Mating behaviour continued female choice

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Mating behaviour continuedfemale choice

• Lecture 10

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Summary

• Female dispersion influenced by resource
  distribution
• Male distribution influenced by female dispersion
• BUT, females are not passive participants
• Greater energy investment by females means they
  should make good decisions
• Select mates carefully

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Females should choose mates that

• Provide resources that maximize her reproductive
  success, or
• Pass on good genes to her offspring

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Monogamy vs polygamy
Polygamy (1 sex acquires multiple mates)
Monogamy (1 male 1 female)
Polygyny (1 male multiple females)
Polyandry 1 female multiple males)
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Mating systems

• Can be categorized along this continuum
• But there are numerous variations within each
  category
• Intra- and inter-species variation

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In many species

• e.g., Red-winged Blackbirds
• Males defend territories that contain resources
  that females need
• Females settle on the males territories which
  contain the required resources
• Resource defence polygyny

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Males with high quality territories

• Have higher mating success
• Mate with more females
• Father more offspring
• But females are not passive participants in the
  process

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Resource defence polygyny

• From what we have already learned about natural
  selection
• And the relative differences in energy invested
  by males and females
• We can predict that females should carefully
  assess male and/or territory quality before they
  settle

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Polygyny Threshold Model
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Polygyny Threshold Model
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Polygyny Threshold Model
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Polygyny Threshold Model
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Polygyny Threshold Model
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How can we apply this model

• Often difficult to quantify territory quality
• We may not know what attributes are critical to
  reproductive success

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But we can often rank territories

• Using features that have been shown to correlate
  with reproductive success
• Quality of nesting sites
• Abundance of resources
• Male settling patterns

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Predictions of the model
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Predictions of the model
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Predictions of the model
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Predictions of the model
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Patterns of occupancy

• Are consistent with the model
• Best territories are occupied first

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In resource defence polygyny

• Do females choose males or resources?
• Wrasses

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Wrasses

• Feed on ecoparasites
• In some species females remain attached to
  feeding sitesdefend territories from other
  females
• Males defend these sites (females territories)
  male territories encompass up to 6 females
  territories
• Do females then choose these sites or the males?

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Wrasses

• Removal experiments
• Remove replaced malesfemales remain attached
  to the same sites
• Remove replaced Femalessites changed
• Therefore females choose sites

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Female choice

• In other cases females appear to choose male
  characteristics
• Difficult to separate male quality from territory
  quality
• High quality males are associated with best
  territories

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Elaborate plumage in birds

• Darwin recognised that these traits seemed to
  function by attracting females
• They seemed to also have a survival disadvantage
• Energy to produce and maintain
• Increased risk of predation

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Theoretical paradox

• Why are these traits not eliminated by natural
  selection?
• Sexual selection is working in the opposite
  direction to natural selection
• How do such extreme examples like peacock
  feathers evolve
• Why do females prefer these traits?
• Why doesnt natural selection prevent these
  extremes?

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Hypothesis

• Runaway selection
• Good genes hypothesis

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What is the selective advantage to females?

• Runaway selection
• Trait may initially be adaptive
• e.g. females prefer males with longer tails
• Initially longer tails may make birds better
  fliers
• They females develop a preference for longer
  tails because there traits will be passed on to
  her sons

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What is the selective advantage to females

• Now males with longer tails have a double
  advantage
• Better fliers and more attractive to females

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Fisher Lande

• If a genetic preference for elaborate plumage by
  females is linked to the gene(s) involved in the
  production of the character in males
• Offspring that are produced will have both
• The elaborate plumage (males)
• Preference for males with the most elaborate
  plumage (females)

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Runaway selection
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Good genes hypothesis

• Elaborate traits provide information about the
  males qualityGood genes
• Elaborate plumage may correlate with
• Age
• Body size
• Energy reserves

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Male Guppies

• Wild guppies
• Large brightly coloured tails correlate with
  efficient feeding and that acquisition of high
  quality food

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Handicap hypothesis

• Males invest in traits that are handicaps
• The fact that they survive despite their
  handicaps indicates they have high quality genes

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Hamilton and Zuk Hypothesis

• A version of the handicap hypothesis
• Bright colours indicate resistance to parasites
• Data Found correlation between parasite load and
  plumage quality
• Blind experiment
• Bright plumage indicated parasite resistance

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Hamilton and Zuk Hypothesis

• Suggested that bright colours are an honest
  signal of resistance to parasites
• Birds are subject to a large number of blood
  parasites
• Only those that can cope with the parasites can
  fully express the plumage characteristics

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Other examplesBower Birds

• Males build and decorate bower
• Handicap has been moved to an external
  structure
• Females prefer the most elaborate bowers
• They are built by
• Older experienced males
• Larger males
• Males with the most energy to spare
• Males compete for decorations
• Rare decorations are preferred

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Marsh wrens

• Males build dummy nests
• Males with the most (or best) dummy nests attract
  the most mates

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Leks

• Males defend small territories
• No resources
• Females select mates based on display quality
• Nesting takes place elsewhere

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Alternate reproductive strategies

• Ocellated wrasse
• Four distinct male strategies
• A) Territorial
• B) Sneaker
• C) Intermediate
• D) Pirate

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Alternate reproductive strategies

• Bluegill, threespine stickleback and blue-headed
  wrasse
• Have territorial males and sneakers

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Alternate reproductive strategies

• Bluegill
• Separate strategies
• Genetically developmentally determined

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Alternate reproductive strategies

• Blue-headed wrasse
• Young males are making the best of a bad
  situation
• Too young and small to hold territories become
  sneakers
• males are both sneakers and territory holders in
  their lifetimes

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Alternate reproductive strategies

• Threespine stickleback
• Males switch back and forth
• All males hold territories and defend nests
• Sneak into neighbouring males territories if
  opportunities arise

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Nest parasitism

• Brown headed cowbirdObligate nest parasites
• Lay eggs in host species nests
• Unable to raise there own young

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Nest parasitism

• Goldeneye ducksFacultative nest parasites
• Capable or rearing young but will
  opportunistically lay extra eggs in nests of
  conspecifics

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Extra Pair Paternity

• We are just beginning to understand the true
  complexity of mating systems
• We now know that in monogamous species like tree
  swallows have significant proportions of there
  offspring sired by extra-pair matings
• Alternative female reproductive strategies?

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Other variations exist

• We will encounter some of them when we look at
• Cooperative breeding
• Parental investment

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Implications for conservation

• Where courtship and mating behaviour occurs may
  be only one habitat feature we need to consider
• e.g. Lek breeding species--the focus may be on
  the Lek but nesting requirements are equally
  important

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Implications for conservation

• Species with alternate reproductive strategies
• The focus may be on the territorial males but
  habitat requirements of sneakers are equally
  importantespecially if they are genetically
  distinct as in bluegills

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Implications for conservation

• Nest parasitism
• Needs to be considered
• When locating nest boxes
• Considering forest fragmentation