Mating Systems

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Mating Systems

• Psychology 3107

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Introduction

• For the most part, males involvement in mating,
  well, ends after the mating
• Females pay for the mating a lot more
• Physiologically
• Post birth/hatch care
• Therefore, we should expect Polygyny where males
  have more than one mate
• Male variance gt female variance

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Polygyny

• There are several theories about polygyny
• Resource defense polygyny
• Male defends some good resource
• Example, hummingbirds
• The resource is some nectar giving flower

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Hummingbirds

• Male sets up territory
• Excludes other males
• Basically, the male exchanges letting females
  feed in exchange for copulations
• Sort of like nuptial gifts in some sinsects, but
  the gift is stationary
• Females then set up breeding territory withing
  males teritorry

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Polygyny Threshold

• Polygyny may occur when the polygyny threshold
  is crossed
• Example here is migratory songbirds
• Males arrive, set up territories
• Females choose mates

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Polygyny Threshold

• When differences in qualities of available
  territories crosses the polygyny threshold, then
  polygyny results
• It is more profitable for the female to become a
  secondary female with a high end male, then a
  primary femle with a mid range

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What about monogamy

• Monogamy should happen if
• Curves are far apart
• Curves are flat
• In other words, little variation in quality of
  males and their territories
• Verner and Wilson did a really cool study that
  looked at these ideas

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Verner and Wilson

• Marsh birds
• Quality varies greatly
• vs
• Non Marsh birds
• Not so much variation
• Prediction is that there should be much more
  monogamy in non marsh living songbirds

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So, what happened

• Marsh species ? 44 are polygynous
• Non Marsh ? 2 are polygynous
• You can also get female defense polygyny
• Males basically guard the females
• Good example here is in Bison

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But you said wed talk about monogamy

• OK, OK
• When should mongamy happen?
• When the young are in need of lots of parental
  care
• When Territories or resources are poor
• When females actually enforce it!
• Some monogamous species arent..

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Extra Pair Copulations

• Happens a lot in birds
• Ummm, happens a lot in people
• sperm competition
• Usually when female is unguarded or when male can
  get away with it..
• Sperm Wars

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Polyandry

• One female, many males
• Exceedingly rare
• Usually only happens when there is complete sex
  role reversal
• Sea horses
• Spotted sandpipers

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Conclusions

• Many theories as to why different animals have
  different mating systems
• Polygyny is by far the most common
• When you think about it, the system correlates
  nicely with the gametes!