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      Patterns of activity and body temperature of Aldabra giant tortoises in relation to environmental temperature

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          Abstract

          We studied the temperature relations of wild and zoo Aldabra giant tortoises ( Aldabrachelys gigantea) focusing on (1) the relationship between environmental temperature and tortoise activity patterns ( n = 8 wild individuals) and (2) on tortoise body temperature fluctuations, including how their core and external body temperatures vary in relation to different environmental temperature ranges (seasons; n = 4 wild and n = 5 zoo individuals). In addition, we surveyed the literature to review the effect of body mass on core body temperature range in relation to environmental temperature in the Testudinidae. Diurnal activity of tortoises was bimodally distributed and influenced by environmental temperature and season. The mean air temperature at which activity is maximized was 27.9°C, with a range of 25.8–31.7°C. Furthermore, air temperature explained changes in the core body temperature better than did mass, and only during the coldest trial, did tortoises with higher mass show more stable temperatures. Our results, together with the overall Testudinidae overview, suggest that, once variation in environmental temperature has been taken into account, there is little effect of mass on the temperature stability of tortoises. Moreover, the presence of thermal inertia in an individual tortoise depends on the environmental temperatures, and we found no evidence for inertial homeothermy. Finally, patterns of core and external body temperatures in comparison with environmental temperatures suggest that Aldabra giant tortoises act as mixed conformer–regulators. Our study provides a baseline to manage the thermal environment of wild and rewilded populations of an important island ecosystem engineer species in an era of climate change.

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          Most cited references55

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          Integrating Thermal Physiology and Ecology of Ectotherms: A Discussion of Approaches

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            The evolution of endothermy and its diversity in mammals and birds.

            Many elements of mammalian and avian thermoregulatory mechanisms are present in reptiles, and the changes involved in the transition to endothermy are more quantitative than qualitative. Drawing on our experience with reptiles and echidnas, we comment on that transition and on current theories about how it occurred. The theories divide into two categories, depending on whether selection pressures operated directly or indirectly on mechanisms producing heat. Both categories of theories focus on explaining the evolution of homeothermic endothermy but ignore heterothermy. However, noting that hibernation and torpor are almost certainly plesiomorphic (=ancestral, primitive), and that heterothermy is very common among endotherms, we propose that homeothermic endothermy evolved via heterothermy, with the earliest protoendotherms being facultatively endothermic and retaining their ectothermic capacity for "constitutional eurythermy." Thus, unlike current models for the evolution of endothermy that assume that hibernation and torpor are specialisations arising from homeothermic ancestry, and therefore irrelevant, we consider that they are central. We note the sophistication of thermoregulatory behavior and control in reptiles, including precise control over conductance, and argue that brooding endothermy seen in some otherwise ectothermic Boidae suggests an incipient capacity for facultative endothermy in reptiles. We suggest that the earliest insulation in protoendotherms may have been internal, arising from redistribution of the fat bodies that are typical of reptiles. We note that short-beaked echidnas provide a useful living model of what an (advanced) protoendotherm may have been like. Echidnas have the advantages of endothermy, including the capacity for homeothermic endothermy during incubation, but are very relaxed in their thermoregulatory precision and minimise energetic costs by using ectothermy facultatively when entering short- or long-term torpor. They also have a substantial layer of internal dorsal insulation. We favor theories about the evolution of endothermy that invoke direct selection for the benefits conferred by warmth, such as expanding daily activity into the night, higher capacities for sustained activity, higher digestion rates, climatic range expansion, and, not unrelated, control over incubation temperature and the benefits for parental care. We present an indicative, stepwise schema in which observed patterns of body temperature are a consequence of selection pressures, the underlying mechanisms, and energy optimization, and in which homeothermy results when it is energetically desirable rather than as the logical endpoint.
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              Body Temperatures of Reptiles

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                Author and article information

                Contributors
                wilfredo.falcon@ieu.uzh.ch
                Journal
                Ecol Evol
                Ecol Evol
                10.1002/(ISSN)2045-7758
                ECE3
                Ecology and Evolution
                John Wiley and Sons Inc. (Hoboken )
                2045-7758
                19 January 2018
                February 2018
                : 8
                : 4 ( doiID: 10.1002/ece3.2018.8.issue-4 )
                : 2108-2121
                Affiliations
                [ 1 ] Department of Evolutionary Biology and Environmental Studies University of Zurich Zurich Switzerland
                [ 2 ] Zurich Zoo Zurich Switzerland
                [ 3 ] Clinic for Zoo Animals, Exotic Pets and Wildlife Vetsuisse Faculty University of Zurich Zurich Switzerland
                [ 4 ] Seychelles Islands Foundation PO Box 853, Mahe Seychelles
                Author notes
                [*] [* ] Correspondence

                Wilfredo Falcón, Department of Evolutionary Biology and Environmental Studies, University of Zurich, Zurich, Switzerland.

                Email: wilfredo.falcon@ 123456ieu.uzh.ch

                Author information
                http://orcid.org/0000-0003-2438-5681
                http://orcid.org/0000-0002-7043-7430
                http://orcid.org/0000-0002-4069-1884
                http://orcid.org/0000-0001-7477-2642
                http://orcid.org/0000-0003-3841-6207
                Article
                ECE33766
                10.1002/ece3.3766
                5817133
                29468029
                1d3d2e51-269f-4375-a619-e96a75322ba9
                © 2018 The Authors. Ecology and Evolution published by John Wiley & Sons Ltd.

                This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

                History
                : 08 June 2017
                : 19 October 2017
                : 06 December 2017
                Page count
                Figures: 7, Tables: 2, Pages: 14, Words: 10064
                Funding
                Funded by: Schweizerischer Nationalfonds zur Förderung der Wissenschaftlichen Forschung
                Award ID: 31003A_143940
                Categories
                Original Research
                Original Research
                Custom metadata
                2.0
                ece33766
                February 2018
                Converter:WILEY_ML3GV2_TO_NLMPMC version:version=5.3.2.2 mode:remove_FC converted:18.02.2018

                Evolutionary Biology
                aldabra,ectotherm,giant tortoise,testudinidae,thermoregulation
                Evolutionary Biology
                aldabra, ectotherm, giant tortoise, testudinidae, thermoregulation

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