Lecture 20 - Evolution of Life Histories Flashcards
What is life history theory?
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.
What are the central tenets of life history theory?
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).
What are semelparous and iteroparous reproductive strategies?
Semelparous: Reproduce once and die (e.g., wheat, salmon).
Iteroparous: Reproduce multiple times throughout life (e.g., mammals).
What determines when an organism starts reproducing?
Trade-offs between early reproduction (shorter generation time, lower survival) and late reproduction (longer lifespan, higher fitness).
What is the relationship between offspring size and number?
There is a trade-off; larger offspring survive better, but producing larger offspring means fewer can be produced.
What are the costs of early versus late reproduction?
Early reproduction: Faster generation time, but lower individual survival.
Late reproduction: Higher survival and fitness but requires a longer lifespan.
What is senescence?
Senescence is the persistent decline in age-specific fitness due to internal physiological deterioration.
What are intrinsic and extrinsic mortality?
Intrinsic mortality: Death due to internal factors like organ failure.
Extrinsic mortality: Death due to external factors like predation or environmental hazards.
What is the mutation accumulation theory of ageing?
Proposed by Medawar, it states that harmful mutations accumulate because selection weakens later in life.
What is the antagonistic pleiotropy theory of ageing?
Proposed by Williams, it suggests that genes beneficial early in life may have detrimental effects later (e.g., early reproduction vs. long-term health).
What is the disposable soma theory of ageing?
Proposed by Kirkwood, it suggests a trade-off between reproduction and maintenance due to a limited energy budget.
Are the evolutionary theories of ageing mutually exclusive?
No, all three theories (mutation accumulation, antagonistic pleiotropy, disposable soma) may act simultaneously.
What are the key trade-offs in life history strategies?
Growth versus reproduction.
Early-life reproduction versus survival and future reproduction.
Offspring number versus offspring size and survival.
What is the cost of reproduction?
energy invested in reproduction reduces energy available for growth and maintenance.
What drives early versus late maturation?
High juvenile survival favours delayed reproduction.
High adult mortality favours early reproduction.
How do guppies in high-predation environments adapt their reproductive strategy?
They reproduce earlier and produce smaller offspring compared to guppies in low-predation environments.
How do salmon reproductive strategies vary by region?
Northern salmon conserve energy for multiple breeding events (iteroparous), while southern salmon invest heavily in a single breeding event (semelparous).
What is the trade-off demonstrated in body size and fecundity?
Larger body size generally increases fecundity, but growing larger delays reproduction.
What is the optimal offspring size for parents?
The size that balances parent energy investment and offspring survival likelihood, ensuring maximum reproductive success.
What is the trade-off in offspring investment?
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.
What are semelparous and iteroparous species?
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.
What are the key points of life history trade-offs?
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.
What are intrinsic and extrinsic mortality?
Intrinsic mortality arises from internal physiological factors like aging.
Extrinsic mortality is caused by external factors like predation or environmental hazards.
What are the evolutionary theories of aging?
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.
Are the evolutionary theories mutually exclusive?
No, these theories can act simultaneously to explain aging.
What is the “fresh blood hypothesis”?
The idea that older individuals are removed to make space for younger, fitter individuals. However, this is not evolutionarily stable.
What determines whether an organism is semelparous or iteroparous?
Trade-offs like juvenile versus adult survival, stability of juvenile habitat, and early versus late reproductive success influence this determination.
How do environmental factors influence reproductive strategies?
Factors like temperature, migration costs, and habitat stability can affect whether a species prioritises early or late reproduction and how often it reproduces.
