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3s1: Evolution of health and disease > Week 2 > Flashcards

Week 2 Flashcards

1
Q

What things are investigated in life history traits?

A

Size at birth, growth rate, age and size at sexual maturity, number offspring, size and sex ratio, age- and size-specific reproductive investment and mortality schedule, lifespan

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2
Q

What is R0?

A

Lifetime expectation of female offspring; net reproductive rate

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3
Q

How do you calculate R0?

A

sum of lxmx
lx = survival to age x
mx = birth rate

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4
Q

What does life history maximise?

A

maximises r, intrinsic rate of increase, or Malthusian parameter

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5
Q

What does Euler-Lotka equation calculate?

A

r (fitness) related to history parameters (survival probability and fertility)

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6
Q

What is an example of an event history diagram showing how lifespan and fecindity are related?

A

Wildtype - 0.75 dead by day 18 but producing 100 + eggs for 3 days
Daf-2 - 0.25 dead by day 18 but only 1 day are 100+ eggs produced
Trade off both produce same amount of eggs but wt are earlier but dont live as long

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7
Q

Why do trade offs occur in nature?

A

Constraints prevent life history variables leading to high r from being simultaneously maximised

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8
Q

What are hypothetical examples of trade offs?

A

Traits that increase r might make the organism more vulnerable to ecological hazards (predation, parasitism)

May be constraints that put limits on what can be achieved (reproduction vs lifespan)

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9
Q

What important trade offs in nature?

A

Current reproduction and survival
Current and future reproduction
Number, size and sex of offspring
Reproduction and immune status

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10
Q

What is a trade off between nursing and mortality rate?

A

Nursing roe deer have increased mortality rate per year, increasing with age
Non nursing mothers dont have an increase in mortality rate except at 14 years old

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11
Q

What is an example of human familes and the data used for life to child impact?

A

Finland lutherans n = 22,000 people
Strict Lutherans - Required to submit accurate censuses,
1700s-1900; low paternity outside marriage
2200 families average family size ~6; 60% surviving to adulthood, ~80-90% followed until death

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12
Q

What was the link between maternal longevity with child in the Lutherans Fins?

A

Mothers life expectancy decreases with more sons
Negligable change in life expectancy with more daughters

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13
Q

How are physiological trade offs measured?

A

Phenotypic manipulations
Genetic manipulations
Phenotypic correlations

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14
Q

What is an example of phenotypic manipulations?

A

Manipulations that extend lifespan also reduce reproduction

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15
Q

What is an example phenotypic manipulation in primates?

A

Macaques > 27 years old (old)
Calorie restricted diet - CR is adequate nutrition on 30 percent fewer calories

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16
Q

What was the outcome of calorie resticted diet in Macaques?

A

CR diet - lower levels of cancer, diabetes, heart disease, brain atrophy and lean-muscle loss

5/38 CR monkeys died from age-related causes 14/38 controls

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17
Q

What is an example of genetic manipulations for measuring trade offs?

A

Genetic manipulation of reproductive pathways (e.g. removal of germ line & nutrient sensing) leading to extended lifespan

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18
Q

What was an experiment genetic manipulation for measuring impacts of lifespan?

A

Drosophilia melanogaster - remived germ line cells
Both male and female flies that have germ line cells removed lived longer than wildtype

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19
Q

What is an example of phenotypic correlations for measuring trade offs?

A

Measurements on un-manipulated individuals e.g negative associations between offspring and lifespan

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20
Q

What is an example of phenotypic correlations for impact on lifespan?

A

The Lutharan finnish women (more sons lower maternal longevity, dughter had a minor impact)

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21
Q

What are the problems with phenotypic correlations?

A

This approach cannot directly demonstrate causality
Most / all work on humans is correlational

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22
Q

How can you measure evolutionary trade offs?

A

Direct and correlated responses to artificial selection

23
Q

How did they place an artificial selection on Drosophila lifespans?

A

Select flies that bred either young or old across 6 generations

24
Q

What where the results for the artifical selection on drosophila?

A

Direct response: short and long lived flies
Correlated response long lived females produced fewer progeny (potentially shows trade off between lifespan and fertility)

25
Q

Why are trade offs important?

A

human health suggests that we ‘can’t have it all’ many constraints on what can be achieved

26
Q

What determines the timing of reproductive maturity?

A

Balance between mortality risk against fertility

27
Q

What determines survival to reproductive age?

A

Risk (‘danger’, disease, stress)
Nutrition

28
Q

What is a summery of fertility as a function of size?

A

Growth / nutrition

29
Q

What is a prediction if survival to maturity is low?

A

Early sexual maturation is favoured by natural selection

30
Q

What is a prediction when subsequent annual survivial is low?

A

‘One shot’ reproduction favoured by natural selection

31
Q

What are prediciotn of fertility related to growth/food?

A

Earlier sexual maturation when food abundant
Later sexual maturation when food limiting

32
Q

Why is expected age at reproduction plastic?

A

Depending on mortality risk versus fertility (food / growth)

33
Q

What experimental evidence for plasticity in timing of reproductive maturity?

A

Group of daphnia put in tank which had contained a fish predator (fish treatment) and then measured the reproductive response

34
Q

What were the results for the daphnia in fish treatment tank vs control?

A

Treatment group:
Reached sexual maturity earlier
Were smaller at sexual maturity
Had larger broods at earlier age
This showed that they can read conditions and adjust growth and reproductive accordingly

35
Q

What is evidence of reproductive maturity in humans?

A

22 groups of non-industrialised humans:
Age at menarche positively related to survival and life expectancy to age 15
Age at first female reproduction positively related to survival to age 15
All show negative relationship with body size

36
Q

What is the relationship between body size and survivorship?

A

Sexual maturity related to body size and survivorship – but opposing forces
Balance of these two opposing forces determines optimum age at first reproduction

37
Q

What is an example if age of sexual maturity modelled?

A

Modeled optimal age at sexual maturity in Ache hunter-gatherers
Used mortality data, growth rate and body size

38
Q

What is the relationship between body size and fertility for ache hunter gatherers?

A

Females - positive relationship between fertility and weight
Males - positve relationship between fertility and weight until 65kg where it then decreases

39
Q

What is the probability of death with age for ache hunter gatherers?

A

Both start high, quickily drop stabilising ay a low level before increasing with age. Males slightly higher than females particually arounf middle to early old age

40
Q

What is Hill and Hurtado’s model of optimal age of sexual maturity?

A

Optimal age at maturity at bottom axis
With survival to maturity and potential fertility at maturity (due to body size) overlayed
Optimum = bold solid line (where the 2 lower lines cross)

41
Q

What happens to Hill and Hurtado’s model when survival is lower?

A

If survival is lower (you drop the la line lower), then the lines cross earlier, meaning optimal age at maturity will be lower and vice versa

42
Q

How well does Hill and Hurtado’s model work?

A

Pretty well. Model 1 was 1.5 years off, model 2 was better (models 1 and 2 adopt different ways of calculating expected fertility as a function of age and weight)

43
Q

In what other case studies did Hill and Hurtado model work?

A

spot on for !kung hunter-gatherers
Successfully predicts earlier menarche for white women from the US (controversal use for prediciting women in USA)

44
Q

Why have animals evolved reactionairy reproduction?

A

Enables expression of optimal age at sexual maturity according to specific aspects of environment, e.g. mortality risk

45
Q

What evidence is there for perceived mortality risk associated with age at first reproduction?

A

Wilson & Daly 1997 - US neighbourhoods with the lowest life-expectancy have the highest teenage pregnancy rates.
Suggests: Women who perceive themselves to be in a risky environment may reproduce earlier

46
Q

What is the link between reproduction and risk?

A

Optimal age at reproduction can be predicted - From size / fertility and mortality risk data
Risk, perceived or actual varies between individuals and groups - Associated with age at sexual maturity

47
Q

What are the found levels of testosterone?

A

Found at higher levels than ‘required’ for spermatogenesis and sexual functioning

48
Q

What are the trade offs with elevated testosterone?

A

Immunosuppressive
Behaviour - higher ‘future discounting’
Higher risk of prostate and testicular cancer
Males more costly or ‘difficult’ to produce?
Higher mortality; female > male lifespan

49
Q

Why do males express higher levels of testosterone?

A

Males that ‘display’ high testosterone show they can thrive despite its costs
Cannot be ‘faked’ by lower quality individuals

50
Q

What are the predicitions if the handicap hypothesis is correct?

A

Males who display high testosterone should:
be more attractive to females?
have higher mating success?
possess other traits that signal high quality?

51
Q

How is testosterone displayed?

A

At sexual maturity:
The chin becomes longer
The vertical ramus becomes flared
Eye socket height decreases, brow ridges develop

52
Q

Is there a preference for masculine/ high testosterone faces?

A

No clear preference for facial testosterone, from several studies
Except, perhaps, when associated with specific sexual strategy (SOI) score

53
Q

Why is there no clear preference for facil testosterone?

A

Sometimes preferences associated with phase of the menstrual cycle
Women in modern societies have different hormonal profiles across the menstrual cycle cf women in anthropological studies, or in our evolutionary past

54
Q

What is the testosterone and male quality?

A

Phenotypic correlation
Men with higher facial testosterone report fewer illnesses

3s1: Evolution of health and disease (10 decks)

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