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Chapter 18Chapter 18 22
Mating Systems & Parental Mating Systems & Parental Care Chapter 18Care Chapter 18
Mating SystemsMating Systems Parental CareParental Care
Who Invests in Offspring?Who Invests in Offspring? Parent-Offspring RecognitionParent-Offspring Recognition
Not covered in lectureNot covered in lecture Parent-Offspring ConflictParent-Offspring Conflict Sibling rivalrySibling rivalry
Chapter 18Chapter 18 33
Factors Affecting Type of Factors Affecting Type of Mating SystemMating System
Sexual SelectionSexual Selection Differential allocation of resources Differential allocation of resources
into gamete production and into gamete production and parental careparental care
Sperm is cheap, eggs expensiveSperm is cheap, eggs expensive
Chapter 18Chapter 18 44
Female Male Limits to
Reproductive Success
# of eggs produced
# of matings
1. Males should be competitive among 1. Males should be competitive among themselves for opportunities to mate themselves for opportunities to mate (Intrasexual competition)(Intrasexual competition)
2. Females should be choosy: any mating 2. Females should be choosy: any mating may involve a big investment on her part, so may involve a big investment on her part, so she should be selective about it (Intersexual she should be selective about it (Intersexual competition)competition)
Factors Affecting Type of Factors Affecting Type of Mating SystemMating System
Chapter 18Chapter 18 55
Sexual selection underlies the evolution of Sexual selection underlies the evolution of male competition and female choice.male competition and female choice.
Type of Mating System dependent on:Type of Mating System dependent on:Amount of parental care requiredAmount of parental care requiredEcological factorsEcological factors
Chapter 18Chapter 18 66
Mating SystemsMating Systems
Most classifications of mating Most classifications of mating systems based on extent of systems based on extent of bonding/association between male bonding/association between male and female during mating.and female during mating.
Problem: Problem: judgment is needed to determined what judgment is needed to determined what
constitutes an associationconstitutes an association SubjectiveSubjective
Emlen & Oring (1977)Emlen & Oring (1977)
Chapter 18Chapter 18 77
Mating SystemsMating Systems
Emlen & Oring (1977):Emlen & Oring (1977): Classification based on Classification based on ability of one ability of one
sex to monopolize or accumulate sex to monopolize or accumulate matesmates Eliminates need for subjective judgmentEliminates need for subjective judgment Emphasizes the Emphasizes the ecological and ecological and
behavioural potential for monopolizationbehavioural potential for monopolization
Chapter 18Chapter 18 88
Emlen and Oring (1977) Emlen and Oring (1977) • the ecology of an organism may not permit the ecology of an organism may not permit males to have more than one partner.males to have more than one partner.•Females widely distributed and males cannot Females widely distributed and males cannot monopolize them. monopolize them. •Females may mate with another male so Females may mate with another male so monogamy may serve to guard the female. monogamy may serve to guard the female. •If males help rear young, fitness increases If males help rear young, fitness increases through increased young survival.through increased young survival.•The evolution mating systems is driven by the The evolution mating systems is driven by the distribution of resources in the environment for distribution of resources in the environment for both the male and the female.both the male and the female.
Resource-based Mating SystemsResource-based Mating Systems
Chapter 18Chapter 18 99
Monogamy - 1 male, 1 femaleMonogamy - 1 male, 1 femalemate guardingmate guardingmate assistancemate assistancefemale enforcedfemale enforced
Polygyny - 1 male, many Polygyny - 1 male, many femalesfemales
resource defenseresource defensefemale defensefemale defensescramble competitionscramble competitionexplosive breeding explosive breeding
assemblageassemblageleklek
Polyandry - 1 female, many Polyandry - 1 female, many malesmales
male defensemale defenseresource defenseresource defense
PromiscuityPromiscuity
Mating SystemsMating Systems
Chapter 18Chapter 18 1010
Mating SystemsMating Systems
Males can produce lots of sperm almost Males can produce lots of sperm almost continuouslycontinuously
Monogamy is not best for a maleMonogamy is not best for a male Females often need help in raising Females often need help in raising
offspring, so monogamy is good for heroffspring, so monogamy is good for her Sexual selection theory and coupled with Sexual selection theory and coupled with
low parental investment of males suggest low parental investment of males suggest that polygynous mating systems should be that polygynous mating systems should be most common. most common.
Why are males?Why are males?
Chapter 18Chapter 18 1111
Mating SystemsMating Systems
MonogamyMonogamy (Association of) 1 male & 1 female(Association of) 1 male & 1 female Neither sex is able to monopolize Neither sex is able to monopolize
more than one member of the more than one member of the opposite sexopposite sex
Mate for season only, or for lifeMate for season only, or for life Genetic constraints vs. social/ Genetic constraints vs. social/
environmental factors (e.g., seabirds environmental factors (e.g., seabirds socially monogamous)socially monogamous)
Chapter 18Chapter 18 1212
Mating SystemsMating Systems
PolygamyPolygamy Matings with multiple partners; non-Matings with multiple partners; non-
monogamous systemsmonogamous systems PolygynyPolygyny: “many” females: “many” females Males able to monopolize >1 femaleMales able to monopolize >1 female PolyandryPolyandry: “many” males: “many” males Females able to monopolize >1 maleFemales able to monopolize >1 male
Chapter 18Chapter 18 1313
Mating SystemsMating Systems
PromiscuityPromiscuity Multiple matings by at least one Multiple matings by at least one
sexessexes Absence of prolonged associationsAbsence of prolonged associations
Chapter 18Chapter 18 1414
Fig. 18.1
Spatial distribution of Spatial distribution of resources influences type of resources influences type of
mating systemmating system
Dots = resources, circles = defended areas
Chapter 18Chapter 18 1515
Polygamy - Types of Polygamy - Types of Polygyny:Polygyny:
Resource-defence polygyny:Resource-defence polygyny: Males defend areas containing food Males defend areas containing food
or nesting sites that females need or nesting sites that females need for reproductionfor reproduction Territories differ quality (clumped Territories differ quality (clumped
distribution)distribution) May reach a point where a female can May reach a point where a female can
do better by mating with an already-do better by mating with an already-mated male on a good territory than mated male on a good territory than an unmated male on a poor territory = an unmated male on a poor territory = polygyny thresholdpolygyny threshold
Chapter 18Chapter 18 1616
Fig. 18-3
The quality of territory at (b) is greater than at (a). A female joining an already-mated male at (b) will have the same RS (c) as a female in a monogamous pair at (a).
Polygyny Polygyny ThresholdThreshold
(a) (b)
Chapter 18Chapter 18 1717
Polygamy – Types of Polygamy – Types of PolygynyPolygyny
Resource-defence polygyny (cont’d):Resource-defence polygyny (cont’d): Facultative (optional) polygyny Facultative (optional) polygyny :: Dependent on locale (clumped, Dependent on locale (clumped,
defensible resources: defensible resources: polygynypolygyny; vs. ; vs. spread-out, non-defensible: spread-out, non-defensible: monogamymonogamy))
Thus, same species may behave Thus, same species may behave differently in different environmentsdifferently in different environments
Chapter 18Chapter 18 1818
Polygamy – Types of Polygamy – Types of PolygynyPolygyny
Female-defence polygyny:Female-defence polygyny: Females aggregate for reasons Females aggregate for reasons
unrelated to matingunrelated to mating E.g., female elephant seals haul out E.g., female elephant seals haul out
onto land to give birth, sites limitedonto land to give birth, sites limited
– Males compete to monopolize the grouped females, defend harem from other males
Chapter 18Chapter 18 1919
Male dominance polygynyMale dominance polygyny Neither resources nor females can Neither resources nor females can
be monopolizedbe monopolized Males gather and display, females Males gather and display, females
choose based on quality of displaychoose based on quality of display Usually on Usually on leksleks (mating areas where (mating areas where
males congregate and defend small males congregate and defend small territories while displaying for territories while displaying for females)females)
E.g., bowerbirds; sage grouseE.g., bowerbirds; sage grouse
Polygamy – Types of Polygamy – Types of PolygynyPolygyny
Chapter 18Chapter 18 2020
Male dominance polygyny (cont’d)Male dominance polygyny (cont’d) Mating success skewed in favour of a Mating success skewed in favour of a
small number of malessmall number of males Dominant males may have:Dominant males may have:
Preferred territory locations within lekPreferred territory locations within lek Most attractive display (e.g., bower)Most attractive display (e.g., bower) Most elaborate ornaments, etc.Most elaborate ornaments, etc.
““Copying” behaviour seen in femalesCopying” behaviour seen in females
Polygamy – Types of Polygamy – Types of PolygynyPolygyny
Chapter 18Chapter 18 2121
Polygamy – Types of Polygamy – Types of PolygynyPolygyny
Scramble PolygynyScramble Polygyny Males actively search for mates Males actively search for mates
without overt competitionwithout overt competition Large groups of females congregate, Large groups of females congregate,
males concentrate only on inseminating males concentrate only on inseminating females or fertilizing eggs, ignore other females or fertilizing eggs, ignore other males (e.g., wood frogs, horseshoe males (e.g., wood frogs, horseshoe crabs); ORcrabs); OR
Widely disbursed females are actively Widely disbursed females are actively pursued by males (e.g., thirteen-lined pursued by males (e.g., thirteen-lined ground squirrels)ground squirrels)
Chapter 18Chapter 18 2222
Polygamy – Types of Polygamy – Types of PolyandryPolyandry
Resource-defence polyandryResource-defence polyandry Females control access to males Females control access to males
indirectly by monopolizing critical indirectly by monopolizing critical resources resources
e.g., spotted sandpiper – females e.g., spotted sandpiper – females compete for control of breeding compete for control of breeding territoriesterritories
Chapter 18Chapter 18 2323
Polygamy – Types of Polygamy – Types of PolyandryPolyandry
Female-access polyandryFemale-access polyandry Females do not defend resources Females do not defend resources
essential to males, but they interact essential to males, but they interact among themselves to limit access to among themselves to limit access to males males e.g., American jacanas – some e.g., American jacanas – some
females defend “superterritories” females defend “superterritories”
which encompass the territories which encompass the territories
of several males, prevent access of several males, prevent access
to other femalesto other females
Chapter 18Chapter 18 2424
PolyandryPolyandry Rare – Rare – Females more brightly Females more brightly
coloured, etc. (sexually-coloured, etc. (sexually-selected traits)selected traits)
Females show Females show philopatryphilopatry: : (returning to (returning to natal territory after natal territory after maturity)maturity)
True of males in True of males in polygynous speciespolygynous species
Chapter 18Chapter 18 2525
Ecology & Mating SystemsEcology & Mating Systems
Mating systems related to resource Mating systems related to resource distributiondistribution
Two sympatric (i.e., coexist in same Two sympatric (i.e., coexist in same area) species of area) species of Agelaius Agelaius (Orians, 1961) (Orians, 1961)
Tricoloured blackbirdsTricoloured blackbirdsRed-winged blackbirdsRed-winged blackbirds
Chapter 18Chapter 18 2626
Ecology & Mating SystemsEcology & Mating Systems
Red-winged Black Birds: Red-winged Black Birds: Usually polygynousUsually polygynous Male defend territory with 2 or 3 femalesMale defend territory with 2 or 3 females Male arrives 3-4 wk before females (often Male arrives 3-4 wk before females (often
natal territory), defends territory until natal territory), defends territory until young are fledged (several months)young are fledged (several months)
Rarely help raise young – females build Rarely help raise young – females build nests and incubatenests and incubate
Chapter 18Chapter 18 2727
Ecology & Mating SystemsEcology & Mating Systems
Tricoloured Black Birds: Tricoloured Black Birds: MonogamousMonogamous Nomadic colonies of 100-200,000 birdsNomadic colonies of 100-200,000 birds Establish territories, find mates, build nests, lay Establish territories, find mates, build nests, lay
eggs (biparental care) – ALL WITHIN 1 WEEK!eggs (biparental care) – ALL WITHIN 1 WEEK! Both sexes make large investment, but in a Both sexes make large investment, but in a
smaller timeframesmaller timeframe
Chapter 18Chapter 18 2828
Ecology & Mating SystemsEcology & Mating Systems
Why so different? Why so different? Depends on Energy source (food Depends on Energy source (food
availability)availability) RWBB: Stable diet of seeds and insects, RWBB: Stable diet of seeds and insects,
available for several monthsavailable for several months TCBB: Mass feeding flights, attack TCBB: Mass feeding flights, attack
ephemeral, concentrated food sources, ephemeral, concentrated food sources, e.g., ripe rice/grain fields e.g., ripe rice/grain fields
Chapter 18Chapter 18 2929Gibbs, et al. 1990. Realized reproductive success of polygynous Red-winged Blackbirds revealed by DNA markers. Science 250: 1394-1397.
Mouse MHC Probe
Chapter 18Chapter 18 3030
Alternative Mating TacticsAlternative Mating Tactics
Members of same sex can use different Members of same sex can use different tactics to obtain matingstactics to obtain matings E.g., some males fight, others sneak E.g., some males fight, others sneak
copulations by being inconspicuous or copulations by being inconspicuous or mimicking femalesmimicking females
““Sneaky”, satellite, or parasitic malesSneaky”, satellite, or parasitic males E.g., bullfrogs: Dominant male calls to E.g., bullfrogs: Dominant male calls to
attract females to his territory; satellite male attract females to his territory; satellite male hides at edge, waits for females to approachhides at edge, waits for females to approach
Chapter 18Chapter 18 3131
Explosive Breeding Explosive Breeding AssemblageAssemblage
•Females become receptive for only a Females become receptive for only a brief timebrief time•They go to a breeding area when they They go to a breeding area when they are readyare ready•Males gather at the breeding location Males gather at the breeding location and compete for the female.and compete for the female.
Chapter 18Chapter 18 3232
Alternative TacticsAlternative Tactics MorphologyMorphology
coho salmon: jacks coho salmon: jacks vs. hooknosesvs. hooknoses
Hooknoses:Hooknoses: built to built to fightfight
Jacks:Jacks: smaller, smaller, mimic females, mimic females, sneak fertilizationssneak fertilizations
(Fig. 18.8)
Chapter 18Chapter 18 3333
Parental CareParental Care Extent of parental care varies greatly across Extent of parental care varies greatly across
speciesspecies Ways to invest:Ways to invest:
DNADNA (release sperm/eggs, move on) (release sperm/eggs, move on) Prenuptial feedingPrenuptial feeding (e.g., crickets) – (e.g., crickets) –
spermatophore spermatophore nourishes female, more nourishes female, more and better quality offspringand better quality offspring
Direct care of offspringDirect care of offspring (incubating, (incubating, feeding, brooding) – birds/mammals/some feeding, brooding) – birds/mammals/some fish…fish…
Chapter 18Chapter 18 3535
Which Sex Invests?Which Sex Invests? Taxonomic differences also exist in patterns Taxonomic differences also exist in patterns
of parental investment:of parental investment: birds:birds: monogamy / biparental care monogamy / biparental care mammals:mammals: polygyny / maternal care polygyny / maternal care fish:fish: promiscuity/polygyny / no parental care or promiscuity/polygyny / no parental care or
male caremale care Why these differences?Why these differences?
Photo by: Alan and Sandy Carey
Chapter 18Chapter 18 3636
Determinants of Parental Determinants of Parental Investment in VertebratesInvestment in Vertebrates
Mode of fertilizationMode of fertilization Internal fertilization – primarily Internal fertilization – primarily
female care female care E.g., birds, mammalsE.g., birds, mammals
External fertilization –External fertilization – primarily primarily biparental or male care biparental or male care E.g., fishE.g., fish
Chapter 18Chapter 18 3737
Determinants of Parental Determinants of Parental Investment in VertebratesInvestment in Vertebrates
Certainty of Paternity HypothesisCertainty of Paternity Hypothesis Reliability of paternity assumed to be Reliability of paternity assumed to be
greater when eggs are fertilized greater when eggs are fertilized externally (e.g., fish) rather than externally (e.g., fish) rather than internally (e.g., mammals, birds)internally (e.g., mammals, birds)
Chapter 18Chapter 18 3838
Determinants of Parental Determinants of Parental Investment in VertebratesInvestment in Vertebrates
Association HypothesisAssociation Hypothesis Proximity of adults to offspringProximity of adults to offspring Internal fertilization – females closerInternal fertilization – females closer External fertilization – both sexes close, but External fertilization – both sexes close, but
male/biparental care more common when male/biparental care more common when offspring associated with a male’s territoryoffspring associated with a male’s territory
E.g., males defend territories, little extra E.g., males defend territories, little extra energy to protect eggs already on territory energy to protect eggs already on territory (e.g., fish)(e.g., fish)
Chapter 18Chapter 18 3939
Determinants of Parental Determinants of Parental Investment in VertebratesInvestment in VertebratesPhylogenetic Constraints:Phylogenetic Constraints:
BirdsBirds Eggs develop externallyEggs develop externally Incubation, feeding, guarding by Incubation, feeding, guarding by
both sexesboth sexes
Mammals Mammals Internal gestationInternal gestation LactationLactation Males can provide little Males can provide little carecare
Chapter 18Chapter 18 4040
Determinants of Parental Determinants of Parental Investment in VertebratesInvestment in Vertebrates
Phylogenetic Phylogenetic constraintsconstraints
FishFish External fertilizationExternal fertilization Both sexes free to Both sexes free to
desert, ordesert, or Guard nest site Guard nest site
(territory)(territory)
Chapter 18Chapter 18 4141
Determinants of Determinants of Parental Investment in Parental Investment in VertebratesVertebrates
Reproductive Effort:Reproductive Effort: Total energy Total energy expended in reproducing, which expended in reproducing, which includes includes mating effort & parental caremating effort & parental care
May direct all reproductive effort into May direct all reproductive effort into mating (e.g., codfish - lay eggs, mating (e.g., codfish - lay eggs, fertilize them, swim away), ORfertilize them, swim away), OR
May expend much energy in parental May expend much energy in parental care (e.g., primates – 25% of care (e.g., primates – 25% of offspring’s lifespan)offspring’s lifespan)
Chapter 18Chapter 18 4242
Reproductive EffortReproductive Effort
Male
MALE
Female
FEMALE
ME
PE
PE MEPE
PE
PE
PE
ME
PE
PE
ME
Mating Mating SystemSystem
Polygamous/Polygamous/PromiscuousPromiscuous MonogamousMonogamous
Chapter 18Chapter 18 4343
Determinants of Parental Determinants of Parental Investment in VertebratesInvestment in Vertebrates
How Do Ecological Factors Affect How Do Ecological Factors Affect Parental Investment?Parental Investment? K- & r-selection theoryK- & r-selection theory ““Bet-hedging” theoryBet-hedging” theory
Chapter 18Chapter 18 4444
r - & K- Selection Theoryr - & K- Selection Theory
Stable environmentStable environment Larger body sizeLarger body size Slower developmentSlower development Longer lifespanLonger lifespan Have young at Have young at
intervals (intervals (iteroparityiteroparity);); K-selectedK-selected (at/near (at/near
carrying capacity of carrying capacity of environment, K)environment, K)
few young that receive few young that receive much care much care
Fluctuating Fluctuating environmentenvironment Small body sizeSmall body size Rapid developmentRapid development Have young all at once Have young all at once
((semelparitysemelparity),), r-selectedr-selected (at/near (at/near
reproductive rate of reproductive rate of population, r)population, r)
many young that receive many young that receive little/no care little/no care
Chapter 18Chapter 18 4545
““Bet-hedging” TheoryBet-hedging” Theory
In environments where survival of offspring In environments where survival of offspring is low and unpredictable, parents may is low and unpredictable, parents may “hedge their bets” by putting in only a small “hedge their bets” by putting in only a small reproductive effort each seasonreproductive effort each season spread their reproductive effort out over time spread their reproductive effort out over time
rather than all at oncerather than all at once e.g., California Gull: Lives 15+ yrs. As adults e.g., California Gull: Lives 15+ yrs. As adults age, appear to increase effort (lay more eggs, age, appear to increase effort (lay more eggs, feed chicks more food, defend more vigorously) feed chicks more food, defend more vigorously) due to their own decreasing reproductive due to their own decreasing reproductive potential.potential.
Chapter 18Chapter 18 4646
Parent-Offspring Parent-Offspring RecognitionRecognition
Misdirected parental care can be Misdirected parental care can be costly (waste of energy, reduced costly (waste of energy, reduced fitness)fitness) Fostering in sealsFostering in seals
Recognition appears to evolve in Recognition appears to evolve in species in which mixing of species in which mixing of unrelated offspring is likelyunrelated offspring is likely
Chapter 18Chapter 18 4747
colonial ground-nesting gulls & terns:colonial ground-nesting gulls & terns: precocial chicks mobile at ~5 days,precocial chicks mobile at ~5 days, adults seem to develop recognition for adults seem to develop recognition for
own chicks at that timeown chicks at that time kittiwakeskittiwakes
cliff-nesters;cliff-nesters; chicks fledge at 3 weeks chicks fledge at 3 weeks Parents do not seem to recognize Parents do not seem to recognize
offspringoffspring
Chapter 18Chapter 18 4848
Parent-Offspring ConflictParent-Offspring Conflict
Offspring demand more investment Offspring demand more investment from the parent (usually mother) than from the parent (usually mother) than the parent is willing to givethe parent is willing to give
Trivers (1974):Trivers (1974): Natural selection acts Natural selection acts differently on mother and offspringdifferently on mother and offspring Based on coefficient of relatedness and Based on coefficient of relatedness and
parental investmentparental investment
Chapter 18Chapter 18 4949
Parent-Offspring ConflictParent-Offspring Conflict MotherMother - should invest a certain amount of - should invest a certain amount of
energy into first offspring, “wean” him, then energy into first offspring, “wean” him, then invest in producing second offspring, when the invest in producing second offspring, when the cost of raising #1 starts to exceed the benefits cost of raising #1 starts to exceed the benefits of having #2…of having #2…
OffspringOffspring - should “demand” investment from - should “demand” investment from mother until such point that the mother’s mother until such point that the mother’s fitness starts to decline (&, thus, so does his fitness starts to decline (&, thus, so does his inclusive fitness, as he shares half his genes inclusive fitness, as he shares half his genes with her).with her).
when cost of raising #1 becomes 2x the when cost of raising #1 becomes 2x the benefit to mother, offspring's inclusive fitness benefit to mother, offspring's inclusive fitness
Chapter 18Chapter 18 5050
Parental Reproductive Parental Reproductive SuccessSuccess
How can parents increase their How can parents increase their reproductive success and fitness?reproductive success and fitness?
Manipulation of dependent youngManipulation of dependent young
Chapter 18Chapter 18 5151
Parental ManipulationParental Manipulation
Parents may selectively provide care Parents may selectively provide care to certain offspring at the expense of to certain offspring at the expense of others others
Brood adjustmentBrood adjustment Coots - selectively adjusts brood size by Coots - selectively adjusts brood size by
killing chicks (European) or feeding killing chicks (European) or feeding specific chicks (American) specific chicks (American)
Chapter 18Chapter 18 5252
Parental ManipulationParental Manipulation
Hatching asynchronyHatching asynchrony - milder form of - milder form of brood adjustment: first-to-hatch have brood adjustment: first-to-hatch have advantage, get more food, larger, can advantage, get more food, larger, can push others out of nest (i.e., siblicide)push others out of nest (i.e., siblicide)
It is in parents’ interests to create It is in parents’ interests to create inequalities in size of chicks: WHY?inequalities in size of chicks: WHY? biggest, strongest offspring survive and biggest, strongest offspring survive and
are more likely to reach reproductive are more likely to reach reproductive ageage
Chapter 18Chapter 18 5353
Sibling RivalrySibling Rivalry
young predatory birds (ex: boobies, young predatory birds (ex: boobies, eagles, egrets) kill younger siblings eagles, egrets) kill younger siblings soon after hatching, soon after hatching,
may be because the second egg serves may be because the second egg serves only as parental insurance in case the only as parental insurance in case the first fails to hatch. first fails to hatch.
Pigs: “runt” gets least preferred teat (little Pigs: “runt” gets least preferred teat (little milk); piglets have sharp teeth and fight for milk); piglets have sharp teeth and fight for access to best nipplesaccess to best nipples