Evolutionary Biology 19: Aging

Question 1

Difference between a proximate answer to why organisms age and an ultimate answer to why organisms age?

Answer 1

Ultimate (evolutionary) explanations - WHY we age?

Proximate (mechanistic) explanations - HOW we age?

Question 2

Difference between extrinsic and intrinsic mortality?

Answer 2

Extrinsic - death rate outside factors e.g. predation, bad weather, infectious disease

Intrinsic - death rate caused by factors inside the organism - senescence (aging)

Question 3

3 evolutionary genetics theories?

Answer 3

Mutation accumulation theory

• mutations which have a delayed detrimental phenotype (don’t show themselves until later in life) are not selected against in the wild as the organism is usually dead from extrinsic factors
• therefore build up in germline over generations and cause intrinsic death

Antagonistic Pleitropy
- genes with beneficial effects in early life have detrimental effects in later life (when selection is week due to extrinsic mortality)

Disposable Soma theory

• body must budget energy available to it, scarcity in resources means repair is compromised
• over life-time somatic issues, errors in repair etc. accumulate

Question 4

Experiment for artificially increased extrinsic mortality? Results?

Answer 4

Curtailing Lifespan experiment with Musca domestica
- Kept in 2 populations, 1000 adults, 130 adults

Reproduction curtailed after 4-5 days mimicking extrinsic mortality

Results consistent with late acting genes being rendered neutral and increasing in frequency by random drift

• evidence of trade-off between reproductive fitness and longevity

Question 5

Famous example of gene exhibiting antagonistic pleitropy?

Answer 5

P53 gene

• Over activation of P53 leads to protection from tumours but early onset of aging phenotype
• > antagonistic pleitropy

Question 6

Daf-2 effects in C. elegens?

Answer 6

partial mutation of daf-2 significantly increases longevity

• > at cost of reproductive rate
• > mutants are out-competed