bowerbirds

Report
Male satin bowerbird
painting and female choice
Jef Akst, Christy Bergeon,
and Emily Chester
Sexual Selection Theory
• Within a species, one sex acts as a limiting
resource for the other
• Intrasexual selection - Competition
between individuals of the same sex for
access to mates
• Intersexual selection – Mate-choice
exhibited by the limiting sex
 exaggerated phenotypic characteristics
Sexual selection depends on the success of certain individuals over
others of the same sex, in relation to the propagation of the species;
while natural selection depends on the success of both sexes, at all ages,
in relation to the general conditions of life. --Charles Darwin, 1871.
Sex Roles
• Traditional sex roles
– Male-biased OSR, females are limiting sex
– Male: high competition, elaborate
ornamentation
– Female: high PI, more choosy
Competition between males for access
to females
Mate-choice exhibited by females
Bowerbirds (Ptilonorhynchidae)
• Found in Australia & Indonesia
• 19 species
– Catbirds - no bower, monogamous
– Maypole/hut builders
– Avenue builders
Regent’s bowerbird
Great bowerbird
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Satin bowerbird
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Bowers
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Place for copulation
Built of sticks
Maypoles, huts, avenues
Associated with welldecorated display courts
– Colorful natural and
artificial objects used for
decorations
• Important role in mate
attraction
• Attended year-round
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Bowers
Uy & Borgia 2000
Satin bowerbirds
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(Ptilonorhynchus violaceus)
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Found in rainforest of Eastern Australia
Polygynous
Create avenue bowers
Long-lived
– Males acquire adult plumage at 7 years
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Females are choosy!
• Visitations to bowers influenced by
– Male size
– Display rate
– Number of decorations
• Copulations influenced by
– Male size
– Painting rate
Painting
• Male masticates plant material
• Spreads mixture on inside walls of bower
• Painting accounts for 24% of bower
maintenance time
• Females nibble at painted twigs
Proposed research
Painting rate is positively correlated with male
mating success (Robson et al., 2005).
• Objectives:
– What aspects of painting rate influence female
mate choice?
• Approaches:
– Behavioral observations
– Visual and chemical characterization
Study Site
• Bunya Mountains (26°51’54”S,
151°35’15’’E)
• 160 km north-west of Brisbane, Australia
Methods
• Motion-sensitive cameras will be directed at male
bowers with a wide enough view to capture the
platform and entire bower area.
• We will measure:
– Time spent painting
– Total paint signal
• Percentage of bower paint cover
• Average thickness of paint
– Paint freshness = latency to female visitation
following male painting
– Rates of female nibbling = # nibbles/time in bower
Methods
• And look for correlations with:
– Male fitness = frequency of copulation =
number of copulations/time spent at bower
• Controlling for:
– Number of visits to bower by females
– Bower volume
– Number of decorations surrounding the
bower
Methods – Chemical Profiles
Stir bar sorptive extraction method
Measure both fresh paint and samples dried
for 24 hours
Gas chromatography – mass spectrometry
J.Z. Zhang et al. (2005)
Stir bar
Roller device
Methods – Visual Spectra
Full spectrum reflection spectrometer
Measure both fresh paint and samples dried for
24 hours under uniform light conditions
Principle Components Analysis
S. M. Doucet et al
(2006)
Potential Outcomes
• Visual spectra
– Correlation with chemical profile?
• Chemical profiles
– Quality - different compounds identified
– Quantity - variable strength of volatiles
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Male painting rate (Robson 2005)
Amount of paint (area, thickness)
Female nibbling rate
Freshness
Conclusion
• Identifying
characteristics of
paint that may be used in
female choice
• Future directions:
– Manipulations of paint
may demonstrate causal
relationships
– Measuring strength of
selection of female choice
may elucidate
mechanisms of bower
divergence

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