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ISCI 350 > Senescence > Flashcards

Senescence Flashcards

1
Q

senescence

A
  • late-life decline in fertility/survival
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2
Q

‘rate of living’ theory of aging (4)

  • type of theory
  • reason for senescence
  • evolution of organism lifespan
  • do we need to explain senescence?
A
  • non-evolutionary theory of aging
  • damage results from accumulation of poisonous metabolites and errors in DNA replication
  • organisms have evolved longest life spans that are physiologically possible
  • no, wear-and-tear hypothesis says that senescence results from inevitable accumulation of damage to cells and tissues
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3
Q

predictions of ‘rate of living’ theory (2)

A
  • aging rate should be correlated with metabolic rate:
    • slower metabolic rate -> long life span
    • faster metabolic rate -> short life span
  • selection for longer life spans should not be possible
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4
Q

why is the ‘rate of living’ theory incorrect (2)

A
  • selection for longer life spans should not be possible, but it is
  • wear and tear alone is not sufficient to explain senescence
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5
Q

assumptions of the ‘rate-of-living’ theory that are testable (2)

A
  • comparative tests among mammals: total lifetime energy expenditure should be the same across organisms, but it is not
  • experimental tests among flies: artificial selection should not increase life span, but it does
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6
Q

do we need to explain senescence? (2)

A
  • yes: senescence is affected by factors under genetic control (and subject to natural selection) that may slow aging
  • ‘rate of living’ theory of aging has been refuted because wear and team alone is not sufficient to explain senescence
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7
Q

reasoning behind evolutionary theories of senescence: older age class representation in populations

A
  • older age classes less represented in populations due to constant risk of death from accidents, predators, etc
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8
Q

reasoning behind evolutionary theories of senescence: how does selection act on deleterious alleles of late expression vs early expression (2)

A
  • selection on deleterious alleles of late expression should be WEAK, but selection on deleterious alleles of early expression should be STRONG
  • change in fecundity or survival from one age interval to the next has great effect on overall fitness if it occurs early than late in life
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9
Q

according to the evolutionary theories of aging, what is the senescence the consequence of?

A
  • senescence is an inevitable consequence of the fact that the strength of natural selection declines with age
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10
Q

mutation accumulation hypothesis (2)

  • type of evolutionary theory
  • hypothesis
A
  • evolutionary theory of aging
  • germ-line deleterious mutations expressed late in life accumulate in populations due to lack of strong selection to weed them out
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11
Q

antagonistic pleiotropy hypothesis (2)

  • type of evolutionary theory
  • hypothesis
A
  • evolutionary theory of aging

- germ-line deleterious mutations expressed late in life are selected for if they increase fitness early in life

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12
Q

mutation accumulation hypothesis assumption

A
  • relative fitness of alleles will likely decrease in late life as these alleles are not selected as strongly for
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13
Q

mutation accumulation hypothesis prediction

A
  • effect of inbreeding depression is expected to increase with age
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14
Q

antagonistic pleiotropy hypothesis assumptions (3)

A
  • selected for: alleles with high relative fitness in early age will have low relative fitness in late age
  • not selected for: alleles with low relative fitness in early age will have high relative fitness in late age
  • essentially, there is a trade-off between longevity and fecundity
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15
Q

antagonistic pleiotropy hypothesis prediction (3)

A
  • effect of inbreeding depression NOT expected to increase with age
  • selection for later reproduction or REDUCES fecundity should INCREASE life span
  • selection for LONGER life span REDUCES fecundity
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16
Q

genes with pleiotropic effects (3)

A
  • immune systems chemicals
  • gene for iron absorption
  • p53 tumour suppressor protein
17
Q

how do immune system chemical have pleiotropic effects (2)

A
  • chemicals protect from infection

- chemicals also damage host tissues

18
Q

how does the gene for iron absorption have pleiotropic effects

A
  • protects from iron deficiency anemia (especially in menstruating women)
  • may contribute to death in middle age due to excess iron absorption (hemochromatosis)
19
Q

how does p53, a tumour suppressor gene have pleiotropic effects

A
  • signals cells to stop dividing when damaged

- may cause stem cells to stop dividing prematurely

20
Q

telomeres (3)

  • benefit
  • concern
  • prevention
A
  • protect ends of chromosomes
  • progressively shorten during division of somatic cells
  • to reduce rate of telomere shortening: do not smoke, eat well, sleep enough, exercise regularly and cut down on stress
21
Q

the problem of menopause (2)

A
  • why does gamete production terminate abruptly in women, yet tapers off in men
  • why does menopause occur so early in like, when other vital functions are still strong
22
Q

humans compared to other primates (3)

  • age at weaning
  • development
  • lifespan
A
  • reduced age of weaning
  • extended development
  • lengthened lifespan
23
Q

non-adaptive hypotheses of menopause (2)

A
  • phylogenetic inertia

- artifact of modern lifestyle

24
Q

adaptive hypotheses of menopause (3)

A
  • mother hypothesis
  • ‘grandmother’ hypothesis
  • reproductive competition between generations
25
Q

mother hypothesis (2)

A
  • menopause evolved to avoid higher reproductive-mediated mortality risk in late-life
  • ensure the survival of existing offspring born in very immature state
26
Q

‘grandmother’ hypothesis (2)

A
  • grandmothers can help daughters have more offspring
  • post-reproductive mothers enhance the lifetime reproductive success of their offspring by allowing them to breed earlier, more frequently, and more successfully
27
Q

what is a proposed explanation for how menopause may have evolved

A
  • a combined model incorporating the mother and grandmother hypotheses
28
Q

what are the varying effects of factors of the mother hypothesis alone at different ages of menopause (2)

A
  • varying probability of mother’s death in childbirth

- varying effect of mother’s death on juvenile survival

29
Q

what are the varying effects of factors of the grandmother hypothesis alone at different ages of menopause (2)

A
  • varying mother’s fertility enhancement due to grandmothers assistance
  • varying reduction in juvenile mortality due to grandmother’s asssitance
30
Q

what do female killer whales do after they undergo menopause

A
  • they become pod leaders with valuable survival skills
31
Q

AP theory: when would longer lifespan be selected for?

A
  • lower levels of predation could cause selection for longer life
  • would likely have negative effects on fecundity

ISCI 350 (14 decks)

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