Lecture 20 - Evolution of Life Histories

Question 1

What is life history theory?

Answer 1

Life history theory examines the distribution of major events over an individual’s lifetime, including when to grow, reproduce, and how many offspring to produce.

Question 2

What are the central tenets of life history theory?

Answer 2

Trade-offs exist because resources (energy, time) are limited. Allocating resources to one activity (e.g., reproduction) reduces resources available for others (e.g., growth).

Question 3

What are semelparous and iteroparous reproductive strategies?

Answer 3

Semelparous: Reproduce once and die (e.g., wheat, salmon).
Iteroparous: Reproduce multiple times throughout life (e.g., mammals).

Question 4

What determines when an organism starts reproducing?

Answer 4

Trade-offs between early reproduction (shorter generation time, lower survival) and late reproduction (longer lifespan, higher fitness).

Question 5

What is the relationship between offspring size and number?

Answer 5

There is a trade-off; larger offspring survive better, but producing larger offspring means fewer can be produced.

Question 6

What are the costs of early versus late reproduction?

Answer 6

Early reproduction: Faster generation time, but lower individual survival.

Late reproduction: Higher survival and fitness but requires a longer lifespan.

Question 7

What is senescence?

Answer 7

Senescence is the persistent decline in age-specific fitness due to internal physiological deterioration.

Question 8

What are intrinsic and extrinsic mortality?

Answer 8

Intrinsic mortality: Death due to internal factors like organ failure.

Extrinsic mortality: Death due to external factors like predation or environmental hazards.

Question 9

What is the mutation accumulation theory of ageing?

Answer 9

Proposed by Medawar, it states that harmful mutations accumulate because selection weakens later in life.

Question 10

What is the antagonistic pleiotropy theory of ageing?

Answer 10

Proposed by Williams, it suggests that genes beneficial early in life may have detrimental effects later (e.g., early reproduction vs. long-term health).

Question 11

What is the disposable soma theory of ageing?

Answer 11

Proposed by Kirkwood, it suggests a trade-off between reproduction and maintenance due to a limited energy budget.

Question 12

Are the evolutionary theories of ageing mutually exclusive?

Answer 12

No, all three theories (mutation accumulation, antagonistic pleiotropy, disposable soma) may act simultaneously.

Question 13

What are the key trade-offs in life history strategies?

Answer 13

Growth versus reproduction.

Early-life reproduction versus survival and future reproduction.

Offspring number versus offspring size and survival.

Question 14

What is the cost of reproduction?

Answer 14

energy invested in reproduction reduces energy available for growth and maintenance.

Question 15

What drives early versus late maturation?

Answer 15

High juvenile survival favours delayed reproduction.

High adult mortality favours early reproduction.

Question 16

How do guppies in high-predation environments adapt their reproductive strategy?

Answer 16

They reproduce earlier and produce smaller offspring compared to guppies in low-predation environments.

Question 17

How do salmon reproductive strategies vary by region?

Answer 17

Northern salmon conserve energy for multiple breeding events (iteroparous), while southern salmon invest heavily in a single breeding event (semelparous).

Question 18

What is the trade-off demonstrated in body size and fecundity?

Answer 18

Larger body size generally increases fecundity, but growing larger delays reproduction.

Question 19

What is the optimal offspring size for parents?

Answer 19

The size that balances parent energy investment and offspring survival likelihood, ensuring maximum reproductive success.

Question 20

What is the trade-off in offspring investment?

Answer 20

There is a trade-off between the number of offspring and the survival of each. Larger individual offspring often have higher survival rates, but producing them requires greater parental investment.

Question 20

What are semelparous and iteroparous species?

Answer 20

Semelparous species reproduce only once and invest heavily in a single breeding event.

Iteroparous species reproduce multiple times over their lifetime and spread investment across breeding events.

Question 21

What are the key points of life history trade-offs?

Answer 21

Larger body size correlates with greater fecundity.

A negative relationship exists between time and survival.

There’s a trade-off between individual offspring investment and number.

There is an optimal size and age for reproduction to maximise fitness.

Question 22

What are intrinsic and extrinsic mortality?

Answer 22

Intrinsic mortality arises from internal physiological factors like aging.

Extrinsic mortality is caused by external factors like predation or environmental hazards.

Question 23

What are the evolutionary theories of aging?

Answer 23

Mutation Accumulation Theory: Deleterious mutations that affect individuals later in life accumulate in populations because selection weakens with age.

Antagonistic Pleiotropy Theory: Some genes have beneficial effects early in life but harmful effects later.

Disposable Soma Theory: There’s a trade-off between allocating resources to reproduction and body maintenance, leading to senescence.

Question 24

Are the evolutionary theories mutually exclusive?

Answer 24

No, these theories can act simultaneously to explain aging.

Question 25

What is the “fresh blood hypothesis”?

Answer 25

The idea that older individuals are removed to make space for younger, fitter individuals. However, this is not evolutionarily stable.

Question 26

What determines whether an organism is semelparous or iteroparous?

Answer 26

Trade-offs like juvenile versus adult survival, stability of juvenile habitat, and early versus late reproductive success influence this determination.

Question 27

How do environmental factors influence reproductive strategies?

Answer 27

Factors like temperature, migration costs, and habitat stability can affect whether a species prioritises early or late reproduction and how often it reproduces.