Evolutionary and Mechanistic Theories of Ageing Flashcards
What do evolutionary theories of ageing address?
Why organisms age
What do mechanistic theories of ageing address?
How organisms age
Name the evolutionary theories of ageing
Mutation accumulation
Antagonistic pleiotropy
Name the mechanistic theories of ageing
Damage/maintenance
Hyperfunction
In which animal does the chance of death not increase with age?
Hydra
Why is it thought that ageing has evolved as a side effect of another characteristic?
Ageing decreases chance of survival to reproduction - not selected for
What is Medawar’s selection shadow?
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
Which theory did the idea of a selection shadow develop into?
Mutation accumulation theory
What is mutation accumulation theory?
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
What is the antagonistic pleiotropy theory?
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
What is the intrinsic ageing rate thought to have evolved in response to and what is the evidence for this?
Extrinsic hazard level
Extrinsic hazard level varies inversely with animal lifespan
Which evolutionary theory of ageing is there more evidence in favour of?
Antagonistic pleiotropy
What is damage/maintenance theory?
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
What can ROS damage?
Lipids
Proteins
DNA/RNA
How can possible ageing causes be tested?
Use long-lived organisms - see if phenomena linked to death - unexpected early
Study phenomena extending lifespan - show what limiting naturally
What is the main problem with the oxidative damage theory of ageing?
Inconsistent evidence
What is the evidence for the oxidative damage theory of ageing?
Antioxidant enzyme overexpression in transgenic Drosophila extends lifespan - suggests ROS limit lifespan
What is the evidence against the oxidative damage theory of ageing?
Antioxidant enzyme overexpression in mice - no effect on lifespan
What is the hyperfunction theory of ageing?
Ageing due to continued function of WT genes
Gene expression level optimised to reach reproductive maturity - too high after this point
What is the evidence for hyperfunction theory and what could explain this?
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
Which is the newer mechanistic theory of ageing?
Hyperfunction
