senescence
- late-life decline in fertility/survival
‘rate of living’ theory of aging (4)
- type of theory
- reason for senescence
- evolution of organism lifespan
- do we need to explain senescence?
- 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
predictions of ‘rate of living’ theory (2)
- 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
why is the ‘rate of living’ theory incorrect (2)
- selection for longer life spans should not be possible, but it is
- wear and tear alone is not sufficient to explain senescence
assumptions of the ‘rate-of-living’ theory that are testable (2)
- 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
do we need to explain senescence? (2)
- 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
reasoning behind evolutionary theories of senescence: older age class representation in populations
- older age classes less represented in populations due to constant risk of death from accidents, predators, etc
reasoning behind evolutionary theories of senescence: how does selection act on deleterious alleles of late expression vs early expression (2)
- 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
according to the evolutionary theories of aging, what is the senescence the consequence of?
- senescence is an inevitable consequence of the fact that the strength of natural selection declines with age
mutation accumulation hypothesis (2)
- type of evolutionary theory
- hypothesis
- 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
antagonistic pleiotropy hypothesis (2)
- type of evolutionary theory
- hypothesis
- evolutionary theory of aging
- germ-line deleterious mutations expressed late in life are selected for if they increase fitness early in life
mutation accumulation hypothesis assumption
- relative fitness of alleles will likely decrease in late life as these alleles are not selected as strongly for
mutation accumulation hypothesis prediction
- effect of inbreeding depression is expected to increase with age
antagonistic pleiotropy hypothesis assumptions (3)
- 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
antagonistic pleiotropy hypothesis prediction (3)
- 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
genes with pleiotropic effects (3)
- immune systems chemicals
- gene for iron absorption
- p53 tumour suppressor protein
how do immune system chemical have pleiotropic effects (2)
- chemicals protect from infection
- chemicals also damage host tissues
how does the gene for iron absorption have pleiotropic effects
- protects from iron deficiency anemia (especially in menstruating women)
- may contribute to death in middle age due to excess iron absorption (hemochromatosis)
how does p53, a tumour suppressor gene have pleiotropic effects
- signals cells to stop dividing when damaged
- may cause stem cells to stop dividing prematurely
telomeres (3)
- benefit
- concern
- prevention
- 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
the problem of menopause (2)
- 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
humans compared to other primates (3)
- age at weaning
- development
- lifespan
- reduced age of weaning
- extended development
- lengthened lifespan
non-adaptive hypotheses of menopause (2)
- phylogenetic inertia
- artifact of modern lifestyle
adaptive hypotheses of menopause (3)
- mother hypothesis
- ‘grandmother’ hypothesis
- reproductive competition between generations
