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13.1Parental care varies among species and
reflects life history trade-offs
• Parental care
– Activities of an adult that enhance the
survivorship of offspring
• Life history traits
– Traits involved with growth, reproduction, and
survivorship that are the result of natural
selection
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
Life history trade-offs
• Natural selection will favor the evolution of
behaviors that maximize an individual’s lifetime
reproductive success
• Energy (effort) is limited: effort allocated to
reproduction reduces effort that can be
allocated to an individual’s growth and
survivorship
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
Life history trade-offs
• Across species, we often see the evolution of
life history traits
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
Featured Research
Life history variation in fish
• Research question: How do life history traits
vary among fish? (Vila-Gispert, MorenoAmich, & García-Berthou 2002)
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
Featured Research
Life history variation in fish
• Methods:
– Obtained life history data for 300 species,
including age at maturity, maximum body size,
length of breeding season, number of reproductive
events per year, average egg size, fecundity, and
level of parental care
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
Featured Research
Life history variation in fish
• Results:
– Species with larger body
size tended to have later
maturation, larger eggs,
fewer reproductive events
per year, and higher levels
of parental care
– Small species showed the
opposite trends
• Conclusion:
– These patterns reflect
basic life history trade-offs
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
Variation in parental care
• Species vary in parental care provided
• In some species:
– Only females provide care (maternal care)
– Only males provide care (paternal care)
– Both species provide care (biparental care)
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
13.2 Sexual conflict is the basis for sexbiased parental care
• In many species, females provide
more parental care than males.
Why?
• Sexual conflict: each sex has
different benefits and costs of
providing care
• Males tend to be less certain of
offspring paternity so they have a
higher cost of providing care
(care for unrelated individuals)
– This favors the evolution of
reduced care by males
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
Featured Research
Paternity uncertainty and parental care in
boobies
• Research question: Do males vary the level of
care within a clutch of offspring? (OsorioBeristain & Drummond 2001)
• Hypothesis: Certainty of paternity affects a
male’s level of care
• Prediction: Males will provide low care when
certainty of paternity is low
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
Featured Research
Paternity uncertainty and parental care in
boobies
• Methods:
– Blue-footed booby (Sula nebouxii)
– Manipulated certainty of paternity by removing
pair-bonded males for 11 hours when their mate
was fertile
– Control males were removed for 11 hours when
their mate was not fertile
– Observed behavior of males when they returned
to their mate
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
Featured Research
Paternity uncertainty and parental care in
boobies
• Results:
– 7 of 16 experimental males
removed the first egg laid
by their mate from the nest
– No control males removed
eggs from the nest
• Conclusion:
– Certainty of paternity
affects level of paternal care
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
The evolution of male-only care
• Birds and mammals have internal fertilization and
determinate growth, while many fishes have external
fertilization and indeterminate growth
• Larger females can produce more eggs, so parental
care is now more costly to females; providing care
limits growth and future fecundity
• External fertilization increases certainty of paternity
for males: this lowers the cost of care
• For fishes, the higher costs of care for females and
lower costs of care for males can favor the evolution
of male-only care
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
Featured Research
Paternity assurance and male care in water
bugs
• Research question: Why
do water bugs have maleonly care despite having
internal fertilization and
sperm storage by
females? (Smith 1979)
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
Featured Research
Paternity assurance and male care in water
bugs
• Methods:
– Giant water bug (Abedus herberti)
– Observed mating behavior
– Experiment 1: Female mated with one male but was
not allowed to oviposit. After several weeks she
mated with the second male and oviposited eggs on
his back
– Experiment 2: On day 1, the female mated with one
male and oviposited eggs on his back; on day 2, she
mated with the second male and oviposited on his
back. This was repeated for several days
– Recorded the paternity of the offspring on the
second male’s back
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
Featured Research
Paternity assurance and male care in water
bugs
• Results:
– Experiment 1: For 20 of 25 males, the second male
fertilized 100% of the eggs on his back
– Experiment 2: 245 of 250 offspring were sired by
the male who carried the eggs
• Conclusion:
– Male water bugs have a high degree of certainty of
parentage despite having internal fertilization
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
13.3 Hormones regulate parental care
• Many animals undergo a radical change in
behavior during the breeding season
• Early on, they concentrate on finding and
attracting mates
• Later, they concentrate on providing care to
offspring
• Prolactin levels in vertebrates vary over the
reproductive season
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
Featured Research
Prolactin and maternal care in rats
• Research question: Does
prolactin affect parental
care? (Bridges et al.
1990)
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
Featured Research
Prolactin and maternal care in rats
• Methods:
– Manipulated prolactin levels in female rats
– All females were “primed” with progesterone and
estradiol to mimic changes in these steroid
hormones during pregnancy
– Compared behavior of females treated with either
prolactin or control (sodium chloride–sodium
bicarbonate)
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
Featured Research
Prolactin and maternal care in rats
• Results:
– Females injected with
prolactin exhibited higher
levels of care than controls
– Females not primed with
steroid hormones exhibited
little care
• Conclusion:
– Prolactin strongly affects
parental care behavior
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
Featured Research
Prolactin and incubation in penguins
• Research question: In birds, what causes
prolactin levels to increase during egg laying?
(Massaro, Setiawan, & Davis 2007)
• Hypothesis 1: The sight of eggs stimulates
prolactin production
• Hypothesis 2: Tactile stimulation (brood patch
contact with eggs) stimulates prolactin
production
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
Featured Research
Prolactin and incubation in penguins
• Methods:
– Yellow-eyed penguins (Megadyptes
antipodes)
– Sampled prolactin levels
– Group 1: Sampled before an
artificial egg was added to the nest
– Group 2: Sampled three to four
days after artificial egg added to
their nest (visual and tactile cues)
or next to the nest (visual cues
only)
– Group 3: Sampled at the same time
as Group 2, but no egg was added
to their nest (control)
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
Featured Research
Prolactin and incubation in penguins
• Results:
– Birds that could only see eggs did
not have elevated prolactin levels
– Birds that had eggs added to the
nest had higher prolactin levels
than controls
• Conclusion:
– Visual cues and tactile stimulation
result in increased prolactin
production in these birds
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
Featured Research
Juvenile hormones and parental care in
earwigs
• In insects, juvenile hormone
(JH) affects development and
molting and also varies over
the reproductive cycle and
with levels of parental care
• Research question: Does JH
affect parental care? (Rankin,
Fox, & Stotsky 1995)
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
Featured Research
Juvenile hormones and parental care in
earwigs
• Methods:
– Ring-legged earwigs (Euborellia annulipes)
– Topically added JH in acetone to female
– Controls were either untreated or treated only
with acetone
– Measured duration of egg care
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
Featured Research
Juvenile hormones and parental care in
earwigs
• Results:
– Females with JH added
showed the least amount
of egg care
• Conclusion:
– JH affects parental care:
high levels of JH result in
low care and vice versa
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
13.4 Parental care involves fitness tradeoffs between current and future
reproduction
• The benefit of parental care is enhanced
survivorship of young
• The costs of providing parental care involve
reductions in both current and future
reproduction
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
Featured Research
Predation risk and parental care in
golden egg bugs
• Research question: How does parental care
affect an adult’s predation risk? (Reguera &
Gomendio 1999)
• Hypothesis: Providing care for eggs can
increase predation risk
• Prediction: Males caring for eggs will
experience higher mortality from predators
than males not caring for eggs
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
Featured Research
Predation risk and parental care in
golden egg bugs
• Methods:
– Golden egg bugs (Phyllomorpha laciniata)
– Placed four adult males in an aviary with two bird
predators
– Two males carried eggs on their backs (parental
care); two males did not carry eggs
– Recorded the last bug alive in the aviary
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
Featured Research
Predation risk and parental care in
golden egg bugs
• Results:
– In 10 of 11 trials, the last bug alive
was one that did not carry eggs
• Conclusion:
– Providing care for eggs by carrying
them enhances the risk of
predation for an adult
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
Featured Research
Predation risk and parental care in
golden egg bugs
• Research question: Given the cost, why do
golden egg bug males carry eggs? (Reguera &
Gomendio 2002)
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
Featured Research
Predation risk and parental care in
golden egg bugs
• Methods:
– Characterized survivorship of eggs laid on plants and
eggs carried by adults
– Examined variation in egg carrying across
populations
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
Featured Research
Predation risk and parental care in
golden egg bugs
• Results:
– Eggs laid on plants had a 3%
survival rate (high predation on
eggs via egg parasitism)
– Eggs carried by adults (mostly
males) had 25% survival rate
– Egg carrying was most common
in populations with high rates of
egg parasitism
• Conclusion:
– Providing care for eggs by
carrying them enhances offspring
survivorship
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
Featured Research
Egg guarding and opportunity costs
of parental care in frogs
• Research question: If egg-guarding parental
care increases offspring success, why don’t all
males attend eggs at a high level? (Cheng &
Kam 2010)
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
Featured Research
Egg guarding and opportunity costs
of parental care in frogs
• Methods:
– Big-thumbed frogs (Kurixalus
eiffingeri)
– Uniquely marked males as they
tended eggs
– Egg masses were quantified
and egg mortality noted
– Male attendance was recorded
each night over six days
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
Featured Research
Egg guarding and opportunity costs
of parental care in frogs
• Results:
– Egg mortality was negatively correlated with male attendance
– Male attendance was positively correlated with egg mass clutch size
• Conclusion:
– Males with small clutches may be searching for additional mating
opportunities
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
Parent-offspring conflict theory
• Parent-offspring conflict theory – parents and
their dependent offspring are under different
selection pressures:
– Parents should maximize their lifetime reproductive
success
– Offspring should maximize the energy and
protection they receive from parents to survive to
reproductive age
• Parental investment
– Any investment by parents in an offspring that
increases offspring survival at the cost of the
parent’s ability to invest in other offspring
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
Parent-offspring conflict theory
• The optimal level of
parental investment is
always higher for
offspring than for a
parent
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
Featured Research
Parental care trade-off in
treehoppers
• Research question: Within a species, why is
there much variation in parental care such as
egg guarding? (Zink 2003)
• Hypothesis: There is a trade-off between
current and future reproduction
• Prediction 1: Egg guarding will increase egg
survival (current reproduction)
• Prediction 2: Increased egg guarding will
decrease future reproduction
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
Featured Research
Parental care trade-off in
treehoppers
• Methods:
– Tree hoppers (Publilia concava)
– Marked individual females that
had deposited an egg mass
– Noted number of days they
guarded the eggs
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
Featured Research
Parental care trade-off in treehoppers
• Results:
– Egg hatching success was
positively correlated with
female egg-guarding
duration
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
Featured Research
Parental care trade-off in treehoppers
• Results:
– Females that guarded a clutch
for more than ten days had
fewer and smaller future
broods than females that
spent less time egg guarding
• Conclusion:
– Parental care (egg guarding)
enhances current
reproductive success but at a
cost of future reproduction
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
Applying the Concepts
Applying the Concepts 13.1
Smallmouth bass defend their nest from exotic predators
• Exotic predators can reduce
population size of native
species
• Exotic egg predators in Lake
Erie increase the cost of
parental care (egg guarding) for
smallmouth bass (Micropterus
dolomieu)
• This increased energy demand
of care will likely reduce the
lifetime fitness of bass and
could lead to population
decline
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
Brood reduction and parent-offspring
conflict
• Brood reduction
– Differential offspring mortality, often within a single
clutch
• Theory predicts that brood reduction can be
adaptive for a parent by reducing its cost of
current reproduction and so enhancing
survivorship and future reproduction
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
Featured Research
Brood reduction in fur seals
• Research question: Why do females give birth
in consecutive years? (Trillmich & Wolf 2008)
– Some marine mammals give birth in consecutive
years, but pups are not weaned for two years.
Lactation costs are high for a female with two
pups, and the younger pup rarely survives (brood
reduction occurs)
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
Featured Research
Brood reduction in fur seals
• Hypothesis: The
survivorship of young with
an older sibling is related to
resource availability
• Prediction: The second
offspring will suffer high
mortality in years of scarce
resources and have high
survivorship in years of
abundant resources
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
Featured Research
Brood reduction in fur seals
• Methods:
– Galápagos fur seals (Arctocephalus galapagoensis)
– Marked both unweaned older pups and their
younger siblings
– Recorded the survivorship of younger siblings
– Estimated food availability using sea surface
temperature (cold-water years have high food
abundance while warm-water years have low food
abundance)
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
Featured Research
Brood reduction in fur seals
• Results:
– Survival of younger pups
was related to water
temperature (food
availability)
• Conclusion:
– Brood reduction (pup
death) is a function of
food availability. Parents
can raise pups in
consecutive years when
food availability is high,
but this cannot be
predicted in advance
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
Applying the Concepts
Applying the Concepts 13.2
Food supplementation reduces food reduction in
endangered eagles
• Brood reduction is common in
birds of prey
• Conservation biologists are
trying to increase the
population of the endangered
Spanish imperial eagle (Aquila
adalberti)
• Food supplementation has
increased survivorship of
second offspring (reduced
brood reduction)
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
Brood parasitism
• Brood parasitism
– Female lays an egg in the nest
of another female
• Reduces the cost of parental
care (another female raises
the young)
• Brood parasites can lay all
(pure parasite) or some eggs
(nesting parasites) in the nest
of another female
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
Featured Research
Conspecific brood parasitism in
ducks
• Research question: What reproductive
strategy leads to the highest fitness (pure
parasite, nesting parasite [mixed strategy], or
nonparasites)? (Åhlund & Andersson 2001)
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
Featured Research
Conspecific brood parasitism in
ducks
• Methods:
– Goldeneye ducks (Bucephala clangula)
– Identified eggs in nests to a specific female in the
population using egg protein polymorphisms
– Monitored nests to determine egg laying
– Quantified the number of eggs or young produced
by each female and her reproductive strategy
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
Featured Research
Conspecific brood parasitism in
ducks
• Results:
– Nesting parasites (who laid
eggs in their own and
another female’s nest) had
the highest reproductive
success
• Conclusion:
– Brood parasitism can
enhance fitness in part by
reducing the cost of parental
care
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press