pardalis. AFR J HERPETOL 2006. [DOI: 10.1080/21564574.2006.9635547] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
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13
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Clusella Trullas S, Spotila JR, Paladino FV. Energetics during Hatchling Dispersal of the Olive Ridley TurtleLepidochelys olivaceaUsing Doubly Labeled Water. Physiol Biochem Zool 2006; 79:389-99. [PMID: 16555197 DOI: 10.1086/499982] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 05/27/2005] [Indexed: 11/03/2022]
Abstract
Studies of metabolism are central to the understanding of the ecology, behavior, and evolution of reptiles. This study focuses on one phase of the sea turtle life cycle, hatchling dispersal, and gives insight into energetic constraints that dispersal imposes on hatchlings. Hatchling dispersal is an energetically expensive phase in the life cycle of the olive ridley turtle Lepidochelys olivacea. Field metabolic rates (FMRs), determined using the doubly labeled water (DLW) method, for L. olivacea hatchlings digging out of their nest chamber, crawling at the sand surface, and swimming were five, four, and seven times, respectively, the resting metabolic rate (RMR). The cost of swimming was 1.5 and 1.8 times the cost of the digging and crawling phases, respectively, and we estimated that if L. olivacea hatchlings swim at frenzy levels, they can rely on yolk reserves to supply energy for only 3-6 d once they reach the ocean. We compared our RMR and FMR values by establishing an interspecific RMR mass-scaling relationship for a wide range of species in the order Testudines and found a scaling exponent of 1.06. This study demonstrates the feasibility of using the DLW method to estimate energetic costs of free-living sea turtle hatchlings and emphasizes the need for metabolic studies in various life-history stages.
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Affiliation(s)
- Susana Clusella Trullas
- Biology Department, Indiana University-Purdue University Fort Wayne, 2101 East Coliseum Boulevard, Fort Wayne, IN 46805, USA.
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14
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Glazier DS. Beyond the '3/4-power law': variation in the intra- and interspecific scaling of metabolic rate in animals. Biol Rev Camb Philos Soc 2006; 80:611-62. [PMID: 16221332 DOI: 10.1017/s1464793105006834] [Citation(s) in RCA: 599] [Impact Index Per Article: 33.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2003] [Revised: 05/27/2005] [Accepted: 06/08/2005] [Indexed: 01/01/2023]
Abstract
In this review I show that the '3/4-power scaling law' of metabolic rate is not universal, either within or among animal species. Significant variation in the scaling of metabolic rate with body mass is described mainly for animals, but also for unicells and plants. Much of this variation, which can be related to taxonomic, physiological, and/or environmental differences, is not adequately explained by existing theoretical models, which are also reviewed. As a result, synthetic explanatory schemes based on multiple boundary constraints and on the scaling of multiple energy-using processes are advocated. It is also stressed that a complete understanding of metabolic scaling will require the identification of both proximate (functional) and ultimate (evolutionary) causes. Four major types of intraspecific metabolic scaling with body mass are recognized [based on the power function R=aMb, where R is respiration (metabolic) rate, a is a constant, M is body mass, and b is the scaling exponent]: Type I: linear, negatively allometric (b<1); Type II: linear, isometric (b=1); Type III: nonlinear, ontogenetic shift from isometric (b=1), or nearly isometric, to negatively allometric (b<1); and Type IV: nonlinear, ontogenetic shift from positively allometric (b>1) to one or two later phases of negative allometry (b<1). Ontogenetic changes in the metabolic intensity of four component processes (i.e. growth, reproduction, locomotion, and heat production) appear to be important in these different patterns of metabolic scaling. These changes may, in turn, be shaped by age (size)-specific patterns of mortality. In addition, major differences in interspecific metabolic scaling are described, especially with respect to mode of temperature regulation, body-size range, and activity level. A 'metabolic-level boundaries hypothesis' focusing on two major constraints (surface-area limits on resource/waste exchange processes and mass/volume limits on power production) can explain much, but not all of this variation. My analysis indicates that further empirical and theoretical work is needed to understand fully the physiological and ecological bases for the considerable variation in metabolic scaling that is observed both within and among species. Recommended approaches for doing this are discussed. I conclude that the scaling of metabolism is not the simple result of a physical law, but rather appears to be the more complex result of diverse adaptations evolved in the context of both physico-chemical and ecological constraints.
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Affiliation(s)
- Douglas S Glazier
- Department of Biology, Juniata College, Huntingdon, Pennsylvania 16652, USA.
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15
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Seebacher F. A review of thermoregulation and physiological performance in reptiles: what is the role of phenotypic flexibility? J Comp Physiol B 2005; 175:453-61. [PMID: 16034580 DOI: 10.1007/s00360-005-0010-6] [Citation(s) in RCA: 94] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2005] [Revised: 04/29/2005] [Accepted: 05/24/2005] [Indexed: 10/25/2022]
Abstract
Biological functions are dependent on the temperature of the organism. Animals may respond to fluctuation in the thermal environment by regulating their body temperature and by modifying physiological and biochemical rates. Phenotypic flexibility (reversible phenotypic plasticity, acclimation, or acclimatisation in rate functions occurs in all major taxonomic groups and may be considered as an ancestral condition. Within the Reptilia, representatives from all major groups show phenotypic flexibility in response to long-term or chronic changes in the thermal environment. Acclimation or acclimatisation in reptiles are most commonly assessed by measuring whole animal responses such as oxygen consumption, but whole animal responses are comprised of variation in individual traits such as enzyme activities, hormone expression, and cardiovascular functions. The challenge now lies in connecting the changes in the components to the functioning of the whole animal and its fitness. Experimental designs in research on reptilian thermal physiology should incorporate the capacity for reversible phenotypic plasticity as a null-hypothesis, because the significance of differential body temperature-performance relationships (thermal reaction norms) between individuals, populations, or species cannot be assessed without testing that null-hypothesis.
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Affiliation(s)
- Frank Seebacher
- Integrative Physiology, School of Biological Sciences A08, The University of Sydney, NSW 2006, Australia.
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16
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Toe-Clipping Dramatically Reduces Clinging Performance in a Pad-Bearing Lizard (Anolis carolinensis). J HERPETOL 2005. [DOI: 10.1670/97-04n] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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17
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Suarez RK, Darveau CA, Childress JJ. Metabolic scaling: a many-splendoured thing. Comp Biochem Physiol B Biochem Mol Biol 2004; 139:531-41. [PMID: 15544974 DOI: 10.1016/j.cbpc.2004.05.001] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2004] [Revised: 04/26/2004] [Accepted: 05/05/2004] [Indexed: 11/21/2022]
Abstract
Animals at rest and during exercise display rates of aerobic metabolism, VO2, that represent mainly the sum of mitochondrial respiration rates in various organs. The relative contributions of these organs change with physiological state such that internal organs such as liver, kidney and brain account for most of the whole-body VO2 at rest, while locomotory muscles account for >90% of the maximum rate, VO2max, during maximal aerobic exercise. Mechanisms that regulate VO2 are complex and the relative importance of each step in a series, estimated by metabolic control analysis, depends upon the level of biological organization under consideration as well as physiological state. Despite this complexity, prominent single-cause models propose that metabolic rates are supply-limited and that the scaling of supply systems provides a sufficient explanation for the allometric scaling of metabolism. We argue that some assumptions, as well as current interpretations of the meaning (or consequences) of these constraints are flawed, i.e., elephants do not have lower mass-specific basal or maximal rates of aerobic metabolism because their mitochondria are more supply-limited than those of shrews. Animals do not violate the laws of physics, and the allometric scaling of supply systems would be expected, to some extent, to be matched by capacities for (and rates of) energy expenditure. But life is not so simple. Animals are so diverse that to do justice to metabolic scaling, it is also necessary to consider the scaling of energy expenditure. It is by doing so that models of metabolic scaling can be consistent with current paradigms in metabolic regulation and accommodate the range of inter- and intraspecific exponents found in nature. The "allometric cascade," a first attempt at such an accounting, was a source of great satisfaction to Peter Hochachka. It was the last door that he helped open to comparative physiologists before he said goodbye.
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Affiliation(s)
- Raul K Suarez
- Department of Ecology, Evolution and Marine Biology, University of California, Santa Barbara, CA 93106-9610, USA.
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Maxwell LK, Jacobson ER. Allometric scaling of kidney function in green iguanas. Comp Biochem Physiol A Mol Integr Physiol 2004; 138:383-90. [PMID: 15313494 DOI: 10.1016/j.cbpb.2004.05.011] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2004] [Revised: 05/24/2004] [Accepted: 05/25/2004] [Indexed: 11/25/2022]
Abstract
Numerous physiological parameters, such as metabolic rate and glomerular filtration rate (GFR), are allometrically related to body mass. Whereas the interspecific relationships between metabolic rate and body mass have been extensively studied in vertebrates, intraspecific studies of renal function have been limited. Therefore, kidney function was studied in 16 green iguanas, (Iguana iguana; 322-4764 g), by using nuclear scintigraphy to measure the renal uptake of 99mTc-diethylenetriamine pentaacetic acid (99mTc-DTPA), following either intravenous or intraosseous administration. Route of 99mTc-DTPA administration did not affect the percentage of the dose that accumulated in the kidney (P > 0.05). Renal uptake of 99mTc-DTPA was related to body mass (W, g) as: %Dose Kidney (min-1) = 11.09W(-0.235). Although not directly measured, the apparent renal clearance of 99mTc-DTPA could be described as: Renal CL 99mTc-DTPA (ml.min-1) = 0.005W(0.759), and the mass exponent did not differ from either the 2/3 or 3/4 values (P > 0.05). The similarity of the mass exponents relating both renal function and metabolic rate to body mass suggests a common mechanism underlying these allometric relationships. As this study also demonstrated that renal scintigraphy can be used to quantify kidney function in iguanas, this technique may be a useful research and diagnostic tool.
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Affiliation(s)
- Lara K Maxwell
- Department of Physiological Sciences, College of Veterinary Medicine, University of Florida, Gainesville, FL 32610, USA.
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