Mating Systems & Parental Care. Chapter 182 Mating Systems & Parental Care Chapter 18 Mating Systems Mating Systems Parental Care Parental Care Who Invests.

Mating SystemsMating Systems

&&

Parental CareParental Care

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


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


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


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



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)



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


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


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




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?



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)



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



PromiscuityPromiscuity Multiple matings by at least one Multiple matings by at least one

sexessexes Absence of prolonged associationsAbsence of prolonged associations


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


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


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)


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



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


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



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




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)


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


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


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


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



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



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



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


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


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.


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)


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…


See Text pg. 151 (Chapter 10)See Text pg. 151 (Chapter 10)


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


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



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)



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)


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



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)


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)


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



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


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


““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.


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


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


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


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


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


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)


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


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


Case Study: Spotted hyenasCase Study: Spotted hyenas

Mating Systems & Parental Care. Chapter 182 Mating Systems & Parental Care Chapter 18 Mating Systems Mating Systems Parental Care Parental Care Who Invests.

Documents

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