Wednesday, July 25, 2007

Hibernation, Aging and Longevity


I would greatly appreciate an advice from knowledgeable people on the effects of lethargic sleep on human aging and longevity. I have tried to search for scientific literature on this topic, but found mostly studies on the effects of hibernation in animal models (see below, listed in reversed chronological order).

If you know more direct studies and publications on this topic (effects of lethargic sleep on human aging and longevity), please advise by posting a comment here (see the end of this post for comment option).

Thank you!

Selected list of scientific publications on the effects of Lethargic Sleep (Hibernation) on Aging and Longevity

: A skeletochronological study of age, growth and longevity in a population of the frog Rana ridibunda from southern Europe.
Zoology (Jena). 2007 Jul 10; [Epub ahead of print]
Kyriakopoulou-Sklavounou P, Stylianou P, Tsiora A.
Department of Zoology, Aristotle University of Thessaloniki, Box 134, 541 24 Thessaloniki, Greece.
Age at sexual maturity and longevity in a population of Rana ridibunda from north-eastern Greece were studied by skeletochronology performed on the phalanges. Analysis of the age structure was based on counting the lines of arrested growth (LAGs). Sexual maturity for both sexes arises during the first year or after the first hibernation. Ages ranged from 1 to 5 years (mean=2.96) among 52 males and from 1 to 5 years (mean=3.73) among 56 females. The mean snout-vent length was 69.03+/-12.6mm in males and 82.38+/-13.27mm in females. The difference between the sexes in age and size was significant. Growth of individuals was fitted on The von Bertalanffy model. The growth coefficient (K) was 0.57 in males and 0.54 in females, mainly due to faster male growth between metamorphosis and maturation.
PMID: 17628458

2: Black bear femoral geometry and cortical porosity are not adversely affected by ageing despite annual periods of disuse (hibernation).
J Anat. 2007 Feb;210(2):160-9.
McGee ME, Miller DL, Auger J, Black HL, Donahue SW.
Department of Biomedical Engineering, Michigan Technological University, Houghton, MI 49931,USA.
Disuse (i.e. inactivity) causes bone loss, and a recovery period that is 2-3 times longer than the inactive period is usually required to recover lost bone. However, black bears experience annual disuse (hibernation) and remobilization periods that are approximately equal in length, yet bears maintain or increase cortical bone material properties and whole bone mechanical properties with age. In this study, we investigated the architectural properties of bear femurs to determine whether cortical structure is preserved with age in bears. We showed that cross-sectional geometric properties increase with age, but porosity and resorption cavity density do not change with age in skeletally immature male and female bears. These findings suggest that structural properties substantially contribute to increasing whole bone strength with age in bears, particularly during skeletal maturation. Porosity was not different between skeletally immature and mature bears, and showed minimal regional variations between anatomical quadrants and radial positions that were similar in pattern and magnitude between skeletally immature and mature bears. We also found gender dimorphisms in bear cortical bone properties: females have smaller, less porous bones than males. Our results provide further support for the idea that black bears possess a biological mechanism to prevent disuse osteoporosis.
PMID: 17261138

3: Of bears, frogs, meat, mice and men: complexity of factors affecting skeletal muscle mass and fat.
Bioessays. 2006 Oct;28(10):994-1009. Review.
Shavlakadze T, Grounds M.
School of Anatomy and Human Biology, The University of Western Australia, 6009, Western Australia.
Extreme loss of skeletal muscle mass (atrophy) occurs in human muscles that are not used. In striking contrast, skeletal muscles do not rapidly waste away in hibernating mammals such as bears, or aestivating frogs, subjected to many months of inactivity and starvation. What factors regulate skeletal muscle mass and what mechanisms protect against muscle atrophy in some species? Severe atrophy also occurs with ageing and there is much clinical interest in reducing such loss of muscle mass and strength (sarcopenia). In the meat industry, a key aim is optimizing the control of skeletal muscle growth and meat quality. The impaired response of muscle to insulin resulting in diabetes, that is a consequence of the metabolic impact of increasing obesity and fat deposition in humans, is also of increasing clinical concern. Intensive research in these fields, combined with mouse models, is reviewed with respect to the molecular control of muscle growth (myogenesis) and atrophy/hypertrophy and fat deposition (adipogenesis) in skeletal muscle, with a focus on IGF-1/insulin signaling. (c) 2006 Wiley Periodicals, Inc.
PMID: 16998828

4: [Chrological and physiological age of the tick Ixodes ricinus females]
Parazitologiia. 2006 Mar-Apr;40(2):132-9. Russian.
Naumov RL.
Changes of the physiological age in 3 groups of the laboratory reared Ixodes ricinus females were investigated over the period of 6-16 months. The longevity was studied in 27 groups of the tick females from a wild population during 2 seasons of the tick activity. Physiological age of the tick females was determined at the beginning of the study and then monthly till the end of the study. It was established that physiological ageing takes place during the life of the tick, and the ageing of different females is carried out non-uniformly. Physiologically young females (of the second physiological age) in the groups of laboratory reared ticks were occurred right up to 11th month after molting (including 4 months of hibernation in a refrigerator). Ticks of the second physiological age were occurred in the groups from wild populations after one or two periods of hibernation. Hence, in natural conditions some females may be physiologically young both in the first and second seasons of the ticks' activity. On the other hand, physiologically old tick females (of the 4th physiological age) appeared in the groups in a month after molting. The supposition is proposed that the tick population is heterogeneous by the rate of the individual ageing. It means that different specimens differ by the rate of consumption of their storage compounds i.e. by the intensity of metabolism. Such difference may be a cause of the variability in chemical conditions in the gut of the tick being the habitat of Borrelia.
PMID: 16755722

5: Food, fertility and longevity.
Biogerontology. 2006 Jun;7(3):139-41.
Holliday R.
Some animals live in environments in which the food supply fluctuates. When it is scarce these animals do not breed, but invest resources into survival until food is again available, and they can reproduce. Under these circumstances the lifespan can be increased, just as it is after calorie restriction. Other animals have a fairly constant food supply, and it is predicted that these would not have an extended life span if subjected to calorie restriction. Hibernation is a natural form of calorie restriction, and in some cases may lengthen lifespan
PMID: 16676135

6: Parathyroid hormone may maintain bone formation in hibernating black bears (Ursus americanus) to prevent disuse osteoporosis.
J Exp Biol. 2006 May;209(Pt 9):1630-8.
Donahue SW, Galley SA, Vaughan MR, Patterson-Buckendahl P, Demers LM, Vance JL, McGee ME.
Michigan Technological University, 1400 Townsend Drive, Houghton, 49931, USA.
Mechanical unloading of bone causes an imbalance in bone formation and resorption leading to bone loss and increased fracture risk. Black bears (Ursus americanus) are inactive for up to six months during hibernation, yet bone mineral content and strength do not decrease with disuse or aging. To test whether hibernating bears have biological mechanisms to prevent disuse osteoporosis, we measured the serum concentrations of hormones and growth factors involved in bone metabolism and correlated them with the serum concentration of a bone formation marker (osteocalcin). Serum was obtained from black bears over a 7-month duration that included periods of activity and inactivity. Both resorption and formation markers increased during hibernation, suggesting high bone turnover occurred during inactivity. However, bone formation appeared to be balanced with bone resorption. The serum concentration of parathyroid hormone (PTH) was higher in the hibernation (P=0.35) and post-hibernation (P=0.006) seasons relative to pre-hibernation levels. Serum leptin was lower (P<0.004) p="0.64)">

7: Hibernating bears as a model for preventing disuse osteoporosis.
J Biomech. 2006;39(8):1480-8. Epub 2005 Jun 21.
Donahue SW, McGee ME, Harvey KB, Vaughan MR, Robbins CT.
Department of Biomedical Engineering, Michigan Technological University, 309 Minerals and Materials Engineering Building, 1400 Townsend Drive, Houghton, MI 49931, USA.
The hibernating bear is an excellent model for disuse osteoporosis in humans because it is a naturally occurring large animal model. Furthermore, bears and humans have similar lower limb skeletal morphology, and bears walk plantigrade like humans. Black bears (Ursus americanus) may not develop disuse osteoporosis during long periods of disuse (i.e. hibernation) because they maintain osteoblastic bone formation during hibernation. As a consequence, bone volume, mineral content, porosity, and strength are not adversely affected by annual periods of disuse. In fact, cortical bone bending strength has been shown to increase with age in hibernating black bears without a significant change in porosity. Other animals require remobilization periods 2-3 times longer than the immobilization period to recover the bone lost during disuse. Our findings support the hypothesis that black bears, which hibernate for as long as 5-7 months annually, have evolved biological mechanisms to mitigate the adverse effects of disuse on bone porosity and strength.
PMID: 15975583

8: The myth and reality of reversal of aging by hormesis.
Ann N Y Acad Sci. 2005 Dec;1057:165-76.
Sonneborn JS.
Department of Zoology & Physiology, University of Wyoming, Box 3663, 16th & Gibbon Street, Laramie, Wyoming 82071, USA.
Hormesis is an adaptive response to low doses of otherwise harmful agents by triggering a cascade of stress-specific resistance pathways. Evidence from protozoa, nematodes, flies, rodents, and primates indicate that stress-induced tolerance modulates survival and longevity. "Reality" is that hormesis can prolong the healthy life span. Genetic background provides the potential for longevity duration induced by stress. Senesence, or aging, is generally thought to be due to a different impact of selection for alleles positive for reproduction during early life but harmful in later life, a process called antagonistic pleiotropy (multiple phenotypic changes by a single gene). After reproduction, life span is "invisible" to selection. I propose the revision that mutations selected for survival until reproduction in early life may also extend later life (protagonistic pleiotropy). The protagonist candidate genes for extended life span are hormetic response genes, which activate the protective effect in both early and later life. My revision of the earlier evolutionary theory implies that natural selection of genes critical for early survival (life span until reproduction) can also be beneficial for extended longevity in old age, tipping the evolutionary balance in favor of a latent inducible life span extension unless excess stressor challenge exceeds the protection capacity. Mimetic triggers of the stress response promise the option of tricking the induction of metabolic pathways that confer resistance to environmental challenges, increased healthy life span, rejuvenation, and disease intervention without the danger of overwhelming damage by the stressor. Public policy should anticipate an increase in healthy life span.
PMID: 16399893

9: The tensile strength of black bear (Ursus americanus) cortical bone is not compromised with aging despite annual periods of hibernation.
J Biomech. 2005 Nov;38(11):2143-50.
Harvey KB, Drummer TD, Donahue SW.
Department of Mechanical Engineering-Engineering Mechanics, Michigan Technological University, 1400 Townsend Drive, Houghton, MI 49931, USA.
Black bears (Ursus americanus) may not develop disuse osteoporosis during long periods of disuse (i.e. hibernation) because they may be able to maintain bone formation. Previously, we found that cortical bone bending strength was not compromised with age in black bears' tibias, despite annual periods of disuse. Here we showed that cortical bone tensile strength (166-198MPa) also does not decrease with age (2-14 years) in black bear tibias. There were also no significant age-related changes in cortical bone porosity in black bear tibias. It is likely that the ability of black bears to maintain bone formation during hibernation keeps bone porosity low (2.3-8.6%) with aging, notwithstanding annual periods of disuse. This low porosity likely preserves ultimate stress with aging. Female bears give birth and nurse during hibernation; however, we found no significant differences between male and female tensile material properties, mineral content, or porosity. Our findings support the idea that black bears, which hibernate 5-7 months annually, have evolved biological mechanisms to mitigate the adverse effects of disuse on bone porosity and strength.
PMID: 16115638

10: Phosphorylation of the tau protein sequence 199-205 in the hippocampal CA3 region of Syrian hamsters in adulthood and during aging.
Brain Res. 2005 Sep 14;1056(1):100-4.
Hartig W, Oklejewicz M, Strijkstra AM, Boerema AS, Stieler J, Arendt T.
Department of Neurochemistry, Paul Flechsig Institute for Brain Research, University of Leipzig, Jahnallee 59, D-04109 Leipzig, Germany.
Paired helical filaments formed by the abnormally phosphorylated microtubule-associated tau are a main sign of Alzheimer's disease and other neurodegenerative disorders. The hippocampal CA3 region, a brain region with a high degree of synaptic plasticity, is known to be strongly involved in tau hyperphosphorylation in several neurodegenerative diseases. In addition, reversible tau phosphorylation was observed during hibernation in European ground squirrels. The present study provides data on the tau phosphorylation status in the hippocampus of euthermic Syrian hamsters (Mesocricetus auratus), laboratory animals potentially prone to hibernation. Mossy fibers in the CA3 region of all investigated hamsters were immunostained using an antiserum detecting phospho-serine 199 of tau. A similar staining pattern was obtained with CP-13 detecting phospho-serine 202. In contrast, the monoclonal antibody AT8, recognizing both phosphorylated serine 202 and threonine 205, stained the CA3 region only in old hamsters. These findings implicate an additional link between aging, tau phosphorylation and synaptic plasticity. Furthermore, the presented data allow analyses whether tau phosphorylation is reversible in these facultative hibernators and versatile laboratory animal as it was recently shown for the hibernation cycle of European ground squirrels.
PMID: 16095576 [PubMed - indexed for MEDLINE]

11: Sperm influences female hibernation success, survival and fitness in the bumble-bee Bombus terrestris.
Proc Biol Sci. 2005 Feb 7;272(1560):319-23.
Baer B, Schmid-Hempel P.
Copenhagen University, Institute of Biology, Department for Population Biology, 2100 Copenhagen, Denmark.
We present evidence that in the absence of the transfer of male gland compounds in the ejaculate as well as of behavioural male traits, such as mate guarding or harming of females, sperm itself affects female life-history traits such as hibernation success, female longevity and female fitness. Using the bumble-bee Bombus terrestris, we artificially inseminated queens (females) with sperm from one or several males and show that sire groups (groups of brother males) vary in their effects on queen hibernation survival, longevity and fitness. In addition, multiply inseminated queens always had a lower performance as compared to singly inseminated queens. Apart from these main effects, sire groups (in situations of multiple insemination) affected queen longevity and fitness not independently of each other, i.e. certain sire group combinations were more harmful to queens than others. So far, the cause(s) of these effects remain(s) elusive. Harmful male traits as detected here are not necessarily expected to evolve in social insects because males depend on females for a successful completion of a colony cycle and thus have strong convergent interests with their mates.
PMID: 15705558

12: Ageing studies on bats: a review.
Biogerontology. 2004;5(4):211-22. Review.
Brunet-Rossinni AK, Austad SN.
Department of Biological Sciences, University of Idaho, P.O.Box 443051, Moscow, ID 83844-3051, USA.
Bat biologists have long known about the exceptional longevity of bats (Order: Chiroptera), which is unusual for mammals of such a small size and a high metabolic rate. Yet relatively few mechanistic studies have focused on this longevity. On average, species of Chiroptera live three times longer than predicted by their body size. In addition, bats have other life history traits that are characteristic of large, long-lived mammals such as few and large offspring and slow growth rates. Bats fit the evolutionary theory of ageing, as their extended longevity is predicted by their ability to escape extrinsic mortality through flight and, in some species, hibernation. They also show tradeoffs between longevity and reproduction, as predicted by the disposable soma theory of ageing. From a physiological perspective, bat longevity reportedly correlates with replicative longevity, low brain calpain activity, and reduced reactive oxygen species production. As long-lived and physiologically interesting organisms, bats may prove to be an informative model system for ageing research.
PMID: 15314271

13: Life history, ecology and longevity in bats.
Aging Cell. 2002 Dec;1(2):124-31.
Wilkinson GS, South JM.
Department of Biology, University of Maryland, College Park, MD 20742, USA.
The evolutionary theory of aging predicts that life span should decrease in response to the amount of mortality caused by extrinsic sources. Using this prediction, we selected six life history and ecological factors to use in a comparative analysis of longevity among 64 bat species. On average, the maximum recorded life span of a bat is 3.5 times greater than a non-flying placental mammal of similar size. Records of individuals surviving more than 30 years in the wild now exist for five species. Univariate and multivariate analyses of species data, as well as of phylogenetically independent contrasts obtained using a supertree of Chiroptera, reveal that bat life span significantly increases with hibernation, body mass and occasional cave use, but decreases with reproductive rate and is not influenced by diet, colony size or the source of the record. These results are largely consistent with extrinsic mortality risk acting as a determinant of bat longevity. Nevertheless, the strong association between life span and both reproductive rate and hibernation also suggests that bat longevity is strongly influenced by seasonal allocation of non-renewable resources to reproduction. We speculate that hibernation may provide a natural example of caloric restriction, which is known to increase longevity in other mammals.
PMID: 12882342 [PubMed - indexed for MEDLINE]

14: Effects of aging and caloric restriction on the gene expression of Foxo1, 3, and 4 (FKHR, FKHRL1, and AFX) in the rat skeletal muscles.
Microsc Res Tech. 2002 Nov 15;59(4):331-4.
Furuyama T, Yamashita H, Kitayama K, Higami Y, Shimokawa I, Mori N.
Department of Molecular Genetics, National Institute for Longevity Sciences (NILS), Aichi, Japan.
In C. elegans, insulin-like hormone signal pathway plays a significant role in longevity. In particular, daf-16 gene product is indispensable factor for this lifespan-extension. This signal pathway is critical for dauer formation, which is a similar state to hibernation in mammals. We examined the expression level of mammalian daf-16 homologues, Foxo 1,3, and 4 (FKHR, FKHRL1, and AFX) mRNAs in the rat skeletal muscles during aging and in 30% caloric restricted of ad libitum fed. The expression level of AFX mRNA was significantly higher at 6 and 12 months than at 3 and 26 months, and FKHRL1 expression was significantly higher at 6 months than at 3 and 26 months but FKHR expression showed no significant change with age. We observed a characteristic expression of AFX and FKHR mRNAs to be significantly higher in the second day in caloric restriction by every-other-day feeding than in ad libitum fed. This suggests that caloric restriction may increase the expression of FKHR-family genes and prevent the aging process in the skeletal muscles. Copyright 2002 Wiley-Liss, Inc.
PMID: 12424797 [PubMed - indexed for MEDLINE]

15: Effects of size and temperature on metabolic rate.
Science. 2001 Sep 21;293(5538):2248-51. Erratum in: Science 2001 Nov 16;294(5546):1463.
Gillooly JF, Brown JH, West GB, Savage VM, Charnov EL.
Department of Biology, The University of New Mexico, Albuquerque, NM 87131, USA.
We derive a general model, based on principles of biochemical kinetics and allometry, that characterizes the effects of temperature and body mass on metabolic rate. The model fits metabolic rates of microbes, ectotherms, endotherms (including those in hibernation), and plants in temperatures ranging from 0 degrees to 40 degrees C. Mass- and temperature-compensated resting metabolic rates of all organisms are similar: The lowest (for unicellular organisms and plants) is separated from the highest (for endothermic vertebrates) by a factor of about 20. Temperature and body size are primary determinants of biological time and ecological roles.
PMID: 11567137

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See also:

"Animals that save energy by hibernation or lethargy, for instance bats and hedgehogs, live much longer than those who are always active. This is particularly obvious in closely related animals. Thus, white-toothed and red-toothed shrews can be differentiated by the presence or lack, respectively, of a state of lethargy for saving energy. White-toothed shrews (capable of lethargy) become much older (4-6 years) than their almost equally large red-toothed relations (2-3 years), who are not capable of lethargy."

Cited from:
"Programmed ageing: the theory of maximal metabolic scope"
EMBO Rep. 2005 July; 6(S1): S14-S19. doi: 10.1038/sj.embor.7400425.
Roland Prinzinger, Chair and Head of the Department of Metabolic Physiology at the Johann-Wolfgang Goethe University, Frankfurt/Main, Germany.

See also:

"Interestingly, some evidence suggests that hibernation retards aging (Lyman et al., 1981; Wilkinson & South, 2002) and certain aspects of the physiological state of caloric restriction resembles hibernation (Walford & Spindler, 1997)."

Cited at p.456 in:
A Critical Evaluation of Nonmammalian Models for Aging Research
Steven N. Austad and Andrej Podlutsky, pp.449-467.
Handbook of the Biology of Aging, 2006

Lyman et al (1981) Hibernation and longevity in the Turkish hamster Mesocricetus bradti. Science, 212, 668-670

Wilkinson G.S. & South J.M., (2002) Life history, ecology and longevity in bats. Aging Cell, 1, 124-131.

Walford R.L.& Spindler S.R., (1997) The response to caloric restriction in mammals shows features also common to hibernation: a cross-adaptation hypothesis. Journal of Gerontology A: Biological Sciences and Medical Sciences, 52, B179-BB183

Cited from:

Lessons from the differential expression of genes controlling carbon utilization in mammalian hibernators have revealed similarities with hypometabolic states in organisms with well-defined genetics. Similarities among the expression of PDK4 during hibernation, the activation of PDK4 in diabetic (low insulin) rodents (258, 260), and the reduction in glucose-based metabolism due to a defective insulin-like receptor in dormant nematodes (146), suggest a conserved mechanism for the molecular control of carbon utilization in mammalian hibernation and nematode diapause Diapause in the nematode Caenorhabditis elegans is characterized by increased fat accumulation and arrested development resulting in the dauer larva stage. For periods of up to 6 mo dauer larvae do not feed, show no movement, and undergo a reduction in glucose-based catabolism (reviewed in Ref. 206). When environmental conditions become more favorable, as seen with spring emergence in hibernating mammals, dauer larvae will resume development and are nearly indistinguishable from individuals that have not arrested at the dauer stage. Genetic analysis has shown that a protein homologous to the mammalian insulin/insulin-like growth factor (IGF-I) receptor, called DAF-2, is a key player in the switch from a normal life cycle to the arrested dauer stage (146). Dauer larvae formation will occur constitutively when a mutation in the daf-2 gene produces a receptor that is defective in the ligand-binding domain. Hence, the inability of an insulin-like ligand to bind DAF-2 leads to a state of dormancy and metabolic rate depression analogous to hibernation in mammals.
Genetic conservation between insulin signaling in mammals and diapause signaling in C. elegans is also seen early in the dauer signal transduction pathway where mutant age-1 alleles cause a dauer constitutive phenotype. The AGE-1 protein is closely related to a family of phosphatidylinositol 3-kinase p110 catalytic subunits thought to associate with the insulin receptor and provide the next step of the insulin-signaling pathway in mammals (182).

Partial activation of the dauer pathway by various daf-2 and age-1 mutants in C. elegans (reviewed in Refs. 59 and 116) results in an extension of life span similar to that seen in hibernating mammals (166).

A 75% decrease in circulating IGF-I in hibernating golden-mantled ground squirrels (213) suggests a reduction in IGF-I signaling similar to that seen in the long-lived C. elegans mutants. In addition, knock-out mice that are heterozygous null for the IGF-I receptor live 26% longer than their wild-type littermates (130). It is possible that an element of the increased longevity associated with hibernation results from elevated PDK4 activity, which reduces carbohydrate oxidation and thus mimics the life-extending effects of caloric restriction in mammals (251).
Recently, daf-2 mutants have also been shown to confer resistance to hypoxia in C. elegans (215). As with the reversibility of low oxygen consumption during arousal from hibernation in mammals, these hypoxia-resistant mutants (Hyp) fully recover from up to 20 h of extremely low oxygen concentrations (215). Nonetheless, it is interesting that various phenotypes associated with hibernation in mammals are also seen with mutants of a single gene encoding an insulin-like receptor in worms.
The physiological and biochemical changes that occur in mammalian hibernators are similar in some respects to those observed in lower vertebrates and invertebrates that undergo estivation and other forms of dormancy. These include the seasonal deposition of fuel reserves, typically in the form of lipid; the switch from carbohydrate to lipid oxidation during periods of metabolic depression; depression of RNA and protein synthesis and degradation; use of reversible phosphorylation of enzymes and other proteins as means to rapidly control metabolic processes; and evidence of increased oxidative stress and antioxidant defenses in certain tissues (108, 109, 112, 121, 227).


If, as some contend, reduced metabolic rate leads to the (relative) retardation of aging, then the practice of the classic meditative regimen may indeed be associated with significant retardation of aging and/or extension of life span and health span on the basis of much data on the metabolism-lowering effects of meditation. Of particular interest in this regard are studies by researchers from Stanford,19 Harvard,20 Rockefeller University,21 and other research institutions on the special ability of some long-term, virtuoso yoga practitioners to induce and maintain profoundly lowered metabolic rates during meditation, with reductions ranging from 38–64% below resting levels! Such lowered metabolism is actually within the range of hibernating animals,22 and hibernation has been associated with extended longevity in some studies because of lowered metabolism, according to some investigators23 (although not others24).

Reference 24:

J Gerontol. 1991 Mar;46(2):B47-53.Related Articles,Links

Mammalian aging, metabolism, and ecology: evidence from the bats and marsupials.
Austad SN, Fischer KE.
Department of Organismic and Evolutionary Biology, Harvard University.

This study compared trends in body size, life span, metabolic rate, and ecology of bats and marsupials with those from mammals generally, using a 580 species data base. The linear logarithmic relationship between mammalian body mass and maximum longevity, deleting bats and marsupials, is used as a standard against which to measure life spans of particular mammal groups. Bats have maximum life spans a minimum of 3 times those of nonflying eutherians--a trend resulting from neither low basal metabolic rate, the ability to enter torpor, nor large relative brain size. Marsupials live about 80% as long as nonflying eutherians despite averaging lower basal metabolic rates; similarly, there is no effect of heterothermy or relative brain size. These results directly conflict with predictions of both "rate of living" and brain-size mediated theories of aging. However, they are consistent with an evolutionary theory that posits exceptionally long life spans among mammals with reduced environmental vulnerability.

1 comment:

canan said...


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