Lecture 20

Question 1

Aging/Senescence

Answer 1

• Progressive decline in somatic function reflected in reductions in fertility as well as survivorship
• Caused by progressive degeneration of soma

Question 2

Manifestations of aging

Answer 2

• General degradation of soma
  
  • Impaired function
  • Increased disease
• Increasing mortality rate

Question 3

Costs of reproduction

Answer 3

• High reproductive rates will accelerate senescence and shorten life span

Question 4

Comparative study for costs of reproduction

Answer 4

• Approach: Quantify reproductive effort and assess relationship between effort and lifespan, controlling for size
• Result: Greater reproductive effort is associated with reduced lifespan. Reproductive cost appear to be greater for big dogs

Question 5

Experimental study on female water striders

Answer 5

• Hypothesis: High reproductive rates accelerate senescence and thereby shorten life span
• Design: Manipulate the reproductive rate of females by changing food abundance
• Results: There are costs to reproduction, increased rate of reproduction comes at cost of reduced longevity

Question 6

Evolutionary explanations of aging

Answer 6

• Some evidence to support the idea that reproduction influences longevity
• Mutation accumulation: mutations with late-life deleterious effects accumulate in genome of a species over evolutionary time
• Antagonistic pleiotropy: mutations with beneficial effects early in life may be favored even if those mutations have negative effects late in life

Question 7

Reproductive value

Answer 7

• Expected contribution of offspring to future generations of individuals of age x

Question 8

Cohort of individuals

Answer 8

• A: Early life acting deleterious mutation
• B: Neutral mutations
• C: Late-life acting deleterious mutation
• Big difference in reproductive success (A vs. B and C)
• Small difference in reproductive success (B vs. C)

Question 9

Mutation accumulation theory

Answer 9

• Few survive to older age and those that do are likely to have already reproduced
• Strength of selection declines with age
• Late acting deleterious mutations are not under strong selection and accumulate in genome over evolutionary time

Question 10

Diseases caused by single genes

Answer 10

• Severe diseases that act early in life are rare: 7%
• Most such diseases act during or after reproduction: 93%

Question 11

Antagonistic Pleiotropy Theory

Answer 11

• Few survive to old age, and those that do are likely to have reproduced
• Strength of selection declines with age
• Genes with beneficial effects early in life will be favored in spite of negative effects late in life

Question 12

Experimental evolution of aging

Answer 12

• Hypothesis: Increasing importance of late-life reproduction should generate selection to maintain soma for longer
• Natural reproduction(N): Eggs from young females used to start next generation. Life past day 14 is irrelevant
• Old age reproduction (O): Eggs from old females are used to start the next generation
• Predictions: O lines will evolve greater longevity, O lines will evolve greater late life fecundity
• Conclusions: Rate of senescence can evolve. Antagonistic pleiotropy appears to play a role