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Chapter 13 Aging and Other Life History Characteristics.

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Presentation on theme: "Chapter 13 Aging and Other Life History Characteristics."— Presentation transcript:

1 Chapter 13 Aging and Other Life History Characteristics

2 Life History Analysis: Study of Reproductive Strategies Reproduce early & fast or later & slow? – Deer mice mature at 7 weeks, have litters 3-4 times/year – Black bears mature at 4-5 years and have cubs every 2 years Range of lifespans: single season to years – California poppy flowers & dies yearly (annual) – Black cherry flowers yearly for decades (perennial) Reproduce lots of little eggs or a few large ones? – Oysters (10-50 million eggs @ 55 µm) – Clams (<100 eggs @ 300 µm)

3 Sockeye Salmon Will defend egg nests as long as they have enough energy to stay alive Laying eggs earlier in life requires less energy, fish live longer Also better able to defend nest

4 Thrips Eat Their Way Out (of Mom)

5 Brown Kiwis Lay Extreme Eggs


7 An Example of Life History: Opossum

8 Life History Tradeoffs Short-winged female Hatch with poorly- developed flight muscles & lower triglyceride levels Use that energy to make phospholipids for eggs Reproduce earlier Long-winged female Hatch with well-developed flight muscles & loads of triglycerides (flight fuel) Some can fly: may enable her to seek better environment Ovaries grow more slowly

9 Why do Organisms Age and Die? Senescence refers to a late-life decline in fertility and survival Should be opposed by natural selection Two theories: 1.Rate-of-living theory: populations lack sufficient genetic variation to keep evolving longer lifespans: irreparable damage to cells/tissues 2.Evolutionary theory: tradeoff between directing energy to reproduction versus repair/survival

10 Costs of Aging

11 Rate-of-Living Theory Damage to cells/tissues occurs during replication, transcription, translation, accumulation of toxic metabolic by-products Two predictions: 1.Aging rate should be correlated to metabolic rate 2.Species should not be able to evolve longer lifespans due to selection (natural or artificial)

12 Does Aging Rate=Metabolic Rate?

13 Aging & Mutation

14 Can Lifespan Change or Evolve? Researchers artificially selected for longevity Unclear if metabolic rate also contributed

15 Hayflick Limit & Telomeres Caps on the ends of chromosomes – Kinda like aglets – Sequence TTAGGG Shorten with each cell division – When too short, cells stop dividing – Eventually die: part of aging Only stem cells, cancer cells, germ cells exempt

16 Telomere Length & Lifespan

17 Altering Lifespan

18 The Evolutionary Theory Recap: Tradeoff between self-maintenance and reproduction Aging caused by failure to FULLY repair damage: slower path to death 2 reasons: 1.Deleterious mutations 2.Trade-offs between repair and reproduction

19 Basic Model for Evolution of Aging Critter lives 16 years 80% chance of survival year-to-year Sexual maturity at age 3 One offspring/year Overall expected reproductive success is 2.419

20 Effect of Deleterious Mutation Mutation causes early death at 14 years NO other alterations Overall expected reproductive success is 2.340 Slightly reduced relative to WT population (not a big change in survival): WEAK SELECTION

21 Tradeoff: Reproduction vs. Death 2 mutations 1.Lifespan decreased to 10 years (should lower overall success) 2.Maturation reduced to 2 years rather than 3 (should increase overall success) Overall expected reproductive success is 2.663 Moderate increase relative to WT: OFFSETS SOMEWHAT STRONGER SELECTION

22 Mutation Accumulation Reduced fitness in small populations (inbreeding depression) may be due to accumulation of deleterious mutations Longevity in small populations declines faster for late-acting deleterious genes (neutral)

23 Tradeoffs: Reproduction vs. Stress Resistance Normal flies die younger but reproduce better; methuselah flies live longer but reproduce less: TEMPERATURE DEPENDENT EFFECT

24 Antagonistic Pleiotropy One gene affects 2 traits: longevity & survival If beneficial, should increase; if deleterious, should decrease Hx546 increases longevity: deleterious when food is scarce (right)


26 Optimal Clutch Size Lacks hypothesis: Average clutch size should equal optimal size

27 Optimum Clutch Size for Great Tits Optimal=12, Average=8. Violates Lacks hypothesis.

28 Family Size Affects Next Generation Researchers added or removed eggs from nest The daughters compensated in the next generation Suggests a quality vs. quantity tradeoff – Daughters produce more eggs if they got more care

29 Lacks Hypothesis & Parasitoid Wasps SpeciesOptimalActual Anagasta41-2 Ellopia75-8 Bupalus95-8



32 Size vs. Quantity Tradeoff

33 The Optimal Compromise… for Everyone SMITH-FRETWELL hypothesis: More offspring decreases fitness of offspring Bigger size increases fitness of offspring PARENTAL fitness is better for smaller clutches

34 Testing Smith-Fretwell Larger clutches of small eggs: CONFIRMED Larger eggs have better survival: CONFIRMED Parental fitness: intermediate clutches of intermediate eggs: CONFIRMED – Drops in hatcheries due to safer environment


36 Phenotypic Plasticity What role does environment play in egg size? – Good host/environment, smaller eggs & more of them – Poor host/environment, larger eggs & fewer of them

37 Phenotypic Plasticity Acacia tree is a good host More eggs laid Cercidium tree is a poor host Fewer eggs laid If you change hosts: Good Poor: egg size increases Poor Good: egg size decreases

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