Animal Behavior Quiz 12

Polygyny

male with multiple mates

Polygynandry

female with multiple mates

What shapes mating systems? (evolutionary forces that mold mating systems)

1) Differential Parental Investment

2) Needs of young and potential help by mate

3) Certainty of paternity

4) Environmental potential for polygamy

Differential parent investment (arising from anisogamy)

• sexual differences parental investment

  • male RS limited by matings

  • female RS limited by resources

• Basic sexual difference leads to a higher potential for males to mate multiply

Needs of young & potential help by male

altricial - highly dependent

precocial - not as dependent

• determines the degree to which males and females can maximize RS

  • either spend a lot on care or on mating

Certainty of paternity

males certain of paternity are more likely to stay to help

External vs internal fertilization

• external : synchronization of egg laying and mating

• internal : separation in time of egg laying and mating

Environmental potential for polygamy

degree to which one sex can monopolize access to the other

Extent of monopolization dependent on social and ecological factors that affect distribution of females

1) Spatial distribution (uniform/clumped) - where located

2) Temporal distribution (asynchronous/synchronous) - when fertile

Height of bars = potential for polygany

x axis : spatial distribution of males

• uniform (evenly spread out)

• totally clumped (all together)

  • when all clumped, can monopolize more females

y axis: temporal availability of mates

• Absolute synchrony : all females receptive at once

• Total asynchrony : females become receptive at diff times

  • if all females synchronous, single male cannot mate with many at once

  • if females asynchronous, one male can mate with multiple females → increase polygany potential

What is the ideal for polygany

moderate asynchronous and clumped

clumped : multiple females in on area 

moderate asynchrony : staggers female receptivity just enough for a single male to mate with several females

efficiently monopolize access to multiple mates in both space and time

Why monogamy?

1) Female Dispersion

2) Mate assistance monogamy

3) Mate guarding monogamy

Female Dispersion

• one of best predictors of monogamy 

• when females live separately and widely dispersed, males cannot dominate or defend more than one

Mate assistance monogamy

if involvement of both parents needed to raise baby → expect monogamy

parental care sometimes essential for offspring survival 

Emperor Penguins

• parents take turns going to sea for fish

Hamsters

• males pull offspring out of birth canal

Example of mate assistance monogamy (Starlings)

parental care sometimes significantly increases offspring survival

• incubating by males keep temp high and stable

• males treated with anti-androgen → provided more food, males treated with T → less food

• Males can increase fitness if stay home to take care of babies

Mate guarding monogamy

prevent female from mating with others

if females are

• receptive after mating

• hard to encounter

males can stick around and mate guard → monogamy

Why is monogamy rare in mammals (<10%)?

Delayed Fertilization

• males have low confidence of paternity

Female biased parental care

• internal gestations

  • only females can care for young during early egg stage

• Female only feeding 

  • care for newborns in a way that males cannot

Some exceptions : males bring food

Why is (social) monogamy common in birds (>90%)

• Delayed Fertilization 

  • males have low confidence of paternity but…

• Both sex parental care

  • external gestation

    • one egg laid, male can care for them as well as female

• Both sexes feed

Why do females engage in multiple matings? (costs)

STDs/ infection 

• primates (41 species)

  • # of males typical of species and correlated w/ white blood cells (measure of immune system readiness)

What benefits counter costs of mating multiply?

1) fertility insurance

2) good genes

3) genetic compatibility

4) infanticide reduction

Fertility insurance

increasing the chance of having all eggs fertilized

EX

increase hatching of eggs in multiply mated - red wing blackbirds

Good genes

• Trading up mating w/ genetically superior males

• assortative parenting - mating w/ similar rank

EX

blue tit females solicit EPCS only from higher quality males

yellow toothed cavy females increase offspring survival when mating multiply

What are male options? why stick around and care for youn that might not be yours

• good for males if they are the one to get EPCS

• can be best of bad situations

Genetic compatibility

Genotype matching

females prefer males w/ dissimilar immune system

in blue throat - nest environment was held constant → extra pair youn stronger immune system than within pair young

Infanticide reduction

confuse males abt paternity, so infanticide less likely

Four types of polygyny

Scramble competition

Female Defense

Resource Defense

Leks

Scramble competition

distributed widely - scramble for access to females

what do females get out of this? 

• males of highest quality most likely to mate 

NO CHOICE

Female defense

males gain access to females directly by keeping rivals away

• huge variation in mating success among males

  • ex) southern elephant seals

Why do females stick together?

• benefits of grouping outweigh breeding solitarily

  • various group benefits (reduce predation, increase foraging success)

Resource Defense

Males gain access to females indirectly by monopolizing access to resources that are valuable to females

ex) 

• water striders

  • floating leaves (oviposition)

• African cichlids

  • guard shells (oviposition)

What do females get out of this

• good territory, food, oviposition, protection

Polygyny threshold model

Is polygyny best for females

ex) pied flycatchers

• females in polygynous relationship often have reduced fitness as result of sharing the male

Why be secondary female when OSR typically male biased?

benefit depend on variation in territory and male quality

Process of polygyny threshold model

• males arrive first and settle

• females arrive sequentially 

  • 1st female goes to best territory

  • 2nd goes to next - best territory

• when does it benefit females to join as seconday females

  • weigh btwn : male’s undivided care

    versus male/territory quality

the point where it pays to go to an already occupied territory = polygyny threshold

its all abt individual decision 

• each female decides what is best for her

• variation in habitat quality leads to polygyny 

Lek polygyny

an area where males that provide no parental care, strut their stuff and attract males but don’t defend any resources (other than display site)

Why are leks rare

• lack of parental care is rare in birds

• resources are usually monopolizable

Question remains: in a system with no direct benefits and widely dispersed females, you usually have scramble competition. Why do leks evolve sometimes?

NO CLEAR ANSWER

Where leks from

1) hotspots - males congregate around areas that females pass through

2) hot shots - males congregate around superior individuals 

Lek paradox: how genetic variation maintained

when selction is very strong only a few individuals will contribute genes to next gen

when most everyone in next gen have same dad, will be genetically similar - so there won’t be much genotypic variation after few gens

what benefit is there to females in exhibiting choice

two ways genetic variation maintained HYP 1

Hypothesis 1: genic capture (polygenic effects -many genes effect a trait)

• sexually selected traits often have differential costs (handicaps) and ability to pay costs depends on overall physiological conditions 

• bc overall condition is influenced by many genes, huge target where genetic variation can arise

wo ways genetic variation maintained HYP 2

Hypothesis 2: Red Queen

• long term environmental (biotic) shifts may favor diff traits over time

what is best now may be difference in future - due to red queen cycling 

leading to constant benefits to rare genotypes