Senescence

Question 1

Vx

Answer 1

reproductive value
relative number of female offspring that remain to be born to each female of age x, and how it contributes to the number of individuals in the next generation

Question 2

How does Vx change for a female at the start of her reproductive life vs near the end

Answer 2

high Vx at the start than near the end of her reproductive life

Question 3

How to calculate Vx

Answer 3

sum of mxlx at stage and above, divided by lx stage

Question 4

if the population is increasing, offspring born in the ____ are more valuable than in the equation
if the population decreasing, offspring born in the ____ are relatively less valuable than the equation

Answer 4

near future
near future

Question 5

when are forces of natural selection greatest in terms of the reproductive value

Answer 5

when it operates on age classes with high reproductive values
this is because selection has a large effect on the growth rate and therefore fitness

Question 6

Why would modifier genes that delay expression of deleterious genes have an advantage

Answer 6

have advantage over genes who advance their expression. delaying modifier genes might accumulate in the population leading to increasing mortality after the age of peak Vx

Question 7

Explain Senescence at the individual level

Answer 7

physiological breakdown of the body with increasing chronological change
reduced performance

Question 8

Explain senescence at population level

Answer 8

increased mortality rate and decreased fecundity with chronological age

Question 9

What is the paradox of senescence

Answer 9

senescence decreases individual fitness (individuals that delay senescence should be favoured over those that don’t)… yet senescence is nearly universal

Question 10

What are the two non-evolutionary theories of senescence

Answer 10

1. telomere shortening
2. reactive oxygen species

Question 11

What are the 3 evolutionary theories of senescence

Answer 11

1. mutation accumulation
2. antagonistic pleiotropy
3. disposable soma

Question 12

what is the group selection argument for the theory of senescence

Answer 12

organisms die to make room for future generations

Question 13

Explain the mutation accumulation theory

Answer 13

the mode of action is the mutation shadow on old age classes, that fewer individuals live to be old, therefore selection ignores the older age classes.
assumes = individuals die due to EXTRINSIC reasons and genes can have age-specific effects
ex. huntington’s disease

Question 14

Explain antagonistic pleiotropy theory

Answer 14

the mode of action is that alleles that have beneficial effects early in life and detrimental effects late in life will be selected for. cause to live for shorter periods but reproduce higher in that short period
assumes = genes can have pleiotropic age-specific effects
ex. enhanced calcium deposition (increase bone growth young, lead to hardening of arteries later)

Question 15

Explain Disposable soma theory

Answer 15

the mode of action is organisms allocate resources optimally for maintenance and reproduction. Since life is risky, selection will not favour those that allocate resources to live much longer than their expected lifespan
assume = high cost of body maintenance and tradeoff between maintenance and reproduction

Question 16

What is the problem with mutation accumulation and antagonistic pleiotropy theories

Answer 16

possibility of “time-bomb” in genes, could be combination of senescence and genetic disease

Question 17

What is the problem with the disposable soma theory

Answer 17

the efficacy of repair is about more than just resources - repair mechanisms must evolve and repair mechanisms can also be damaged

Question 18

What is the mortality compensation problem

Answer 18

the maximum mortality rate tends to be shown to be the same even if their trajectory is very different, they increase at different rates but yet all tend to converge at a similar maximum mortality rate