Life history and longevity
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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.
• 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.
Exponential population growth
b = birth rate
d = death rate
r = intrinsic rate of
population growth
dN/dt = (b-d)N
= rN
“r-selected”
Logistic population growth
Addition of a density dependent term results in logistic growth
K = carrying capacity
dN/dt = rN (K-N)/K
“K-selected”
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
The age-specific survival (lx) and
fertility (mx) pattern specifies an
organism’s life history pattern.
Fertility (mx) patterns
Estimating
Survivorship (lx)
(lx)
Survivorship types
Survivorship
curve examples
Bat survivorship curves
Desmodus
rotundus
females
100
Eptesicus
fuscus
males
10
Eptesicus
fuscus
females
Age (years)
19
17
15
13
11
9
7
5
3
1
1
Lo g survivo rship
1000
r vs K selected
Life history trade-offs
expected with limited resources
Lizards
Due to allocation of resources
between maintenance and
reproduction
Birds
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
Reproductive
value curves
Lizards
Crustacea
Beetle
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
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)
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)
Possible factors influencing
extrinsic mortality risk in bats
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Body size
Group size
Cave roosting
Diet
Hibernation (Latitude)
Reproductive rate
Longevity records for bats
Data sources on longevity
Distribution by family
56 from publications
8 from unpublished studies
Pteropidae - 5
Emballonuridae - 1
Megadermatidae - 1
Rhinolophidae - 4
Noctilionidae - 1
Phyllostomidae - 8
Molossidae - 2
Vespertilionidae - 42
Distribution by source
Captive - 16
Field - 48
ANOVA: F 1, 62 = 1.3, P = 0.25
ANOVA (log long): F 7, 56 = 2.1, P = 0.064
Phylogenetically
independent
contrasts
were used to
infer correlated
evolution
Longevity and body mass in
nonflying eutherian mammals
(Austad & Fischer, 1991)
Species means
Longevity (y)
50
F 1,62 = 1.5, P = 0.23
10
3
10
100
Body mass (g)
1000
Change in longevity (log y)
Longevity and body mass in bats
Independent contrasts
0.3
F 1,40 = 7.3, P = 0.01
0.2
0.1
0
-0.1
-0.2
0
0.1
0.2
0.3
0.4
Change in body mass (log g)
Allometric relationship for 463 spp of nonflying placental mammals (Austad & Fischer 1991)
Roosting and group size variation
Longevity (y)
50
10
F 1,60 = 1.5, P = 0.22
3
1
10
100
1000
Colony size
10000
100000
Change in longevity (log y)
Colony size and longevity
0.3
0.2
0.1
0
-0.1
-0.2
F 1,38 = 0.4, P = 0.52
-0.3
0
0.5
1
Change in log colony size
1.5
40
F 2,61 = 4.6, P = 0.014
(a)
Longevity (y)
46
11
7
10
1
Always
Sometimes
Never
Cave roosting
Change in longevity (log y)
Roosting habits and longevity
0.1
(b)
F 1,11 = 5.9, P = 0.033
0.05
0
Always/never
Sometimes
Change in cave roosting
Bat diets
40
F 1,62 = 0.04, P = 0.84
54
Longevity (y)
10
10
1
Frugivorous
Animalivorous
Diet
Change in longevity (log y)
Frugivory and longevity
0.1
F 1,2 = 0.1, P = 0.81
0.05
10
0
54
-0.05
-0.1
No
Yes
Change in fruit eating
Reproductive effort variation
1 pup/yr
Rhinolophus darlingi
1 pup/4-6 mos
2 pups/yr
Carollia perspicillata
Nyctophilus gouldi
Longevity (y)
50
(a)
10
3
F 1,62 = 23.6, P = < 0.0001
Change in longevity (log y)
Reproductive effort and longevity
0.2
(b)
0.1
0
-0.1
-0.2
F 1,40 = 19.4, P = < 0.0001
-0.3
1
2
Reproductive rate
3
0
0.5
1
Change in reproductive rate
Hibernation
Twente et al. 1985
40
Longevity (y)
F 1,60 = 13.7, P = 0.0005
39
23
10
1
No
Yes
Hibernation
Change in longevity (log y)
Hibernation and longevity
0.15
F 1,5 = 10.3, P = 0.024
0.1
0.05
0
No
Yes
Change in hibernation
Change in longevity (log y)
Latitude and longevity
Longevity (y)
40
30
20
10
F 1,62 = 14.6, P = 0.0003
0
0
10
20
30
40
50
Species mid-range latitude
60
0.3
0.2
0.1
0
-0.1
-0.2
F 1,41 = 8.4, P = 0.006
-0.3
0
5
10
15
Change in latitude
20
Multivariate analysis of longevity
(independent contrasts)
Source (controlled*)
Repro. rate (body mass)
Hibernation (rep. rate)
Body mass (rep. rate)
Cave roosting (rep. rate)
df
1,56
1,56
1,56
2,56
F
P
16.9
14.3
5.4
5.2
0.0002
0.013
0.025
0.043
*indicates the independent variable used to generate residual longevities
for the contrast analyses, r2 = 0.58
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.
Implications
• Caloric restriction is the only method for
experimentally increasing lifespan in mammals
• Calorie restricted (and hibernating!) rodents show
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–
–
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Decreased blood glucose
Decreased glycolytic enzyme activity
Increased gamma globulin levels
Increased antioxidant defenses
• Hibernation could act to conserve resources much
like caloric restriction
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
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
Geographic range
Proposed study sites
S ta te/ P ro vin ce
C it y
Al bert a
M ass a chu set ts
M aryl and
F lo rida
C a lga ry
B o ston
C o ll ege Pa rk
T ampa
F irs t
fro st
15 S e pt
5 O ct
11 Oc t
3 Dec
L ast
fro st
23 M a y
3 May
23 A p ri l
25 F eb
F ro st
free d ays
11 5
15 5
17 1
28 1
M o da l
li tte r si ze
1
2
2
2
mtDNA replication
Bat mtDNA control region