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Goh G, Vesterdorf K, Fuller A, Blache D, Maloney SK. Optimal sampling interval for characterisation of the circadian rhythm of body temperature in homeothermic animals using periodogram and cosinor analysis. Ecol Evol 2024; 14:e11243. [PMID: 38601852 PMCID: PMC11004550 DOI: 10.1002/ece3.11243] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2022] [Revised: 03/19/2024] [Accepted: 03/25/2024] [Indexed: 04/12/2024] Open
Abstract
Core body temperature (T c) is a critical aspect of homeostasis in birds and mammals and is increasingly used as a biomarker of the fitness of an animal to its environment. Periodogram and cosinor analysis can be used to estimate the characteristics of the circadian rhythm of T c from data obtained on loggers that have limited memory capacity and battery life. The sampling interval can be manipulated to maximise the recording period, but the impact of sampling interval on the output of periodogram or cosinor analysis is unknown. Some basic guidelines are available from signal analysis theory, but those guidelines have never been tested on T c data. We obtained data at 1-, 5- or 10-min intervals from nine avian or mammalian species, and re-sampled those data to simulate logging at up to 240-min intervals. The period of the rhythm was first analysed using the Lomb-Scargle periodogram, and the mesor, amplitude, acrophase and adjusted coefficient of determination (R 2) from the original and the re-sampled data were obtained using cosinor analysis. Sampling intervals longer than 60 min did not affect the average mesor, amplitude, acrophase or adjusted R 2, but did impact the estimation of the period of the rhythm. In most species, the period was not detectable when intervals longer than 120 min were used. In all individual profiles, a 30-min sampling interval modified the values of the mesor and amplitude by less than 0.1°C, and the adjusted R 2 by less than 0.1. At a 30-min interval, the acrophase was accurate to within 15 min for all species except mice. The adjusted R 2 increased as sampling frequency decreased. In most cases, a 30-min sampling interval provides a reliable estimate of the circadian T c rhythm using periodogram and cosinor analysis. Our findings will help biologists to select sampling intervals to fit their research goals.
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Affiliation(s)
- Grace Goh
- School of Human SciencesThe University of Western AustraliaCrawleyWestern AustraliaAustralia
| | - Kristine Vesterdorf
- School of Human SciencesThe University of Western AustraliaCrawleyWestern AustraliaAustralia
| | - Andrea Fuller
- Brain Function Research Group, School of Physiology, Faculty of Health SciencesUniversity of the WitwatersrandJohannesburgSouth Africa
| | - Dominique Blache
- School of Agriculture and EnvironmentThe University of Western AustraliaCrawleyWestern AustraliaAustralia
| | - Shane K. Maloney
- School of Human SciencesThe University of Western AustraliaCrawleyWestern AustraliaAustralia
- Brain Function Research Group, School of Physiology, Faculty of Health SciencesUniversity of the WitwatersrandJohannesburgSouth Africa
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Determining the different phases of torpor from skin- or body temperature data in heterotherms. J Therm Biol 2023; 111:103396. [PMID: 36585072 DOI: 10.1016/j.jtherbio.2022.103396] [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: 06/08/2022] [Revised: 10/28/2022] [Accepted: 11/22/2022] [Indexed: 11/27/2022]
Abstract
Technological innovations have made heat-sensitive data-loggers smaller, more efficient and less expensive, which has led to a growing body of literature that measures the skin- or body temperatures of small animals in their natural environments. Studies of this type on heterothermic endotherms have prompted much debate regarding how to best define 'torpor' expressions from skin- or body temperature data alone. We propose a new quantitative method for defining torpor 'entries', 'arousals' and 'stable torpor periods' whilst comparing the results to 'torpor bout' durations identified using only the torpor cut-off method. By decomposing a torpor bout into 'entries', 'stable torpor periods', and 'active arousals', we avoid biases introduced by using strict threshold temperature values for the onset of torpor, thereby allowing better insight into individual use of torpor. We present our method as an easy-to-use function written in R-code, offering an un-biased and consistent methodology to be applied on skin- or body temperature measurements across datasets and research groups. When testing the function on a large dataset of skin temperature data collected on three bat species in Norway (Plecotus auritus: Nind = 39; Eptesicus nilssonii: Nind = 11; Myotis brandtii: Nind = 10), we identified 461 complete torpor bouts across species. More than 40% of the torpor bouts (Nbouts = 192) did not contain stable torpor periods, because the bats aroused before they had reached a stable skin temperature level. Furthermore, only considering 'torpid' and 'euthermic' temperature values by applying strict cut-off thresholds led to potentially large underestimations of torpor bout durations compared to our quantitative determination of the onset and termination of each torpor bout. We highlight the importance of differentiating between torpor phases, especially for active arousals that can be very energetically expensive and may alter our evaluation of the actual energetic savings gained by an individual employing torpor.
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Grigg G, Nowack J, Bicudo JEPW, Bal NC, Woodward HN, Seymour RS. Whole-body endothermy: ancient, homologous and widespread among the ancestors of mammals, birds and crocodylians. Biol Rev Camb Philos Soc 2021; 97:766-801. [PMID: 34894040 PMCID: PMC9300183 DOI: 10.1111/brv.12822] [Citation(s) in RCA: 27] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2020] [Revised: 11/25/2021] [Accepted: 11/29/2021] [Indexed: 12/31/2022]
Abstract
The whole‐body (tachymetabolic) endothermy seen in modern birds and mammals is long held to have evolved independently in each group, a reasonable assumption when it was believed that its earliest appearances in birds and mammals arose many millions of years apart. That assumption is consistent with current acceptance that the non‐shivering thermogenesis (NST) component of regulatory body heat originates differently in each group: from skeletal muscle in birds and from brown adipose tissue (BAT) in mammals. However, BAT is absent in monotremes, marsupials, and many eutherians, all whole‐body endotherms. Indeed, recent research implies that BAT‐driven NST originated more recently and that the biochemical processes driving muscle NST in birds, many modern mammals and the ancestors of both may be similar, deriving from controlled ‘slippage’ of Ca2+ from the sarcoplasmic reticulum Ca2+‐ATPase (SERCA) in skeletal muscle, similar to a process seen in some fishes. This similarity prompted our realisation that the capacity for whole‐body endothermy could even have pre‐dated the divergence of Amniota into Synapsida and Sauropsida, leading us to hypothesise the homology of whole‐body endothermy in birds and mammals, in contrast to the current assumption of their independent (convergent) evolution. To explore the extent of similarity between muscle NST in mammals and birds we undertook a detailed review of these processes and their control in each group. We found considerable but not complete similarity between them: in extant mammals the ‘slippage’ is controlled by the protein sarcolipin (SLN), in birds the SLN is slightly different structurally and its role in NST is not yet proved. However, considering the multi‐millions of years since the separation of synapsids and diapsids, we consider that the similarity between NST production in birds and mammals is consistent with their whole‐body endothermy being homologous. If so, we should expect to find evidence for it much earlier and more widespread among extinct amniotes than is currently recognised. Accordingly, we conducted an extensive survey of the palaeontological literature using established proxies. Fossil bone histology reveals evidence of sustained rapid growth rates indicating tachymetabolism. Large body size and erect stature indicate high systemic arterial blood pressures and four‐chambered hearts, characteristic of tachymetabolism. Large nutrient foramina in long bones are indicative of high bone perfusion for rapid somatic growth and for repair of microfractures caused by intense locomotion. Obligate bipedality appeared early and only in whole‐body endotherms. Isotopic profiles of fossil material indicate endothermic levels of body temperature. These proxies led us to compelling evidence for the widespread occurrence of whole‐body endothermy among numerous extinct synapsids and sauropsids, and very early in each clade's family tree. These results are consistent with and support our hypothesis that tachymetabolic endothermy is plesiomorphic in Amniota. A hypothetical structure for the heart of the earliest endothermic amniotes is proposed. We conclude that there is strong evidence for whole‐body endothermy being ancient and widespread among amniotes and that the similarity of biochemical processes driving muscle NST in extant birds and mammals strengthens the case for its plesiomorphy.
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Affiliation(s)
- Gordon Grigg
- School of Biological Sciences, University of Queensland, Brisbane, QLD, 4072, Australia
| | - Julia Nowack
- School of Biological and Environmental Sciences, Liverpool John Moores University, James Parsons Building, Byrom Street, Liverpool, L3 3AF, U.K
| | | | | | - Holly N Woodward
- Oklahoma State University Center for Health Sciences, Tulsa, OK, 74107, U.S.A
| | - Roger S Seymour
- School of Biological Sciences, University of Adelaide, Adelaide, SA, 5005, Australia
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Abstract
In 1803, the French anatomist Étienne Geoffroy Saint-Hilaire decided that the newly described echidna and platypus should be placed in a separate order, the monotremes, intermediate between reptiles and mammals. The first physiological observations showed monotremes had low body temperatures and metabolic rates, and the consensus was that they were at a stage of physiological development intermediate between "higher mammals" and "lower vertebrates." Subsequent studies demonstrated that platypuses and echidnas are capable of close thermoregulation in the cold although less so under hot conditions. Because the short-beaked echidna Tachyglossus aculeatus, may show very large daily variations in body temperature, as well as seasonal hibernation, it has been suggested that it may provide a useful model of protoendotherm physiology. Such analysis is complicated by the very significant differences in thermal relations between echidnas from different climates. In all areas female echidnas regulate Tb within 1°C during egg incubation. The lactation period is considered to be the most energetically expensive time for most female mammals but lactating echidnas showed no measurable difference in field metabolic rate from non-lactating females, while the lactation period is more than 200 days for Kangaroo Island echidnas but only 150 days in Tasmania. In areas with mild winters echidnas show reduced activity and shallow torpor in autumn and early winter, but in areas with cold winters echidnas enter true hibernation with Tb falling as low as 4.5°C. Monotremes do not possess brown adipose tissue and maximum rates of rewarming from hibernation in echidnas were only half those of marmots of the same mass. Although echidnas show very large seasonal variations in fat stores associated with hibernation there is no relationship between plasma leptin and adiposity. Leptin levels are lowest during post-reproductive fattening, supporting suggestions that in evolutionary terms the anorectic effects of leptin preceded the adiposity signal. BMR of platypuses is twice that of echidnas although maximum metabolism is similar. High levels of thyroid hormones in platypuses may be driving metabolism limited by low body temperature. Monotremes show a mosaic of plesiomorphic and derived features but can still inform our understanding of the evolution of endothermy.
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Affiliation(s)
- Stewart C. Nicol
- Biological Sciences, University of TasmaniaHobart, TAS, Australia
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Stannard HJ, Bekkers JM, Old JM, McAllan BM, Shaw ME. Digestibility of a new diet for captive short-beaked echidnas (Tachyglossus aculeatus). Zoo Biol 2017; 36:56-61. [DOI: 10.1002/zoo.21347] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2016] [Revised: 12/05/2016] [Accepted: 12/13/2016] [Indexed: 11/08/2022]
Affiliation(s)
- Hayley J. Stannard
- School of Life and Environmental Sciences and Charles Perkins Centre; University of Sydney; Sydney New South Wales Australia
| | | | - Julie M. Old
- School of Science and Health; Western Sydney University; Richmond New South Wales Australia
| | - Bronwyn M. McAllan
- Discipline of Physiology; School of Medical Sciences and Bosch Institute; The University of Sydney; New South Wales Australia
| | - Michelle E. Shaw
- Taronga Wildlife Hospital; Taronga Conservation Society Australia; Mosman New South Wales Australia
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Morrow GE, Jones SM, Nicol SC. Interaction of hibernation and male reproductive function in wild Tasmanian echidnasTachyglossus aculeatus setosus. J Mammal 2016. [DOI: 10.1093/jmammal/gyw013] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
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Wallage A, Clarke L, Thomas L, Pyne M, Beard L, Ferguson A, Lisle A, Johnston S. Advances in the captive breeding and reproductive biology of the short-beaked echidna (Tachyglossus aculeatus). AUST J ZOOL 2015. [DOI: 10.1071/zo14069] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
Captive breeding of the short-beaked echidna (Tachyglossus aculeatus) has proven a difficult challenge; as recently as 2009, there were fewer than 10 echidnas born in captivity. We present observations of captive reproductive behaviour following video surveillance and measurements of body temperature collected from six captive female echidnas over a six-year period. In the first series of observations (2009–10) we examined the efficacy of artificial burrow boxes as possible aids for reproductive success. Females with access to burrow boxes had significantly higher levels of reproductive activity (P = 0.001), there was coincidental improvement in the production of eggs or pouch young (two eggs, one unhatched and one offspring). During 2009–10, a range of reproductive behaviours (courtship, copulation and postcopulation) were documented and analysed, as were new observations of oestrous cycle activity. Female body temperature was characteristically stable during egg incubation during this study and has the potential to be used as a tool for the assessment of reproductive status. Following initial observations, burrow boxes and infrared lamps were implemented as standard husbandry in our echidna breeding facility and the effects on reproductive success were monitored, albeit less intensively, for a further four years (2011–14). Although no direct causal effect could be ascribed, the use of burrow boxes and heat lamps coincided with a total of 13 young being born to four females in the last four years (2011–14). These female echidnas were found to be receptive at intervals throughout the breeding season, both before and after presumed incubation phases, suggesting that captive animals exhibit polyoestry. In 2012 and 2014, the same female showed evidence of producing two young from one breeding event.
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Nowack J, Mzilikazi N, Dausmann KH. Torpor as an emergency solution in Galago moholi: heterothermy is triggered by different constraints. J Comp Physiol B 2012; 183:547-56. [DOI: 10.1007/s00360-012-0725-0] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2012] [Revised: 10/17/2012] [Accepted: 11/22/2012] [Indexed: 10/27/2022]
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Morrow GE, Nicol SC. Maternal care in the Tasmanian echidna (Tachyglossus aculeatus setosus). AUST J ZOOL 2012. [DOI: 10.1071/zo12066] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
Parental care is central to the differences in reproductive behaviour and energy expenditure between males and females, and it is therefore crucial for understanding animal mating systems. We investigated post-gestation maternal care in a wild population of short-beaked echidnas (Tachyglossus aculeatus) in the Tasmanian midlands using a combination of external temperature loggers and motion-triggered infrared cameras. For the first few weeks of early lactation mothers do not leave their nursery burrow, which they keep at a stable and warm temperature, resulting in a greater rate of maternal mass loss during the period of maternal burrow confinement than during hibernation. However, after lactating mothers recommence feeding, they raise a young to ~1.5 kg on a diet of their milk while increasing their own body mass by a similar amount. Weaning in our population appears not to be abrupt as there is a period where young echidnas begin exploratory foraging while their mother is still lactating. After young are weaned and abandon the nursery burrow, there appear to be no further associations between mothers and young despite young echidnas remaining within their mother’s home range for the first 12 months of their life. Female echidnas time reproductive events with increases in ecosystem productivity, so that young are weaned at a time of maximum food abundance.
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Hampton M, Nelson BT, Andrews MT. Circulation and metabolic rates in a natural hibernator: an integrative physiological model. Am J Physiol Regul Integr Comp Physiol 2010; 299:R1478-88. [PMID: 20844258 PMCID: PMC3008751 DOI: 10.1152/ajpregu.00273.2010] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2010] [Accepted: 09/13/2010] [Indexed: 11/22/2022]
Abstract
Small hibernating mammals show regular oscillations in their heart rate and body temperature throughout the winter. Long periods of torpor are abruptly interrupted by arousals with heart rates that rapidly increase from 5 beats/min to over 400 beats/min and body temperatures that increase by ∼30°C only to drop back into the hypothermic torpid state within hours. Surgically implanted transmitters were used to obtain high-resolution electrocardiogram and body temperature data from hibernating thirteen-lined ground squirrels (Spermophilus tridecemlineatus). These data were used to construct a model of the circulatory system to gain greater understanding of these rapid and extreme changes in physiology. Our model provides estimates of metabolic rates during the torpor-arousal cycles in different model compartments that would be difficult to measure directly. In the compartment that models the more metabolically active tissues and organs (heart, brain, liver, and brown adipose tissue) the peak metabolic rate occurs at a core body temperature of 19°C approximately midway through an arousal. The peak metabolic rate of the active tissues is nine times the normothermic rate after the arousal is complete. For the overall metabolic rate in all tissues, the peak-to-resting ratio is five. This value is high for a rodent, which provides evidence for the hypothesis that the arousal from torpor is limited by the capabilities of the cardiovascular system.
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Affiliation(s)
- Marshall Hampton
- Department of Mathematics and Statistics, University of Minnesota Duluth, Duluth, Minnesota, USA.
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Meyer CW, Willershäuser M, Jastroch M, Rourke BC, Fromme T, Oelkrug R, Heldmaier G, Klingenspor M. Adaptive thermogenesis and thermal conductance in wild-type and UCP1-KO mice. Am J Physiol Regul Integr Comp Physiol 2010; 299:R1396-406. [PMID: 20826705 DOI: 10.1152/ajpregu.00021.2009] [Citation(s) in RCA: 116] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
We compared maximal cold-induced heat production (HPmax) and cold limits between warm (WA; 27°C), moderate cold (MCA; 18°C), or cold acclimated (CA; 5°C) wild-type and uncoupling-protein 1 knockout (UCP1-KO) mice. In wild-type mice, HPmax was successively increased after MCA and CA, and the cold limit was lowered to -8.3°C and -18.0°C, respectively. UCP1-KO mice also increased HPmax in response to MCA and CA, although to a lesser extent. Direct comparison revealed a maximal cold-induced recruitment of heat production by +473 mW and +227 mW in wild-type and UCP1-KO mice, respectively. The increase in cold tolerance of UCP1-KO mice from -0.9°C in MCA to -10.1°C in CA could not be directly related to changes in HPmax, indicating that UCP1-KO mice used the dissipated heat more efficiently than wild-type mice. As judged from respiratory quotients, acutely cold-challenged UCP1-KO mice showed a delayed transition toward lipid oxidation, and 5-h cold exposure revealed diminished physical activity and less variability in the control of metabolic rate. We conclude that BAT is required for maximal adaptive thermogenesis but also allows metabolic flexibility and a rapid switch toward sustained lipid-fuelled thermogenesis as an acute response to cold. In both CA groups, expression of contractile proteins (myosin heavy-chain isoforms) showed minor training effects in skeletal muscles, while cardiac muscle of UCP1-KO mice had novel expression of beta cardiac isoform. Neither respiration nor basal proton conductance of skeletal muscle mitochondria were different between genotypes. In subcutaneous white adipose tissue of UCP1-KO mice, cold exposure increased cytochrome-c oxidase activity and expression of the cell death-inducing DFFA-like effector A by 3.6-fold and 15-fold, respectively, indicating the recruitment of mitochondria-rich brown adipocyte-like cells. Absence of functional BAT leads to remodeling of white adipose tissue, which may significantly contribute to adaptive thermogenesis during cold acclimation.
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Affiliation(s)
- Carola W Meyer
- Dept. of Animal Physiology, Faculty of Biology, Philipps-Universität, Karl-von-Frisch Strasse 8, 35032 Marburg, Germany.
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Rial RV, Akaârir M, Gamundí A, Nicolau C, Garau C, Aparicio S, Tejada S, Gené L, González J, De Vera LM, Coenen AM, Barceló P, Esteban S. Evolution of wakefulness, sleep and hibernation: From reptiles to mammals. Neurosci Biobehav Rev 2010; 34:1144-60. [DOI: 10.1016/j.neubiorev.2010.01.008] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2009] [Revised: 01/08/2010] [Accepted: 01/19/2010] [Indexed: 11/17/2022]
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Morrow G, Nicol SC. Cool sex? Hibernation and reproduction overlap in the echidna. PLoS One 2009; 4:e6070. [PMID: 19562080 PMCID: PMC2699653 DOI: 10.1371/journal.pone.0006070] [Citation(s) in RCA: 56] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2009] [Accepted: 06/02/2009] [Indexed: 11/18/2022] Open
Abstract
During hibernation there is a slowing of all metabolic processes, and thus it is normally considered to be incompatible with reproduction. In Tasmania the egg-laying mammal, the echidna (Tachyglossus aculeatus) hibernates for several months before mating in mid-winter, and in previous studies we observed males with females that were still hibernating. We monitored the reproductive activity of radio-tracked echidnas by swabbing the reproductive tract for sperm while external temperature loggers provided information on the timing of hibernation. Additional information was provided by camera traps and ultrasound imaging. More than a third of the females found in mating groups were torpid, and the majority of these had mated. Some females re-entered deep torpor for extended periods after mating. Ultrasound examination showed a developing egg in the uterus of a female that had repeatedly re-entered torpor. The presence of fresh sperm in cloacal swabs taken from this female on three occasions after her presumed date of fertilization indicated she mated several times after being fertilized. The mating of males with torpid females is the result of extreme competition between promiscuous males, while re-entry into hibernation by pregnant females could improve the possibility of mating with a better quality male.
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Affiliation(s)
- Gemma Morrow
- School of Zoology, University of Tasmania, Hobart, Tasmania, Australia
| | - Stewart C. Nicol
- School of Zoology, University of Tasmania, Hobart, Tasmania, Australia
- * E-mail:
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Nicol SC, Andersen NA, Arnold W, Ruf T. Rewarming rates of two large hibernators: Comparison of a monotreme and a eutherian. J Therm Biol 2009. [DOI: 10.1016/j.jtherbio.2009.01.003] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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Owerkowicz T, Runciman S, Seymour RS. Russell V. Baudinette Memorial Symposium. Comp Biochem Physiol A Mol Integr Physiol 2008. [DOI: 10.1016/j.cbpa.2008.05.001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
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Nicol SC, Andersen NA. Cooling rates and body temperature regulation of hibernating echidnas (Tachyglossus aculeatus). ACTA ACUST UNITED AC 2007; 210:586-92. [PMID: 17267644 DOI: 10.1242/jeb.02701] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Echidnas (Tachyglossus aculeatus) are amongst the largest deep hibernators, but it is difficult to get them to hibernate normally under laboratory conditions. We measured body temperature (Tb) in 14 free-ranging echidnas using implanted data-loggers. Cooling during entry into hibernation bouts followed a Newtonian cooling curve, and conductances calculated from cooling curves were identical to those observed in cold exposed euthermic echidnas. Comparison with a reference soil temperature demonstrated that echidnas showed behavioural thermoregulation during hibernation; early in the hibernation season echidnas preferred to hibernate in cool areas, while during the coldest months they moved to warmer hibernacula, giving a preferred Tb in the range 8-10 degrees C. Thermal buffering against excessive variation in Tb may be as important as maintaining a low Tb.
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Affiliation(s)
- Stewart C Nicol
- School of Zoology, University of Tasmania, Private Bag 5, Hobart, Tasmania, 7001, Australia.
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