Extra pair copulation vs. polyandrypolygamy

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Extra pair copulation vs. polyandry/polygamy

• EPC copulations that occur outside an
  identifiable reproductive pair
• The pair must be sharing non-copulatory
  reproductive efforts
• Even if disproportional
• The extra pair copulation must be against the
  will and wishes of the partner.
• i.e. cheating
• Should not result in diversion of significant
  parental resources from cheater
• Polyandry and polygamy on the other hand
• Can occur even in the presence of a pair bond
  relationship
• Would not be disputed by the partner
• Can cost the other partner in terms of fitness
  (short-term or overall)
• Typically results in division of parental
  resources

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Extra pair copulations (EPC)
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EPC advantages

• Males
• More offspring
• Mix genes with a greater variety of females
• Increased fecundity (reproductive capacity)
• Females
• Access to better genes
• Increased probability of fertility
• Increased gene compatibility

Partner disadvantages

• Males
• Wasted parental effort
• Decreased fecundity
• Females
• Potential loss of paternal effort
• Potential loss of paternally controlled resources

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• Polygyny advantages
• Males
• Access to more females
• Mix genes with a greater variety of females
• Increased fecundity
• Females
• Access to dominant males (good genes)
• If females are related they can share..
• territory defense responsibility
• offspring defense responsibility
• Partner disadvantages
• Males must typically defend
• Reproductive rights
• Territory/resources
• Failure can lead to infanticidal acts against his
  offspring
• Females typically loose
• Reproductive freedom of choice
• Decreased paternal effort as a function of harem
  size.
• Change in dominant male can lead to loss of
  offspring

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Polyandry generally speaking is rare and usually
occurs when females or resources are in extremely
short supply
Polyandry advantages Males Some access to
females (you dont play you cant win) Submission
to this strategy increased fecundity Shared
defense of offspring Shared defense of resources
Females Access to more males Mix genes with a
greater variety of males Increased fecundity
Partner disadvantages Males No or low mate
selection opportunity Paternal uncertainty Wasted
paternal effort Females May have to assume roles
typical of males such as Harem defense Offspring
defense
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A final note on polygyny polyandry and monogamy
There are many varieties of these basic mating
systems identified some of which are described in
the book. The name of each system is based on
the hypothetical key factor that is believed to
have been the evolutionary force behind the
evolution of that specific system.
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For example Lek polygamy

• Males collect in a very restricted physical space
• Lek position/formation does appears to correlate
  to density of females/ nesting areas
• Lek position tends to be relatively stable
  annually
• This position is poorly corrleated to resources
• Typically males of these species are ornately
  decorated
• Males will perform ritualistic displays
• Dances
• Plumage displays
• Ritualistic fights
• Females enter the lek, observe, then select a
  mate
• Typically a relatively few males are
  reproductively successful
• Males typically provide resources or parental
  effort

Sage Grouse
Prairie Chicken
Lordotus bee fly
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Fallow deer population density-dependent lek
polygyny

• Fallow deer exhibit typical polygynous behavior
• dominant male holds/defends and reproduces with a
  harem
• Under conditions of high population density
• Males move to common rut place (October)
• Each male defends and marks a small stand within
  place
• Females approach rut place.
• Dominant males in middle copulate.
• May start with lekking followed by harem holding
• only 10 males in a lek will mate

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  The bee fly Lordotus pulchrissimus

• Arial leks
• Are in the same place daily and annually
• Position cue have not been discovered
• No apparent correlation to shrub position
• No evidence of pheromone cues

9 lek sites in a 400 m by 700 m have persisted
for 5 years