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What is the adaptive value of parental care?

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6/12/08: Parental care

Lecture objectives:

1. Be able to apply a cost-benefit approach to the evolution of parental behavior

2. Understand the factors that influence the evolution of adoption and brood parasitism

3. Be familiar with types of parental favoritism, and be able to predict when parent-offspring conflict might occur as well as its outcome

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Parenthood, or taking care of offspring, is hard work

Mother's love worth $117,000 per year, study says

• Stay-at-home moms report working 94.4 hours per week

Male Tamarins lose up to ____________ while carrying infants

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There are benefits and costs to parental care

Benefits

Improved survival of offspring

Improved quality of offspring

Costs

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Species vary in how much parental care is given

Precocial: Altricial:

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Variation in amount of parental care is explained by costs and benefits of care

Hypothesis: birds adjust amount of parental care in relation to probability of survival

Predictions:

P1: N.A. more likely to care for offspring P2: S.A. more likely to care for self

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Variation in amount of parental care is explained by costs and benefits of care

Example: Nest defense by parent magpies

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Species vary in which parent provides the majority of care

Parental care in shorebirds

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Parental care is generally provided by females… Why?

Waterbug Randall’s jawfish Stickleback

…but not always… Why?

Benefits greater for females Costs greater for males

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Paternal behavior might evolve when males can ensure paternity

Hypothesis: Males are more likely to take care of young if they “think” they’re the dad

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Paternal behavior might evolve when costs are lower for males than for females

Do males pay a cost of parenting?Do females pay a cost of parenting?

Which gender pays the larger cost?

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To care for their young, parents must recognize their young

Mexican free-tailed bats

Many colonial species are good at offspring recognition

Adoption in Emperor penguins

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Juveniles sometimes seek adoption within their species

Gulls

Beg confidently

So why do parents allow adoption?

- Costs might be fairly low in some cases

- Offspring recognition is imperfect:If you ignore the begging of a stranger, you might accidentally ignore your offspring

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Parental deception: interspecific brood parasites

Cowbird in eastern phoebe nest Common Cuckoo in reed warbler nest

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Brood parasitism is common in cowbirds and cuckoos

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Size (relative to host nestlings) influences a brood parasite’s success

If hypothesis (above) is true, which chicks should have a higher survival?

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Why accept a parasite’s egg?1. Cost-benefit approach

Hypothesis: Warblers will be more likely to incubate parasite eggs if there are few new nest sites available

Removing an egg might be ____________________

Costs of abandoning a nest might be _____

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Why accept a parasite’s egg?2. Mafia Hypothesis

European great spotted cuckoo

If a parasite finds that its offspring have been harmed, it will

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Parental favoritism occurs when parents preferentially care for some offspring over others

Hypothesis: Parent coots preferentially feed babies with more orange feathers

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Some parents take favoritism to the extreme by allowing siblicide

Great egret Brown boobie

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Parent boobies can control siblicide to some extent

Masked booby(MB)

Blue-footed booby(BFB)

Tendency to prevent siblicide?

Tendency to allow siblicide?

What do you predict if offspring are in control? If parents are in control?

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Parent-offspring conflict occurs when the interests of parents and offspring are different

Example: amount of food to feed offspring

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Class discussion: parent-offspring conflict over siblicide(hypothetical example)

1. Is siblicide adaptive for the juvenile bird? (will siblicide increase its inclusive fitness?)

2. Is allowing siblicide adaptive for the parent bird?

2 offspring, each will have 3 surviving babies

If one bird commits siblicide, it will be able to have 5 surviving babies (but loses 3 nephews/nieces)

r (parent – offspring) = 0.5r (uncle/aunt – niece/nephew) = 0.25r (parent – grandoffspring) = 0.25