Chapter 12
Chapter 12 •
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Parental care balance – predators can ambush parent or nest o Sea turtles: hatch in sand, off to sea on own o Differ on duration, amount, timing, and who o Tree hoppers –guards eggs and repel predators o Egrets: brood young until independence (fledging) o Primates: feed and protect young until independence Classical view – parents unselfish provider, child recipient Evolutionary: benefits – increased offspring survival, cost of future reproduction o Trade off of current and future production o Birds with low adult mortality – minimize self risk , high mortality rate – more sensitive to nest Why care? Physiological costs – sustained energy cost o Future reproduction and survival o Opportunity costs – foraging and matings Parental care evolves if there is a net fitness increase
Factors which affect cost and benefit of environment • Environmental o K selected: stable environment, large body size, slower development, longer lifespan. (quality) intraspecific competition Iteroparity: offspring in successive bouts Small # of young that receive care Low mortality of young Parental strategy: Intelligent, autonomous – expensive offspring • Learning and physical abilities – benefit of parental investment – increase in success of young Altrical young: relatively helpless and immature Example: monkeys – flexible behaviour, behaiour repertoire, social system, develop brain • African dogs – social system, group hunting o R selected: fluctuating environment, smaller body size, rapid development, shorter lifespan (quantity) Environmental, fluctuation, predation selecton factor Semelparity: production of offspring once/few in a lifetime Large # of young that receive little to no care High mortality rate of young Parental strategy: large # of cheap offspring – some survive • Low benefit of parental involvement Prococial young: relatively advanced stage Example: Coho salmon: ocean environment, single explosive breeding event, parents die and no care
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Clutchlings may die 100% to predation, water problems Redback spiders: disperse as spiderlings to unpredictable habitats – thousands of offspring for a mother – tiny and no parental care – high mortality rates, catch prey autonomous Gross simplication, biotic and abiotic factors affect selection on favoured traits of offspring, and some require care to develop o Gull – start off K selected, as parents age become R selected o Likelihood of survival at old age decreases, so does parental investment Residual reproductive value o Function of age and expected reproductive lifespan opportunities How many surviving offspring are you likely to have o Lower RRV = lower cost of parental investment Factors affecting RRV = age, health, timing, finding future mates Eg. Eresid spiders o 100 of offspring and high offspring mortality – r selected o spider adult longevity – 1 summer – low RRV o suicidal maternal care – offspring feed on mother – low RRV
Who provides Care • •
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exclusive mom/dad, male or female, biparent Female biased parental care o Females invested so much energy in making eggs – incentive to make sure gametic investment is not wasted However, idea fails when we observe female leaving eggs Concorde Fallacy (sunk costs) o Larger benefit-cost difference A) lower cost: opportunity for additional mating • Cost Male > female, so female care o B) highest benefit: Females always derive max since offspring are hers Sperm competition • Benefit female > male, so female care More common in external than internal fertilization • Male can see which eggs are fertilized that are his Mouth broodingfish (St Peter) o Gamete production constrains female but not male reproduction But caring males fertilize same # of eggs o Females take longer to spawn than males Both lose weight from caring • Overall more costly for females Exceptions to the rule o Male sticklebacks can care for more eggs clutches
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o Female can forage more freely – more growth – more eggs Why unilateral care female – increased cost for male leads to desertion
How much care • Eventually parents benefit more by abandoning young o Increasing cost and diminishing retuns • Offspring want maximum investment but there are fitness benefits of deferring to siblings and relatives • parent/offspring conflict – balance cost to future offspring o avoid additional investment if it cost more to future offspring than current offspring • Offspring balance benefit against half the cost to new offspring o Depends on relatedness o Conflict = genetic selfishness of parent o Parent related to all offspring (r = 0.5) so share care o Offspring related to itself (1) and 0.5 to offspring seeks more care • Sibling rivalry - siblicide o Infants want to aquire as much resource as possible until indirect fitness outweight direct benefits – increase in Inclusive fitness • Peaceful parenting – parent/offspring conflict – peaceful separation o Example in humans – fetus preeclampsia to acquire max resources • Siblicide o Resource competition o Food in small units o Spatial confinement o Weaponry o Competitive disaparities • Overproduction of eggs by parents set the stage for siblicide – parental complicity • Why extra eggs o Insurance egg hypothesis – insurance against clutch failure Obligate siblicide (if all chicks survive, inferior is killed) – fixed number of core offspring High risk of nest failure Parental complicity Unrelated to food limitation o Extra reproductive hypothesis – lay extra egg to account for environmental randomness Facultative siblicide – only occurs if lack food Variable resources and nest success Parental complicity Food limitation o Both ideas have parental complicity – kill weak with min cost • Parental complicity – ensure ease of killing weaker o Asynchronous breeding – eggs over several days
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Hatches at different time, A > B > C size o In non siblicidal species, brood is delayed so hatching is same Prediction: natural asynchrony = higher nesting survival o Synchronized vs. control vs. 2x hatching interval o Normal most survival o Synchronized more fighting, less survival o Double: more fighting even if sufficient food Differential hormonal provisioning of eggs o Testosterone increase competitiveness and aggression of juvenile chicks 1>2>3 (non siblicidal asynchronous, testosterone is reversed – canaries) as food is limited, aggression to junior chicks increase, and parents feed elder Obligate – high loss of a chick (insurance of extra young) Facultative- rearing of B chicks under high food (extra value of extra young) Sibling rivalry may be important o Blue footed booby prevent killing of junior o Cattle egret: dominant kills junior o Facultative siblicide increases parental fitness, fewer competition
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Water bug do all the work o Panda principle – can only grow as big as early size In order to be large at first, they need oxygen = brooding o Males can clutch more eggs, and so multiple females will join him Females need to go seek prey to have more eggs
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Discriminating parental care o Some bats can discriminate and nurse their own young o Make signals and calls
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Why adopt genetic strangers o Experiments of attack because transferred chicks were scared Voluntary leaving = do not flee o Rule of thumb – adoption is rare
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Brood paratism o Fight for territory – brood both o Territorial female can boost fitness by enlisting parental care o Gradual shift hypothesis: brood parasites should find species closely related to them o Some brood parasites take advantage of unrelated species smaller than them – sensory exploitation Great tit thrive in blue tit, but not vice versa Why accept brood parasites
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o If parasites only victimize a small proportion, the risk of recognition error is greater than just accepting the egg o Some species cannot remove the eggs Abandon clutch – leave or build a nest on top of old Stay and brood all eggs Cost-benefit analysis o Mafia hypothesis: if risk of error is low, parasite can just go back and destroy eggs of the young if own egg was destroyed Punish host who destroyed parasitic egg o Evolutions arm race: one party is not evolved yet to identify Chicks can even micmic feeding call Parental Favoritism • How to invest into progeny o Different allocation of food and resources Evaluate Reproductive Value of Offspring •
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Well fed youngsters pay back o Judge juveniles by begging and appearance o Redder mouths of birds – more carteonids – strong immune function Might just be the colour Reproductive value: youngs who have a highly likelihood to fledge and reproduce
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Parental care balance – predators can ambush parent or nest o Sea turtles: hatch in sand, off to sea on own o Differ on duration, amount, timing, and who o Tree hoppers –guards eggs and repel predators o Egrets: brood young until independence (fledging) o Primates: feed and protect young until independence Classical view – parents unselfish provider, child recipient Evolutionary: benefits – increased offspring survival, cost of future reproduction o Trade off of current and future production o Birds with low adult mortality – minimize self risk , high mortality rate – more sensitive to nest Why care? Physiological costs – sustained energy cost o Future reproduction and survival o Opportunity costs – foraging and matings Parental care evolves if there is a net fitness increase
Factors which affect cost and benefit of environment • Environmental o K selected: stable environment, large body size, slower development, longer lifespan. (quality) intraspecific competition Iteroparity: offspring in successive bouts Small # of young that receive care Low mortality of young Parental strategy: Intelligent, autonomous – expensive offspring • Learning and physical abilities – benefit of parental investment – increase in success of young Altrical young: relatively helpless and immature Example: monkeys – flexible behaviour, behaiour repertoire, social system, develop brain • African dogs – social system, group hunting o R selected: fluctuating environment, smaller body size, rapid development, shorter lifespan (quantity) Environmental, fluctuation, predation selecton factor Semelparity: production of offspring once/few in a lifetime Large # of young that receive little to no care High mortality rate of young Parental strategy: large # of cheap offspring – some survive • Low benefit of parental involvement Prococial young: relatively advanced stage Example: Coho salmon: ocean environment, single explosive breeding event, parents die and no care
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• • • •
Clutchlings may die 100% to predation, water problems Redback spiders: disperse as spiderlings to unpredictable habitats – thousands of offspring for a mother – tiny and no parental care – high mortality rates, catch prey autonomous Gross simplication, biotic and abiotic factors affect selection on favoured traits of offspring, and some require care to develop o Gull – start off K selected, as parents age become R selected o Likelihood of survival at old age decreases, so does parental investment Residual reproductive value o Function of age and expected reproductive lifespan opportunities How many surviving offspring are you likely to have o Lower RRV = lower cost of parental investment Factors affecting RRV = age, health, timing, finding future mates Eg. Eresid spiders o 100 of offspring and high offspring mortality – r selected o spider adult longevity – 1 summer – low RRV o suicidal maternal care – offspring feed on mother – low RRV
Who provides Care • •
•
•
exclusive mom/dad, male or female, biparent Female biased parental care o Females invested so much energy in making eggs – incentive to make sure gametic investment is not wasted However, idea fails when we observe female leaving eggs Concorde Fallacy (sunk costs) o Larger benefit-cost difference A) lower cost: opportunity for additional mating • Cost Male > female, so female care o B) highest benefit: Females always derive max since offspring are hers Sperm competition • Benefit female > male, so female care More common in external than internal fertilization • Male can see which eggs are fertilized that are his Mouth broodingfish (St Peter) o Gamete production constrains female but not male reproduction But caring males fertilize same # of eggs o Females take longer to spawn than males Both lose weight from caring • Overall more costly for females Exceptions to the rule o Male sticklebacks can care for more eggs clutches
•
o Female can forage more freely – more growth – more eggs Why unilateral care female – increased cost for male leads to desertion
How much care • Eventually parents benefit more by abandoning young o Increasing cost and diminishing retuns • Offspring want maximum investment but there are fitness benefits of deferring to siblings and relatives • parent/offspring conflict – balance cost to future offspring o avoid additional investment if it cost more to future offspring than current offspring • Offspring balance benefit against half the cost to new offspring o Depends on relatedness o Conflict = genetic selfishness of parent o Parent related to all offspring (r = 0.5) so share care o Offspring related to itself (1) and 0.5 to offspring seeks more care • Sibling rivalry - siblicide o Infants want to aquire as much resource as possible until indirect fitness outweight direct benefits – increase in Inclusive fitness • Peaceful parenting – parent/offspring conflict – peaceful separation o Example in humans – fetus preeclampsia to acquire max resources • Siblicide o Resource competition o Food in small units o Spatial confinement o Weaponry o Competitive disaparities • Overproduction of eggs by parents set the stage for siblicide – parental complicity • Why extra eggs o Insurance egg hypothesis – insurance against clutch failure Obligate siblicide (if all chicks survive, inferior is killed) – fixed number of core offspring High risk of nest failure Parental complicity Unrelated to food limitation o Extra reproductive hypothesis – lay extra egg to account for environmental randomness Facultative siblicide – only occurs if lack food Variable resources and nest success Parental complicity Food limitation o Both ideas have parental complicity – kill weak with min cost • Parental complicity – ensure ease of killing weaker o Asynchronous breeding – eggs over several days
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•
• • • •
Hatches at different time, A > B > C size o In non siblicidal species, brood is delayed so hatching is same Prediction: natural asynchrony = higher nesting survival o Synchronized vs. control vs. 2x hatching interval o Normal most survival o Synchronized more fighting, less survival o Double: more fighting even if sufficient food Differential hormonal provisioning of eggs o Testosterone increase competitiveness and aggression of juvenile chicks 1>2>3 (non siblicidal asynchronous, testosterone is reversed – canaries) as food is limited, aggression to junior chicks increase, and parents feed elder Obligate – high loss of a chick (insurance of extra young) Facultative- rearing of B chicks under high food (extra value of extra young) Sibling rivalry may be important o Blue footed booby prevent killing of junior o Cattle egret: dominant kills junior o Facultative siblicide increases parental fitness, fewer competition
•
Water bug do all the work o Panda principle – can only grow as big as early size In order to be large at first, they need oxygen = brooding o Males can clutch more eggs, and so multiple females will join him Females need to go seek prey to have more eggs
•
Discriminating parental care o Some bats can discriminate and nurse their own young o Make signals and calls
•
Why adopt genetic strangers o Experiments of attack because transferred chicks were scared Voluntary leaving = do not flee o Rule of thumb – adoption is rare
•
Brood paratism o Fight for territory – brood both o Territorial female can boost fitness by enlisting parental care o Gradual shift hypothesis: brood parasites should find species closely related to them o Some brood parasites take advantage of unrelated species smaller than them – sensory exploitation Great tit thrive in blue tit, but not vice versa Why accept brood parasites
•
o If parasites only victimize a small proportion, the risk of recognition error is greater than just accepting the egg o Some species cannot remove the eggs Abandon clutch – leave or build a nest on top of old Stay and brood all eggs Cost-benefit analysis o Mafia hypothesis: if risk of error is low, parasite can just go back and destroy eggs of the young if own egg was destroyed Punish host who destroyed parasitic egg o Evolutions arm race: one party is not evolved yet to identify Chicks can even micmic feeding call Parental Favoritism • How to invest into progeny o Different allocation of food and resources Evaluate Reproductive Value of Offspring •
•
Well fed youngsters pay back o Judge juveniles by begging and appearance o Redder mouths of birds – more carteonids – strong immune function Might just be the colour Reproductive value: youngs who have a highly likelihood to fledge and reproduce
