Parental Care

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Parental Care

• Patterns
• Who should provide care?
• How much care should be provided?
• When should care be terminated?
• Who should receive care?

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Insect parental care
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Distribution of parental care in vertebrates

• Teleost fishes 21 of families show PC
• 61 have male parental care
• Amphibians 71 show PC
• 5050 maternalpaternal
• Birds 100 show PC
• Usually biparental, sometimes one sex
• Mammals 100 show PC
• Usually maternal, sometimes biparental

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Alternative hypotheses for providing care

• Confidence of paternity
• Expect parent with highest certainty to be
  parental
• Order of gamete release
• First to deposit gametes can desert
• Association
• Sex nearest to offspring when care is needed

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Parental care in fishes and frogs
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Alternative hypotheses for providing care
evidence

• Confidence of paternity (fish and herps)
• Internal fertilization - 86 maternal care
• External fertilization - 70 paternal care
• Order of gamete release
• Simultaneous fertilization (most species) - 78
  paternal
• Other species - male deposits first, but doesnt
  leave
• Association (fits data the best)
• Territorial males have external fertilization

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Two or one parents?

• Birds and mammals are more likely to exhibit
  biparental care because parents feed young and
  two are often better than one
• Fishes and amphibians typically only guard eggs
  and dont feed young. One parent usually can do
  this as well as two.
• Exceptions include some cichlids that show
  biparental care

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Why male only parental care?
Seahorse
Randalls jawfish
Stickleback
Mallee fowl
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Parental care can cost females more than males
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Growth, fecundity and paternal care
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How much care to provide?

• Parental investment any investment by the
  parent in an individual offspring that increases
  the offsprings chance of surviving at the cost
  of the parents ability to invest in other
  offspring (Trivers 1972)
• Costs of parental care include
• Reduced future survival
• Reduced mating opportunities

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Parental care can decrease adult survival
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Parental care decreases mating opportunities
A female-biased sex ratio increases the cost of
brood care for males because parental care
detracts from mating
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Parental investment changes over time
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Parent-offspring conflict
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Parent-offspring conflict
Wallaby conflict

• Assume fixed total resource that can be used to
  feed offspring
• Parents want to distribute resource equitably to
  all n offspring
• Offspring want more than 1/n but not all since
  they are related to siblings
• Difference between parent and offspring optimum
  increases as relatedness decreases

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Parent-offspring conflict how much care to
provide
Parent is equally related to all offspring,
but offspring are less related to sibs than
themselves. Assuming full siblings, i.e. r 1/2
B - measured in units of RS of current
offspring C - measured in - units of RS of future
offspring
B
C
Benefit or cost to parent
Level of parental investment
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Begging loudness increases as relatedness within
nest decreases
Brown-headed cowbird
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Parent-offspring conflict time of weaning
(Full-sibs)
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Parental investment and maternal age
If reproductive value declines with maternal age,
then older females should be willing to expend
more on parental care
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Who should receive care?

• Concorde fallacy past investment should not
  determine future investment - only prospects for
  future success
• Expect parents to use honest indicators of
  offspring quality to allocate care

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Chick color affects parental care in mixed broods
of coots
Control broods were unaltered (orange) or had
orange feathers trimmed (black) Experimental
broods had 1/2 orange, 1/2 black chicks
Chick color likely indicates offspring health
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Sibling competition
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Sibling conflict