Lecture 17 - Aging & Disease
Transcript of Lecture 17 - Aging & Disease
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AGING AND DISEASEPSYCH 118 June 4, 2013
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SENESCENCE
Senescence: an age-specific decline in survival.
Senescence is occurring if the probability of dying - or reproducing fewer or less-healthy offspring per year - increases with increasing age.
Example: Red deer reproductive rates on Rum Island in Scotland
(Nussey et al. 2006)
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DO WILD ANIMALS SENESCE?
Yes.
Example: Comparative senescence
in wild mammals Promislow (1991)
49 species of mammal in 56 populations
Evidence of senescence in 46 populations
There is a tradeoff between the timing of
senescence and intensity of reproductiveeffort
Males may senesce earlier and more rapidlythan females, perhaps due to energeticinvestments in male-male competition
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EVOLUTION OF SENESCENCE
The Antagonistic Pleiotropy Model
The Disposable Soma Model
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ANTAGONISTIC PLEIOTROPY
Pleiotropy: when a gene has more than one effect on an organism.
George Williams (1957)
Natural selection should act more strongly early in life (can havemore impact on reproductive career).
Antagonistic pleiotropy occurs when a gene is selected for early inlife due to some benefit, but also causes a detriment later in life.
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ANTAGONISTIC PLEIOTROPY
Example:Abnormal
abdomen gene in fruit flies
(Drosophila), Templeton et al.1985
Causes juvenile cuticle to remaininto adulthood
Causes early ovarian developmentand oviposition (early good!)
Also decreases longevity andspeeds up senescence (later bad!)
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DISPOSABLE SOMA THEORY
Longevity and senescence can have a complex relationship.
Kirkwood (1977)
Bodies shift resources to reproduction from other systems (which subsequently fall intodisrepair).
Not mutually exclusive from antagonistic pleiotropy
Longevity should be lower in:
Species that make large investments in traits that are related toreproduction
The sex that invests the most in reproduction
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DISPOSABLE SOMA THEORY
Example: Disposable soma
theory in humans, Lycett et al. 2000
16,500 families in Germany from1720-1870, divided into 3 economic strata
Predictions:
Married women should haveshorter lifespans than non-married (nope)
A negative relationship betweenlifespan and fecundity (nope)
Control for duration of marriage...
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DISPOSABLE SOMA THEORY
Example: Disposable soma theory intsetse flies, Clutton-Brock and Langley 1997
Does simply having mated change longevity?
No.
Sex ratio, on the other hand...
When females in the minority, F
lifespan reduced
When males in the minority, M
lifespan reduced
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PROXIMATE MECHANISMS OF
AGING Glucocorticoids, stress, and aging
Sapolsky: the effects of stress and chronic highglucocorticoid levels in animals (and humans) mimic those ofaging
Proximate mechanisms may be similar
Stress and aging in the hippocampus: disrupted hippocampal-dependent learning, inhibited nerve growth, neuron repairfailure, facilitated neuron death
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PROXIMATE MECHANISMS OF
AGING Heat-shock proteins and aging
Heat-shock proteins are activated by heat, and act to minimize stress damage by
neutralizing other heat-warped proteins
There is a strong relationship between senescence and the efficiency of heat-shock protein systems
Tatar et al. 1997: tested resilience to stress in fruit flies inrelation to heat-shock proteins
Added 12 extra copies of heat-shock protein in a strain of flies. When exposedto heat shock at 4 days old, the modified strain had lower mortality rates overtime.
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DISEASE AND ANIMAL
BEHAVIOR Diseases are ubiquitous and rapidly evolving
There are behavioral mediations that animals can do toreduce susceptibility to disease
Avoid areas that contain disease-causing agents
Avoid sick conspecifics
Self-medicate
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AVOIDANCE OF DISEASE-
FILLED HABITATS One way is to only produce offspring in areas
with a low probability of infection (from, e.g.,parasites)
Example: Oviposition andenvironmental parasite levels in graytreefrogs (Hyla versicolor), Kiesecker &Skelly 2000
Frogs share ponds with a snail that is host to a
trematode parasite
Do ovipositing frogs distinguish betweensites based on snail presence as a proxyfor parasite presence?
Do frogs respond to the density of snails?
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AVOIDANCE OF DISEASE-
FILLED HABITATS Kiesecker & Skelly set up 25 artificial ponds with 5
treatments:
no snails (control)
5 infected snails
5 uninfected snails
10 infected snails
10 uninfected snails
66.1% of all eggs laid in the control pond
Ponds with uninfected snails got 33.5%
Ponds with infected snails only got 0.4%!
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AVOIDANCE OF DISEASED
INDIVIDUALS In bullfrogs (Rana catesbeina), the
intestinal pathogen Candidahumicola can spread quickly,hamper reproduction, and kill
Tadpoles in close contact withinfected individuals are likely tobecome infected
Kiesecker et al. 1999: Do
uninfected tadpoles avoidinfected individuals? How
do they know?
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AVOIDANCE OF DISEASED
INDIVIDUALS Researchers put two tadpoles in an arena:
Stimulus: 2 tadpoles placed on eitherside of an arena, 1infected withC.humicola and 1not
Focal: placed in center of arena, thenquantify how much time it spendsnear which tadpole
Uninfected focals preferred uninfected stimuli
Infectedfocals showed no preference
Quarantine behavior was entirely dependentupon disease status!
Disease status was discerned via chemical cues
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SELF-MEDICATION
Two broad categories:
Preventative
Therapeutic
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PREVENTATIVE SELF-
MEDICATION Animals add anti-bacterial substancesto their nests
Swallows that add fresh herbsto their nest have lower miteloads
Eating clay, dirt, and rocks
(geophagy)may be self-medication
No nutritional value, but mayaid in indigestion, anti-diarrhea,and may absorb plant toxins
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FUR RUBBING AND ANTING
Anting: crush ants and rub theminto feathers. Formic acid secreted by
ants soothes skin and kills parasites(also seen in squirrels and primates).
http://www.youtube.com/v/314-HtWIOps
In capuchins it most often occursduring the dry season (when ticksare most prevalent) and it reduces
the number of ticks (Verderane et al.2007)
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http://www.youtube.com/v/314-HtWIOpshttp://www.youtube.com/v/314-HtWIOpshttp://www.youtube.com/v/314-HtWIOpshttp://www.youtube.com/v/314-HtWIOpshttp://www.youtube.com/v/314-HtWIOpshttp://www.youtube.com/v/314-HtWIOps -
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FUR RUBBING AND ANTING
Fur rubbing: insteadof rubbing ants, they
bite acidic fruits, herbs,millipedes, noxious sapsand then rub the salivamixture into their fur.Can be a social
behavior.
Most rubbing itemshave anti-microbialeffects
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LEAF SWALLOWING
Example: Leaf swallowing
and tapeworms in
chimpanzees, Wrangham 1995
During 7-month tapeworm season,chimps swallowed leaves more often(although its unclear if it is aneffective treatment
Neighboring groups have convergedon the same leaves during tapewormseason... individual learning, or cultural
transmission of self-medication?
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SPICY FOOD AS SELF-
MEDICATION
Before freezers, how might humans have fought food-bourne disease?
Billing & Sherman: Examined 43 spices in meat-based cuisines from 4,578 recipes in 30 countries
There was no correlation between spice use and availability, nutritional value, odors, or perspiration
All 43 spices examined DID have some antimicrobial properties
As mean annual temperature increased - along with the potential for meat to spoil rapidly - so did spice use,especially use of the most potently anti-microbial spices!