Lecture 17

Question 1

Parent-Offspring Conflict

Answer 1

• Offspring begs for food
• Parent provides food
• How much should offspring try to acquire?
• How much should parent provide?

Question 2

Trade-off

Answer 2

• B(p): fitness of focal offspring
• C(p): # of future offspring “given up”
• Maximize (benefit - cost)

Question 3

Offspring (benefits - cost)

Answer 3

• Gene that causes offspring to demand more resources will increase fitness through that offspring, but potentially reduce its fitness by losing out on future siblings
• Assuming sibling are genetically related, there is chance they would harbor this gene
• Assuming r = 1/2 (full siblings), then offspring should maximize B(p) - 1/2 C(p)

Question 4

Parent (benefits - cost)

Answer 4

• Gene that causes a parent to supply more resources will potentially increase its fitness through focal offspring and reduce it by losing out on future offspring
• Parents should maximize 1/2 B(p) - 1/2 C(p)

Question 5

Optimal provisioning rate is in conflict

Answer 5

• pp does not equal po

Question 6

Expect evolutionary conflict between parents and offspring over level of care

Answer 6

• Conflict can be resolved in many ways
• Parent wins
• Offspring wins
• Compromise

Question 7

Optimal provisioning in stitchbirds

Answer 7

• Stitchbird parents have to pay some attention to begging of offspring, but balance this with potential for future reproduction
• Do parents adjust allocation of resources to current offspring based on potential for future offspring?

Question 8

Examine resource provisioning to current brood by parents who are likely or unlikely to have a second brood in a season

Answer 8

• Part 1: Supplement adults with carotenoids (correlated with greater capacity to breed again)
• Part 2: Supplement offspring with carotenoids (correlated with increased intensity to begging signals)

Question 9

Results

Answer 9

• Intensity of a begging signal by offspring can increase provisioning by parents but only when costs of doing so are sufficiently low
• Stitchbirds show plasticity in provisioning rates and in their responses to offspring signals

Question 10

Why don’t all parents in wild desert leave their offspring immediately

Answer 10

• Benefits: increased quantity of offspring through re-mating
• Reduced quality of each offspring

Question 11

Thought experiment

Answer 11

• If benefit of deserting low for female and high for male. Cost of deserting high for female, low for male
• Benefit - cost of leaving are higher for males, so predict males more likely to desert
• If benefit - cost of leaving higher for females, predict females more likely to desert

Question 12

Kentish Plover Experiment

Answer 12

• Experiment 1(benefit of deserting:
  
  • Caught both parents on nest
  • One parent (either male or female) released
  • Measured time to re-mate
• Reasoning
  
  • Short time to re-mating -> high benefit for deserting
  • Long time to re-mating -> low benefit for deserting
• Experiment 2(costs of deserting):
  
  • Manipulate number of parents. Remove male, female, neither
  • Measure brood survival
• Reasoning:
  
  • Low rates of brood survival -> high cost for desertig
  • High rates of brood survival -> low cost for deserting

Question 13

Results

Answer 13

• Male have long time for relating, females have low time for remating
• High benefit for females, low benefit for males
• Experiment 2 results: Female have high brood survival, male have lower brood survival
  
  • Lower cost for female, high cost for males

Question 14

Balance of costs and benefits might be variable

Answer 14

• Benefit will change over course of the breeding season
• Cost will depend on size of brood

Question 15

Population of plovers where male care predominates

Answer 15

• Females should provide more care late in breeding season (benefit of deserting will be low)
• Females should provide more care to bigger broods (costs of deserting higher)

Question 16

Testing hypothesis 1

Answer 16

• Females adjust care over season as expected given reduction in potential benefits of deserting

Question 17

Testing hypothesis 2

Answer 17

• For brood hatched early in season: provide more care to bigger brood
• For brood hatched late in season: no influence on brood size, provide equal care

Question 18

Implications

Answer 18

• Level of female care is function of brood size and thus varies with cost of deserting
• Only when benefits of deserting are sufficiently high
• Kentish plovers show plasticity in parental care and their responses to brood size