Parental Care Patterns Who should provide care? How much care should be provided? When should care...

Parental Care

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

Insect parental care

Distribution of parental care in vertebrates

• Teleost fishes = 21% of families show PC– 61% have male parental care

• Amphibians = 71% show PC– 50:50 maternal:paternal

• Birds = 100% show PC– Usually biparental, sometimes one sex

• Mammals = 100% show PC– Usually maternal, sometimes biparental

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

Parental care in fishes and

frogs

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 doesn’t leave

• Association (fits data the best)– Territorial males have external fertilization

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 don’t feed young. One parent usually can do this as well as two.– Exceptions include some cichlids that show

biparental care

Why male only

parental care?

Randall’s jawfish

Mallee fowlStickleback

Seahorse

Parental care can cost females more than males

Mouthbrooding results in weight loss due to reduction in feeding,and the cost of brood care is higher in females than males

Growth, fecundity and paternal care

How much care to provide?

• Parental investment: “any investment by the parent in an individual offspring that increases the offspring’s chance of surviving at the cost of the parent’s ability to invest in other offspring (Trivers 1972)

• Costs of parental care include– Reduced future survival– Reduced mating opportunities

Parental care can decrease adult survival

Parental care decreases mating opportunities

A female-biased sex ratio increases the cost of brood care for males because parental care detracts from mating

Parental investment changes over time

Parent-offspring conflict

Parent-offspring 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

Wallaby conflict

Parent-offspring conflict: how much care to provide

Parent is equally relatedto all offspring, butoffspring are less relatedto sibs than themselves.Assuming full siblings,i.e. r = 1/2

Level of parental investment

Benefit or cost to parent

B

C

Max. inclusive fitnessfor parent

C/2

Max. inclusive fitnessfor offspring

B - measured in +units of RS of current offspringC - measured in - units of RS of future offspring

Begging loudness increases as relatedness within nest decreases

Brown-headed cowbird

Parent-offspring conflict: time of weaning

(Full-sibs)

(Half-sibs)

Parental investment and maternal age

If reproductive value declineswith maternal age, then olderfemales should be willing toexpend more on parental care

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

Chick color affects parental care in mixed broods of coots

Control broods were unaltered(orange) or had orange featherstrimmed (black)Experimental broods had1/2 orange, 1/2 black chicks

Chick color likely indicatesoffspring health

Sibling competition

Sibling conflict