Male satin bowerbird painting and female choice
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Male satin bowerbird painting and female choiceJef Akst, Christy Bergeon,
and Emily Chester
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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 characteristicsSexual 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.
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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
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Bowerbirds (Ptilonorhynchidae)• Found in Australia & Indonesia
• 19 species – Catbirds - no bower, monogamous– Maypole/hut builders– Avenue builders
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Regent’s bowerbird Great bowerbird Satin bowerbird
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Bowers• Place for copulation• Built of sticks• Maypoles, huts, avenues• Associated with well-
decorated 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
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Satin bowerbirds(Ptilonorhynchus violaceus)
• 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
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• Male masticates plant material• Spreads mixture on inside walls of bower• Painting accounts for 24% of bower
maintenance time• Females nibble at painted twigs
Painting
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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
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Study Site
• Bunya Mountains (26°51’54”S, 151°35’15’’E)
• 160 km north-west of Brisbane, Australia
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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
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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
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Methods – Chemical ProfilesStir bar sorptive extraction methodMeasure both fresh paint and samples dried
for 24 hoursGas chromatography – mass spectrometry
J.Z. Zhang et al. (2005)
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Stir bar
Roller device
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Methods – Visual SpectraFull 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)
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Potential Outcomes
• Visual spectra– Correlation with chemical profile?
• Chemical profiles– Quality - different compounds identified– Quantity - variable strength of volatiles
• Male painting rate (Robson 2005)• Amount of paint (area, thickness)• Female nibbling rate• Freshness
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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