Evolutionary and Mechanistic Theories of Ageing

Question 1

What do evolutionary theories of ageing address?

Answer 1

Why organisms age

Question 2

What do mechanistic theories of ageing address?

Answer 2

How organisms age

Question 3

Name the evolutionary theories of ageing

Answer 3

Mutation accumulation

Antagonistic pleiotropy

Question 4

Name the mechanistic theories of ageing

Answer 4

Damage/maintenance

Hyperfunction

Question 5

In which animal does the chance of death not increase with age?

Answer 5

Hydra

Question 6

Why is it thought that ageing has evolved as a side effect of another characteristic?

Answer 6

Ageing decreases chance of survival to reproduction - not selected for

Question 7

What is Medawar’s selection shadow?

Answer 7

More young than old in population - as most die from extrinsic hazard shortly after reproductive age - unlikely to live to old age
Strength of natural selection declines with age - as mutations beneficial/deleterious only in later life not selected for/against - most die before experiencing

Question 8

Which theory did the idea of a selection shadow develop into?

Answer 8

Mutation accumulation theory

Question 9

What is mutation accumulation theory?

Answer 9

In population accumulation of mutations that have deleterious effect only in later life - due to decreased natural selection strength
Decreased natural selection strength due to lack of deleterious mutation effect before reproductive age - passed on to offspring

Question 10

What is the antagonistic pleiotropy theory?

Answer 10

Selection for mutations that beneficial in youth - at price of increased ageing rate
More individuals survive for early benefit than survive to suffer increased ageing rate
Ageing evolves as side effect of natural selection in favour of mutations beneficial in youth

Question 11

What is the intrinsic ageing rate thought to have evolved in response to and what is the evidence for this?

Answer 11

Extrinsic hazard level

Extrinsic hazard level varies inversely with animal lifespan

Question 12

Which evolutionary theory of ageing is there more evidence in favour of?

Answer 12

Antagonistic pleiotropy

Question 13

What is damage/maintenance theory?

Answer 13

Oxidative damage causes ageing - maintenance/repair causes longevity
Competition for resources between maintenance/repair and growth/reproduction
Ageing result of limited investment in maintenance/repair

Question 14

What can ROS damage?

Answer 14

Lipids
Proteins
DNA/RNA

Question 15

How can possible ageing causes be tested?

Answer 15

Use long-lived organisms - see if phenomena linked to death - unexpected early
Study phenomena extending lifespan - show what limiting naturally

Question 16

What is the main problem with the oxidative damage theory of ageing?

Answer 16

Inconsistent evidence

Question 17

What is the evidence for the oxidative damage theory of ageing?

Answer 17

Antioxidant enzyme overexpression in transgenic Drosophila extends lifespan - suggests ROS limit lifespan

Question 18

What is the evidence against the oxidative damage theory of ageing?

Answer 18

Antioxidant enzyme overexpression in mice - no effect on lifespan

Question 19

What is the hyperfunction theory of ageing?

Answer 19

Ageing due to continued function of WT genes

Gene expression level optimised to reach reproductive maturity - too high after this point

Question 20

What is the evidence for hyperfunction theory and what could explain this?

Answer 20

Protein synthesis gene inhibition increases C. elegans lifespan
Could be protein synthesis required for growth - but expression level too high for older organism
Could be due to increased damage clearance

Question 21

Which is the newer mechanistic theory of ageing?

Answer 21

Hyperfunction