EVOLUTION OF LIFE HISTORIES

Question 1

What does Life History Theory examine?

Answer 1

It examines the distribution of major life events over an individual’s lifetime, focusing on strategies related to growth, reproduction, and survival.

Question 2

What are the main questions Life History Theory addresses?

Answer 2

: Questions include: How big to get? When to start reproducing? How often to breed, and how many offspring to have?

Question 3

What is considered the “ideal” reproductive strategy and why isn’t it common?

Answer 3

The ideal is to reproduce immediately, but this is uncommon because reproduction is energy-intensive.

Question 4

What are the two main reproductive strategies in life history?

Answer 4

Semelparous: Reproduce once and die (e.g., butterflies, mice).

Iteroparous: Reproduce multiple times, either seasonally or randomly.

Question 5

What characterizes semelparous organisms?

Answer 5

They invest heavily in a single breeding event before dying.

Question 6

What characterizes iteroparous organisms?

Answer 6

They spread investment across multiple breeding events over time.

Question 7

How does body size relate to fecundity?

Answer 7

Larger body size generally increases fecundity or fertility.

Question 8

What is the relationship between time and survival in life history?

Answer 8

There is a negative relationship; survival tends to decrease over time.

Question 9

What is the trade-off between offspring investment and offspring number?

Answer 9

Investing more in each individual offspring typically means producing fewer offspring overall.

Question 10

What is the trade-off between individual offspring investment and offspring survival?

Answer 10

: Investing more in each offspring often improves their survival chances but limits the number of offspring that can be produced.

Question 11

What are the optimal conditions for reproduction?

Answer 11

There is an optimal size and age at which organisms should reproduce to maximize fitness.

Question 12

What is senescence?

Answer 12

It is the persistent decline in age-specific fitness components due to internal physiological deterioration, leading to decreased fertility and survival over time.

Question 13

What is intrinsic mortality?

Answer 13

Mortality due to internal causes, such as the body’s neglect of maintenance.

Question 14

What is extrinsic mortality

Answer 14

Mortality caused by external or environmental factors, like accidents.

Question 15

How does the force of natural selection change over an organism’s life?

Answer 15

Early Life:
Natural selection is strongest on traits that affect survival and reproduction. Traits that increase the likelihood of surviving infancy or reaching reproductive age are strongly favored.

Reproductive Age:
During the organism’s reproductive years, selection favors traits that increase reproductive success, such as attracting mates or maximizing offspring survival.

Post-Reproductive Age:
After an organism has reproduced, natural selection becomes weaker. Traits affecting survival or fitness in older age have less impact on evolutionary success because the individual is less likely to pass on its genes at this stage. This is often linked to senescence and the decline in selection pressures after reproduction.It is strongest from birth to maturity and declines exponentially with age.

Question 16

What does the Mutation Accumulation Theory propose?

Answer 16

It suggests that because selection weakens with age, harmful mutations affecting older individuals accumulate in populations.

Question 17

What are the three types of mutations in the Mutation Accumulation Theory?

Answer 17

Type 1: Affects young, not old.

Type 2: Affects old, not young.

Type 3: Affects both young and old.

Question 18

Which mutation types face strong selection against them, and why?

Answer 18

Types 1 and 3 face strong selection because they negatively impact young individuals, who are more critical for fitness.

Question 19

What is antagonistic pleiotropy?

Answer 19

It refers to genes that have beneficial effects on young individuals but detrimental effects on older individuals, leading to a trade-off that favors accumulation of these genes.

examples
- p53 Tumor Suppressor Gene:
Benefit: Early in life, p53 helps prevent cancer by promoting cell death in damaged cells.
Harm: In older age, excessive activation of p53 can contribute to age-related tissue degeneration.
Testosterone:
Benefit: In young males, high testosterone levels promote reproductive success and muscle growth.
Harm: In older males, elevated testosterone levels can increase the risk of prostate cancer and other age-related health issues.

Question 20

What is pleiotropy?

Answer 20

When a single gene affects multiple traits, which can lead to complex trade-offs in life history strategies.

Question 21

What is the Disposable Soma Theory?

Answer 21

It suggests senescence occurs because organisms prioritize energy for reproduction over body (soma) repair, leading to gradual aging and decline.

Question 22

What is the central tenet of life history theory?

Answer 22

Trade-offs are the central tenet, as all activities require resources, which are finite. Resources allocated to one trait (e.g., growth) cannot be used for another (e.g., reproduction).

Question 23

How does resource allocation work in life history theory?

Answer 23

Resources (like time and energy) are finite, so allocating resources to one function means less for others, creating trade-offs.

Question 24

What trade-offs influence whether an organism is semelparous or iteroparous?

Answer 24

Factors like juvenile vs. adult survival, habitat stability, costs of reproduction, and adult survival reliability determine reproductive strategy.

Question 25

How does environment influence the choice between semelparity and iteroparity?

Answer 25

In unstable environments, iteroparity is favored due to multiple breeding chances. In stable environments, semelparity may be favored, allowing a single, massive reproductive event.

Question 26

How does energy allocation affect reproductive strategy?

Answer 26

In unpredictable environments, organisms may use more energy for survival, favoring iteroparity. In predictable environments, organisms can invest in a single massive reproduction event, favoring semelparity.

Question 27

Q: What are some costs associated with early reproduction?

Answer 27

Early reproduction often results in shorter generation times but smaller offspring and lower overall survival.

Question 28

What factors drive early vs. late maturation?

Answer 28

Key factors include genetics, environmental exposures, social and population density, and predation pressure.

Question 29

How does age-specific mortality affect the timing of reproduction?

Answer 29

High age-specific mortality favors earlier reproduction, while low mortality supports later reproduction.

Question 30

What is intrinsic mortality?

Answer 30

Intrinsic mortality is due to internal factors like neglect of maintenance, causing physiological deterioration over time.

Question 31

What is extrinsic mortality?

Answer 31

Extrinsic mortality arises from external or environmental factors, like predation or accidents.

Question 32

How does the weakening of natural selection post-maturation contribute to aging?

Answer 32

As selection weakens with age, deleterious mutations accumulate, and organisms face trade-offs in investing energy in reproduction vs. body repair, leading to aging

Question 33

What does the Rate of Living Hypothesis propose?

Answer 33

It suggests organisms have a fixed energy budget; those with a higher metabolic rate use up their energy faster, leading to shorter lifespans.

Question 34

What are two key predictions of the Rate of Living Hypothesis?

Answer 34

1) Lifespan is inversely related to metabolic rate.

2) Longevity should not respond to selection, as there is no genetic variation in energy budget.

Question 35

What is the Fresh Blood Hypothesis?

Answer 35

It proposes that older individuals die or are removed to make room for younger ones, providing an evolutionary basis for aging.

Question 36

factors that influence age of first reproduction

Answer 36

predation pressure
social and population density
environmental pressures and exposures

Question 37

cost of delaying reproduction

Answer 37

an organism takes on the risk that it may not survive long enough to reproduce, true in environments where mortality rates are high or unpredictable

an organism might miss the chance to reproduce multiple times over its lifetime.

Question 38

potential benefit of delaying reproduction

Answer 38

Delaying reproduction allows an organism to invest more energy in growth and development, which can result in larger, more well-developed offspring. These offspring are often better equipped to survive and compete in their environment. Larger offspring may have higher survival rates, better physical abilities, or enhanced resilience to environmental stresses.

Question 39

environmental factors that influence iteropartity

Answer 39

Stable and Predictable Resource Availability - This allows them to reproduce multiple times, as they can rely on consistent resource availability to support the growth and survival of offspring across breeding seasons.

Low Adult Mortality Rates:adult mortality rates are low and individuals can survive for multiple reproductive cycles, it favors iteroparity.

Moderate or Predictable Environmental Conditions:

low or moderate Predation Pressure:

Question 40

environmental factors that influence semelparity

Answer 40

Unstable and Unpredictable Environments - organisms that reproduce all at once maximize their chances of offspring survival before adverse conditions reduce their ability to reproduce later

High Adult Mortality:

Short Lifespan:

Low Juvenile Mortality: -

Extreme Competition: