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Life history and longevity

Life history and longevity. Population ecology Life history evolution Reproductive value Longevity and senescence. Discussion Readings. Kirkwood, T.B.L. and Austad, S.N. 2000 Why do we age? Nature 408:233-238.

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Life history and longevity

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  1. Life history and longevity • Population ecology • Life history evolution • Reproductive value • Longevity and senescence

  2. Discussion Readings • Kirkwood, T.B.L. and Austad, S.N. 2000 Why do we age? Nature 408:233-238. • Perez-Campo, R., M. Lopez-Torres, S. Cadenas, C. Rojas and G. Barja 1998 The rate of free radical production as a determinant of the rate of aging: evidence from the comparative approach. Journal of Comparative Physiology B 168:149-158. • Brunet-Rossinni AK 2004. Reduced free-radical production and extreme longevity in the little brown bat (Myotis lucifugus) versus two non-flying mammals. Mechanisms of Aging and Development 125: 11-20.

  3. Exponential population growth b = birth rate d = death rate r = intrinsic rate of population growth dN/dt = (b-d)N = rN “r-selected”

  4. Logistic population growth Addition of a density dependent term results in logistic growth K = carrying capacity dN/dt = rN (K-N)/K “K-selected”

  5. Age-specific population growth • Age-specific survivorship (lx) • Age specific reproduction (mx) • Net reproductive rate: Ro = S lxmx • Stable population: Ro = 1 • Growing population: Ro > 1 • Declining population: Ro < 1

  6. The age-specific survival (lx) and fertility (mx) pattern specifies an organism’s life history pattern.

  7. Fertility (mx) patterns

  8. Estimating Survivorship (lx) (lx)

  9. Survivorship types

  10. Survivorship curve examples

  11. Bat survivorship curves

  12. r vs K selected

  13. Life history trade-offsexpected with limited resources Lizards Birds Due to allocation of resources between maintenance and reproduction

  14. Reproductive value • Age-specific expectation of offspring (how much is a female worth in terms of future offspring?) • Assuming a stable population (R = 1) • Vx = (St=xmt lt)/lx • the number of female offspring produced at this moment by females of age x or older / the number of females which are age x at this moment • Reproductive value peaks near puberty in human populations

  15. Beetle Reproductive value curves Lizards Crustacea

  16. Evolutionary theory of aging • The risk of extrinsic mortality should influence life span because the force of natural selection declines with age • Consequently, mutations with late-acting deleterious effects will not be eliminated (antagonistic pleiotropy) • Senescence should result and shorten life span in proportion to mortality risk • Expect that investing in early reproduction will detract from survival - the “disposable soma” idea

  17. Bat Methuselahs Myotis brandti (38 yrs, 8 g) Myotis lucifugus (34 yrs, 7 g) Myotis blythii (33 yrs, 23 g) Plecotus auritus (30 yrs, 7 g) Pteropus Giganteus (31 yrs, 1 kg) Rhinolophus ferrumequinum (31 yrs, 24 g)

  18. Aging studies and bats • Bats are long-lived because they save energy by going into torpor or hibernate (Bouliere 1958) • But, nonhibernating tropical bat species live as long as temperate species (Herreid 1964) • Furthermore, bats live longer than expected for their body size even after adjusting for metabolic differences (Jurgens and Prothero 1987) • And, marsupials, which have lower metabolic rates than bats, have much shorter life spans (Austad and Fischer 1991) • Flying mammals live longer than nonflying mammals (Holmes and Austad 1994)

  19. Possible factors influencing extrinsic mortality risk in bats • Body size • Group size • Cave roosting • Diet • Hibernation (Latitude) • Reproductive rate

  20. Longevity records for bats Data sources on longevity 56 from publications 8 from unpublished studies Distribution by family Pteropidae - 5 Emballonuridae - 1 Megadermatidae - 1 Rhinolophidae - 4 Noctilionidae - 1 Phyllostomidae - 8 Molossidae - 2 Vespertilionidae - 42 ANOVA (log long): F 7, 56 = 2.1, P = 0.064 Distribution by source Captive - 16 Field - 48 ANOVA: F 1, 62 = 1.3, P = 0.25

  21. Phylogenetically independent contrastswere used to infer correlated evolution

  22. Longevity and body mass in nonflying eutherian mammals (Austad & Fischer, 1991)

  23. Longevity and body mass in bats Species means Independent contrasts F 1,40 = 7.3, P = 0.01 F 1,62 = 1.5, P = 0.23 Longevity (y) Change in longevity (log y) Body mass (g) Change in body mass (log g) Allometric relationship for 463 spp of nonflying placental mammals (Austad & Fischer 1991)

  24. Roosting and group size variation

  25. Colony size and longevity Longevity (y) Change in longevity (log y) F 1,60 = 1.5, P = 0.22 F 1,38 = 0.4, P = 0.52 Colony size Change in log colony size

  26. Roosting habits and longevity F 2,61 = 4.6, P = 0.014 (a) (b) F 1,11 = 5.9, P = 0.033 Longevity (y) Change in longevity (log y) Cave roosting Change in cave roosting

  27. Bat diets

  28. Frugivory and longevity F 1,62 = 0.04, P = 0.84 F 1,2 = 0.1, P = 0.81 Longevity (y) Change in longevity (log y) Diet Change in fruit eating

  29. Reproductive effort variation 1 pup/yr 1 pup/4-6 mos 2 pups/yr Rhinolophus darlingi Carollia perspicillata Nyctophilus gouldi

  30. Reproductive effort and longevity (a) (b) Longevity (y) Change in longevity (log y) F 1,62 = 23.6, P = < 0.0001 F 1,40 = 19.4, P = < 0.0001 Reproductive rate Change in reproductive rate

  31. Hibernation Twente et al. 1985

  32. Hibernation and longevity F 1,60 = 13.7, P = 0.0005 F 1,5 = 10.3, P = 0.024 Longevity (y) Change in longevity (log y) Hibernation Change in hibernation

  33. Latitude and longevity Longevity (y) Change in longevity (log y) F 1,62 = 14.6, P = 0.0003 F 1,41 = 8.4, P = 0.006 Species mid-range latitude Change in latitude

  34. Multivariate analysis of longevity(independent contrasts) Source (controlled*) df F P Repro. rate (body mass) 1,56 16.9 0.0002 Hibernation (rep. rate) 1,56 14.3 0.013 Body mass (rep. rate) 1,56 5.4 0.025 Cave roosting (rep. rate) 2,56 5.2 0.043 *indicates the independent variable used to generate residual longevities for the contrast analyses, r2= 0.58

  35. Conclusions • Bats live 3.5 times as long as other mammals of comparable size. • From an evolutionary perspective, extrinsic mortality risk could account for the effects of body size, cave roosting, reproductive rate and hibernation on longevity • From a physiological perspective, the effects of reproductive rate and hibernation on longevity are consistent with allocation of finite resources to the soma.

  36. Implications • Caloric restriction is the only method for experimentally increasing lifespan in mammals • Calorie restricted (and hibernating!) rodents show • Decreased blood glucose • Decreased glycolytic enzyme activity • Increased gamma globulin levels • Increased antioxidant defenses • Hibernation could act to conserve resources much like caloric restriction

  37. Proposed studies on big brown bats • Big brown bats are the most common NA bat • Big brown bats exhibit variation in litter size and hibernation across the species range

  38. Aims - compare four sites • Estimate field metabolic rate, as a proxy for oxygen consumption, using doubly-labeled water and temperature sensitive radio telemetry • Compare seasonal survival at each site using transponder records • Quantify oxidative damage in collagen using flourescent microscopy • Determine if oxygen exposure influences the accumulation of mtDNA damage

  39. Geographic range

  40. Proposed study sites

  41. mtDNA replication

  42. Bat mtDNA control region

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