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Evolution 3 Chapter 13 Aging
Terms in this set (36)
An organism truly perfected for reproduction would?
mature at birth,
continuously produce high-quality offspring in large numbers,
and live forever.
why is this impossible?
All organisms face fundamental trade-offs in their use of energy
the source of much of the
life history variation seen among living organisms?
Whenever there is a trade-off between different components of
fitness (survival and reproduction), we expect natural selection to
favor individuals that?
allocate energy and time with an optimal
balance between benefits and costs, thereby maximizing lifetime
what happened after the possum became sexually mature?
she stopped growing, thereafter
using her energy for metabolism, repair, and reproduction
what does Early sexual maturity mean in a female opossum?
produce more litters in a lifetime, but she will mature with a lesser
body mass and will produce smaller young and/or smaller litters
Many trade-offs in energy allocation are inescapable
selection acts on life histories to adjust energy allocation in a way
that maximizes the total lifetime production of offspring.
Aging (also known as senescence),
is a late-life decline in an
individual's fertility and probability of survival.
why aging persists if it reduces an individuals fitness?
1. Rate of living theory - posits that populations lack the genetic
variation to respond any further to selection against aging.
2. The evolutionary theory - invokes, in part, a trade-off between
the allocation of energy to reproduction versus repair of
Rate of living theory of aging
Aging is caused by the accumulation of irreparable damage to cells
and tissues caused by errors during DNA replication, transcription,
and translation, and by the accumulation of harmful metabolic byproducts.
Populations lack the genetic variation that would enable
them to evolve more effective repair mechanisms than they already
Two predictions made by rate of living theory of aging?
1. Aging rate should be correlated with metabolic rate.
2. Species should not be able to evolve longer life spans, whether
subjected to natural or artificial selection
Is this theory viable?
1.Data on variation in metabolic rate & aging among mammals
refute this theory. 2. Artificial selection experiments refute this theory.
why has The general idea that organisms age and die as a result of intrinsic
physiological limits on cells and tissues persisted?
because cellular and
genetic mechanisms are known that appear to link the aging/senescence of
cells to the senescence of organisms.
what is one such mechanism?
1. Normal animal cells are capable of a limited number of divisions (and
duplications of their chromosomes), after which they cease dividing and die. 2. A portion of the telomere is lost with each cycle of DNA replication and cell
•Telomere shortening is associated with the senescence of cells.
Do populations harbor genetic variation for longevity?
yes, yet longer life spans have not evolved.
evolutionary theory of aging
the failure to completely repair damage is ultimately
caused by either (1) deleterious mutations, or (2) trade-offs between
repair and reproduction as a consequence of natural selection.
Natural selection varies as a function of an individual's age.
one evolutionary explanation for
The accumulation in populations of deleterious mutations whose
effects occur only late in life. Mutations that cause death after reproduction has begun are
selected against less strongly.
Mutations that are selected against only weakly can persist in
In populations of individuals
allowed to live only a short time,
late-acting mutations are?
effectively neutral... Some of these alleles will rise to
high frequency by drift, causing a
decline in natural longevity.
Because natural selection is weaker late in life, alleles that enhance early-life
reproduction may be favored even if they also hasten death.
mutations are pleiotropic if they?
affect two different life history characters
another evolutionary explanation for aging?
Selection for alleles with pleiotropic effects that are advantageous early in life and
deleterious late in life
What kind of mutation could increase reproduction early in life and at
the same time reduce reproduction or survival late in life?
A mutation that causes less energy to be allocated to repair early in life
and more energy to be allocated to reproduction.
Genes that appear to act in this way have been found in a diversity of
organisms from plants to worms, and vertebrates.
The methuselah gene controls?
a trade-off between reproductive success
versus longevity and stress resistance
Do Annuals, which reproduce once and die, allocate more or less energy to their sole bout
of reproduction than perennials?
enhanced reproduction in their first reproductive season at the expense of
drastically accelerated senescence
In populations where ecological mortality rates are high, individuals tend to
earlier in life
Female opossums on Sapelo
Island age more slowly than
female opossums on the
How Many Offspring Should an Individual
Produce in a Given Year?
The more offspring a parent (or pair of parents) attempts to raise at
once, the less time and energy the parent can devote to caring for
Selection will favor the clutch size that produces
the most surviving offspring
Efforts to identify which of Lack's assumptions are violated have led to the
discovery of additional trade-offs and improved estimates of lifetime fitness:
clutch size is not fixed for any given genotype. It is phenotypically
plastic. If clutch size is plastic and birds can predict whether they are going to
have a good year or a bad year, then we would predict that individuals will adjust
their clutch size to the optimum value for each kind of year
Trade-offs across taxa in size and
number of offspring?
There is a negative correlation between size
and number of eggs
What is the optimal compromise between size and number?
Assumptions: 1. Trade-off between size and number.
2. Individual offspring will have a better chance of surviving if they are larger.
why is there is a potential conflict of interest between parents and offspring?
Selection on parents favors a compromise between the quality and
quantity of offspring, but selection on individual offspring favors high
what is driving the
evolution of suboptimal egg
size in heavily
supplemented wild salmon
Gene flow from the hatchery
Life history traits are closely correlated with?
fitness and have relatively
life history traits are intimately connected to reproduction
and selection favors genotypes with the highest fitness. Over time,selection leads to the fixation of the most favorable alleles.
traits therefore show?
less genetic variation - lower heritabilities - than
other kinds of traits.
This set is often in folders with...
CHAPTER 11 - Sexual Selection
Evolution Chapter 10 - Studying Adaptation
Chapter 9: Quantitative Genetics
Evolution Chapter 14 - Evolution and Human Health
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