R20 Evolution of life histories

Question 1

What is the ideal strategy for breeding ?

Answer 1

breed as soon as they are conceived and carry on breeding throughout their life

Question 2

… are the central tenet of life history theory

Answer 2

Trade-offs

Question 3

What is meant by a trade-off?

Answer 3

• Why we can’t have a larger organism reproducing like a rabbit.
• All activities require a resource which is not unlimited
• Resources allocated to one trait (growth) cannot be allocated to another (reproduction)
• Organisms must trade-off one activity with another

Question 4

What is semelparous ?

Answer 4

produce young only once and die, can be seasonal like wheat and butterflies
- invest heavily in their one breeding event

Question 5

What is iteroparous ?

Answer 5

produce young multiple times, can be seasonal (repeated yearly) or random
- investment across the breeding events

Question 6

What is the trade-off in determining whether organisms are semelparous or iteroparous?

Answer 6

• Juvenile survival versus adult survival
• Consistency versus instability of the juvenile habitat (more offspring needed to increase chance of offspring survival in an unstable habitat)
• Energy requirements versus energy availability
• Reliability of adult survival, if survival is variable more likely to be semelparous
• Non-linear costs of reproduction, less upfront costs to reproduction = iteroparous, larger upfront costs = semelparous

Question 7

What are the 5 rules of reproduction (trade-offs)

Answer 7

1) Larger body size generally greater fecundity (ability to produce an abundance of offspring)

2) Negative relationship between time (life time) and number of survivors
- some cases, the young die more frequent so the ones that age go on to age a while
- other cases, lots of individuals live to adult and only some making it to being old

3) There is a trade-off between individual offspring investment and offspring number

4) There is a trade-off between individual offspring investment and offspring survival

5) There is an optimal individual offspring investment for parents, optimal size and age to reproduce (exceeding the optimum would be using energy on making offspring that aren’t going to survive)

Question 8

What is some advantages and disadvantages to early maturation?

Answer 8

• shorter generation time (offspring will reproduce earlier too
• high probability of surviving to maturity
• smaller size for maturity stage (less time to grow)
• low fecundity
• associated with a shorter life span (few breeding attempts)

Question 9

What is some advantages and disadvantages to late maturation?

Answer 9

• larger size of maturity
• higher initial fecundity
• associated with longer life span (more breeding attempts)

Question 10

What is senescence ?

Answer 10

There is a persistent decline in age-specific fitness components due to internal physiological deterioration

Question 11

What is intrinsic mortality ?

Answer 11

mortality due to neglect of maintenance

Question 12

What is extrinsic mortality ?

Answer 12

mortality due to stochastic or environmental factors (e.g., weather or predation)
- natural selection selects against any selection that reduces the number of individuals from reaching maturity. Then there is weak selection for survival past maturity.

Question 13

What is progeny ?

Answer 13

offspring

Question 14

What is the mutation accumulation theory ?

Answer 14

because of weakened selection later in life, deleterious mutations that affect older individuals accumulate in the population
- selected for: if they impact older individuals, selected against: if they impact younger individuals
- these are only for mutations in the germ line not in the soma (somatic)

Question 15

What is antagonistic pleiotropy ?

Answer 15

deleterious mutations that affect older individuals accumulate in populations as they have a positive effect on the younger population and negative effect on older individuals
- Prostate cancer and osteoporosis caused by exposure to testosterone and estrogen support this theory

Question 16

What does pleiotropy mean ?

Answer 16

when a gene affects multiple traits

Question 17

What is the disposable soma theory ?

Answer 17

senescence due to trade-off between allocation to reproduction and maintenance of the soma

Question 18

Is iteroparity or semelparity more common in a unpredictable environment ?

Answer 18

iteroparous, less energy provided by the habitat so can only invest in fewer offspring over a longer period of time

Question 19

Is iteroparity or semelparity more common in a predictable environment ?

Answer 19

semelparous, more energy consuming in a predictable environment

Question 20

What is the problem for warmer climates and mating?

Answer 20

warmer = higher metabolic rate = use more energy = less spare energy for reproduction, more likely to be semelparous
- Example of environmental plasticity

Question 21

What is the advantage to reproducing later in life?

Answer 21

can produce larger offspring

Question 22

What does age-specific mortality and age of reproduction contribute to ?

Answer 22

Age-specific mortality contributes to early versus late maturation, where the benefits of later age of first reproduction are the costs of earlier age of first reproduction, for example, early maturation leads to shorter generation times but smaller offspring

Question 23

What is the rate-of-living hypothesis ?

Answer 23

organisms have a fixed budget by irreparable damage from living, metabolic rate is to do with body mass which in his theory, higher metabolic rate = life span
- Life spans negatively correlated with metabolic rate
- Longevity should not respond to selection (no genetic variation)

Question 24

What is the fresh blood hypothesis ?

Answer 24

old individuals die to make room for young

however, post-reproductive mothers can increase fitness by assisting their own offspring

Question 25

What is an explanation for aging and senescence ?

Answer 25

The weakening of selection post maturation leads to either the
passive accumulation of deleterious mutations impacting later life,
the trade-off between genes that positively impact early life
reproduction and harm later life, and/or a trade-off in the decision
to invest in somatic repair compared to reproduction or germ line
maintenance – which provide an evolutionary explanation for aging
and senescence