Mating SystemsMating Systems

Psychology 3107Psychology 3107

IntroductionIntroduction

For the most part, males’ involvement in For the most part, males’ involvement in mating, well, ends after the matingmating, well, ends after the mating

Females pay for the mating a lot moreFemales pay for the mating a lot more PhysiologicallyPhysiologically Post birth/hatch carePost birth/hatch care

Therefore, we should expect Polygyny Therefore, we should expect Polygyny where males have more than one matewhere males have more than one mate Male variance > female varianceMale variance > female variance

PolygynyPolygyny

There are several There are several theories about polygynytheories about polygyny

Resource defense Resource defense polygynypolygyny Male defends some Male defends some

good resourcegood resource

Example, hummingbirdsExample, hummingbirds

The resource is some The resource is some nectar giving flowernectar giving flower

HummingbirdsHummingbirds

Male sets up territoryMale sets up territory

Excludes other males Excludes other males

Basically, the male exchanges letting Basically, the male exchanges letting females feed in exchange for copulationsfemales feed in exchange for copulations

Sort of like nuptial gifts in some sinsects, Sort of like nuptial gifts in some sinsects, but the ‘gift’ is stationarybut the ‘gift’ is stationary

Females then set up breeding territory Females then set up breeding territory withing male’s teritorrywithing male’s teritorry

Polygyny ThresholdPolygyny Threshold

Polygyny may occur Polygyny may occur when the ‘polygyny when the ‘polygyny threshold’ is crossedthreshold’ is crossed

Example here is Example here is migratory songbirdsmigratory songbirds Males arrive, set up Males arrive, set up

territoriesterritories Females choose Females choose

matesmates

Polygyny ThresholdPolygyny Threshold

When differences in qualities of available When differences in qualities of available territories crosses the polygyny threshold, territories crosses the polygyny threshold, then polygyny resultsthen polygyny results It is more profitable for the female to become It is more profitable for the female to become

a secondary female with a high end male, a secondary female with a high end male, then a primary femle with a mid rangethen a primary femle with a mid range

What about monogamyWhat about monogamy

Monogamy should happen if:Monogamy should happen if: Curves are far apartCurves are far apart Curves are flatCurves are flat

In other words, little variation in quality of males In other words, little variation in quality of males and their territoriesand their territories

Verner and Wilson did a really cool study Verner and Wilson did a really cool study that looked at these ideasthat looked at these ideas

Verner and WilsonVerner and Wilson

Marsh birdsMarsh birds Quality varies greatlyQuality varies greatly

vsvs

Non Marsh birdsNon Marsh birds Not so much variationNot so much variation

Prediction is that there should be much Prediction is that there should be much more monogamy in non marsh living more monogamy in non marsh living songbirdssongbirds

So, what happenedSo, what happened

Marsh species Marsh species 44 % are polygynous 44 % are polygynous

Non Marsh Non Marsh 2 % are polygynous 2 % are polygynous

You can also get female defense polygynyYou can also get female defense polygyny Males basically guard the femalesMales basically guard the females Good example here is in BisonGood example here is in Bison

But you said we’d talk about But you said we’d talk about monogamy…monogamy…

OK, OK……OK, OK……

When should mongamy happen?When should mongamy happen? When the young are in need of lots of When the young are in need of lots of

parental careparental care When Territories or resources are poorWhen Territories or resources are poor When females actually enforce it!When females actually enforce it!

Some ‘monogamous’ species aren’t…..Some ‘monogamous’ species aren’t…..

Extra Pair CopulationsExtra Pair Copulations

Happens a lot in birdsHappens a lot in birds

Ummm, happens a lot Ummm, happens a lot in peoplein people

‘‘sperm competition’sperm competition’ Usually when female is Usually when female is

unguarded or when unguarded or when male can get away male can get away with it…..with it…..

Sperm WarsSperm Wars

PolyandryPolyandry

One female, many One female, many malesmales

Exceedingly rareExceedingly rare

Usually only happens Usually only happens when there is when there is complete sex role complete sex role reversalreversal Sea horsesSea horses Spotted sandpipersSpotted sandpipers

ConclusionsConclusions

Many theories as to why different animals Many theories as to why different animals have different mating systemshave different mating systems

Polygyny is by far the most commonPolygyny is by far the most common

When you think about it, the system When you think about it, the system correlates nicely with the gametes!correlates nicely with the gametes!