Mating Systems

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Mating Systems

• Males can produce lots of sperm almost
  continuously
• Why would a male want only one female?
• Monogamy is not best for a male
• Females often need help in raising offspring, so
  monogamy is good for her

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Conditions Favoring Monogamy

• Mate Assistance Hypothesis By staying together
  the pair has higher fitness than by seeking other
  mates.
• Hippocampus (sea horses) where males carry the
  eggs for 20 days.
• Daily greeting ritual to assess condition of the
  males eggs.
• She is ready with more eggs when he gives birth

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Mate Guarding Hypothesis

• Females are hard to locate
• Females are receptive for brief periods
• Operational sex ratio is biased toward males
• Example Clown Shrimp Hymenocera picta

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Polyandry in Tibet
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Female Enforced Monogamy

• When female needs help in raising offspring
• Prevents her male from having additional females
• Yellow-breasted chat, for example

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11.4 Dual mate-enforced monogamy
11.4 Dual mate-enforced monogamy
11.4 Dual mate-enforced monogamy
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Monogamy in Mammals?

• Males rarely provide parental care (10 of the
  time)
• When parental care allows the male to have
  greater fitness than playing the field,
  monogamy will be the result
• Djungarian Hamsters, for example

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11.7 An exceptionally paternal rodent
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Paternal care in the California Mouse

• Normally monogamous species
• Experimentally remove the male or leave him there
• Three times more young emerge from the nest with
  father present

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Monogamy in Birds

• Most species of birds are socially monogamous
  because of mate assistance effects
• Many of the species engage in extra-pair
  copulations--EPCs

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Monogamous Males, Polyandrous Females

• Ecological conditions result in females looking
  and acting more like males
• Males provide parental care

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Spotted Sandpiper (Actitus macularia)

• Females are larger than males
• Females arrive at breeding grounds first
• Females fight for best territories
• Male arrives and she produces a clutch of not
  more than 4 eggs
• He can handle 4 or less by himself

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Ecological Factors in Sandpiper Mating System

• Adult sex ratio biased towards males
• There is a superabundant food source (mayfly
  hatches)
• A single parent can care for a clutch as well as
  a pair
• Young are precocial
• First arriving male may get extra fitness due to
  sperm storage by female

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Why EPCs?

• For males its a no brainer. He gets extra
  offspring that another male has to care for.
• For females Genetic Benefits and Material
  Benefits versus Costs

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Cost of EPCs or Polyandry

• Time spent searching for a suitable extra-pair
  mate
• Primary male may find out and leave or otherwise
  punish the female
• Socially transmitted diseases Predicts stronger
  immune system for greater degree of polyandry
  (primate white blood cells)

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Genetic Benefits

• Fertility insurance hypothesis
• Multiple eggs, more than one males sperm may be
  useful
• Polyandrous yellow-toothed cavy

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Genetic Benefits

• Good Genes Hypothesis
• Top quality males produce top quality offspring
• Male cricket who is successful in obtaining
  matings with female produce offspring who are
  more successful. The sexy sons effect.

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Genetic Benefits

• Genetic Compatibility Hypothesis
• Heterozygosity can be a good thing
• Homozygosity is like inbreeding and can produce
  undesireable effects
• Offspring of female bluethroats (bird) had
  stronger immune response from extra-pair male
  than mated male

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Material Benefits of Polyandry

• Access to a territory and protection from
  foreign males in red-wing blackbirds
• More matingsmore spermatophoresbigger and more
  successful clutches (Morman cricket and other
  insects)
• Prevent infanticide
• Get extra male help at the nest (Dunnocks and
  female manipulation of male)

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Polygynous Mating Systems

• Male has more than one female to mate with
• Mammals are common
• Male help raising offspring usually does not
  exist

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Resource Defense Polygyny

• Males control a resource that females need
• Southern Elephant Seals control the beach on
  which females give birth
• She mates after giving birth, therefore he has a
  harem
• Male Siamese Fighting Fish builds a nest that
  attracts females

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Polygyny Threshold Model

• A female may be better off becoming the second
  wife if the males territory is rich and allows
  her to raise more offspring than if she paired
  with a mail who had a poor territory
• Pied Flycatcher may take an already mated male
  even though they dont do as well as monogamous
  female

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Female Defense Polygyny

• When females gather together, a male will try to
  take over
• Lion prides are groups of females with a hunting
  territory and defense against roving males
  committing infanticide
• Marine Amphipods glue shells and rocks to
  themselves, and males may glue up to three
  females to themselves

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Scramble Competition Polygyny

• Males search for females that are not clumped
  together
• More persistent searching yields better results

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Thirteen-lined Ground Squirrels

• Females live in fairly spaced-out groupings
• Males make the rounds visiting female burrow
  sites
• Male uses spatial memory to return to females who
  are about to enter estrus
• Experiment Remove near estrus female and control
  female, not near estrus

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Explosive Breeding Assemblage

• Females become receptive for only a brief time
• They go to a breeding area when they are ready
• Males gather at the breeding location and compete
  for the female.
• Many species of frogs show this pattern

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Lek Polygyny

• The singles bar of the non-human world
• Males gather at a traditional mating site (lek)
• Females come willingly to the lek
• Males display for the females
• Female chooses her man
• There is nothing of material value associated
  with the lek

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Lek Phenomena

• Leks can be spread out as in the satin bowerbird
• Leks can be very compact as in white collared
  manakins and red deer
• A few males have high success rates, while other
  are low
• Leks form because males cannot monopolize females
  (why not scramble competition?)

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White collared manakin
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Lek Polygyny

• Red Deer

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Grackles displaying
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Three Lek Mate Choice Hypotheses

• Hotshot hypothesis Male with the best display
  gets the females, female likes it because she can
  shop for the best
• Hotspot hypothesis The location of a male in the
  lek determines his success. White bearded manakin
  females choose males in the center of the lek
• Female preference hypothesis She wants a lot of
  males for comparisons

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Black Grouse Leks

• Measured yearly success rates of males in
  different locations
• Found that most successful shifts from one season
  to the next
• Supports the Hotshot hypothesis

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Sage Grouse Leks

• Look at where males gather in leks and how
  females distribute themselves relative to the lek
• Data support the hotspot hypothesis
• http//www.r6.fws.gov/species/birds/sagegrouse/

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Why Leks?

• There may be more than one reason for a lek since
  different hypotheses have support
• Females may be able to minimize any potential
  damage roaming males may inflict in scramble
  competition
• The best males do really well

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Summary of Mating Systems

• Monogamy, polygyny, polyandry and
• Polygynandry!! (Its an orgy)
• Social monogamy vs. strict monogamy
• Ecological conditions influence which type of
  mating system exists for each species

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