BIO220H1 Lecture Notes - Lecture 10: Antagonistic Pleiotropy Hypothesis, Senescence, Pleiotropy

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7 Feb 2019
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WHY is there variation in rates of aging across species?
And WHY has aging evolved at all?!
Aging
§ Aging: proximate and ultimate causes
§ Costs of reproduction
§ The evolutionary theories of aging
§ Mutation accumulation
§ Antagonistic pleiotropy
What is aging or senescence?
Definition:
Progressive decline in somatic function reflected in reductions in fertility as well as
survivorship
Proximate cause:
Progressive degeneration of the soma
Manifestations of aging
General degeneration of the soma
Impaired function (speed, strength, sight, etc)
Increased disease (cancer, organ failure)
Mortality rate increases with age
Senescence:
An evolutionary mystery
Intuition would suggest:
aging seems to be non-adaptive in the extreme
Which leads to the question:
Why do aging mechanisms exist at all?
One proximate theory of aging
Oxidative metabolism produces highly reactive free radicals that damage
macromolecules (DNA, protein, lipids) in our bodies.
Vitamins E and C can act as antioxidants.
But, this theory also raises some questions.
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We have our own defenses and repair mechanisms (e.g., various amino acids act as
antioxidants), so
***Why not “enoughrepair?!***
CONSTRAINST!
Trade-offs affect the evolution of all traits
Display size (morphological trait)
Foraging rate (behavioural trait)
Longevity, aging (life history trait)
Trade-offs may govern the evolution of DNA repair mechanisms?
+: longevity
-: Fecundity (energetically cost, limited resources)
Costs of reproduction?
If yes, then high reproductive rates will accelerate senescence and thereby shorten life
span
+: reproductive rate (good for natural selection)
-: longevity
Reproductive costs in waterstriders
Prediction:
Females induced to reproduce at a high rate will have reduced longevity
(more food, more offspring, decreased longevity)
Test: female waterstriders
Hypothesis:
High reproductive rates accelerate senescence and thereby shorten life span
Design:
Manipulated reproductive rate of females by changing food abundance
Data:
Reproductive rate (# of eggs), longevity, quality of eggs
Senescence of the mother can be seen in age-related declines in the quality of her eggs.
Normal development, developmentally arrested, abnormal development
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