Lecture 17 - Aging & Disease

7/28/2019 Lecture 17 - Aging & Disease

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AGING AND DISEASEPSYCH 118 June 4, 2013

Tuesday, June 4, 13


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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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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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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)

Tuesday, June 4, 13
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!

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Lecture 17 - Aging & Disease