The Role of Ultraviolet Light in Defense of Brood Parasitism

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The Role of Ultraviolet Light in Defense of Brood
Parasitism

• by
• Dawna Lee-Olsen
• ECOL 484

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Introduction

• Brood parasitism
• host-parasite interactions are examples of
  co-evolution
• possibility of reduced fitness leads to
  behavioral mechanisms to counteract
• desertion
• rejection
• burial

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Introduction (cont.)

• Most birds have tetrachromatic vision
• 4 types of retinal cones (humans have 3)
• enables them to detect near UV wavelengths in the
  320-400nm range

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UV Reflectance in Plumage
Zebra Finches
Blue Throats
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Methods

• Literature review consists of 16 articles based
  on spectra reflectance on 300-700 nm range
• 12 studies on host intra-clutch variation
• 1 study examined role of color characteristics in
  egg recognition
• 2 studies used principal components analysis
  (PCA)
• 3 components brightness, brownness, and
  UV/greenness
• 1 study examined egg types of generalist cuckoo
  that parasitized several host species

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Results

• Host intra-clutch variation studies
• 3 studies support hypothesis that rejected host
  clutches are more dissimilar than accepted ones
• 2 studies support hypothesis that rejected
  clutches are less dissimilar
• 7 studies found no effect of intraclutch
  variation on rejection

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Results (cont.)

• Study on the blunt egg part found
• brightness reflected was lower in rejecters than
  accepters
• were darker in host clutches vs. rejected eggs
• were lighter in host clutches vs. accepted eggs

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Results (cont.)

• 1 study showed significant UV/greenness (PC3)
  oppoency between host-parasite eggs

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Results (cont.)

• 1 study showed common cuckoos populations match
  eggs of their hosts populations
• able to choose nests in which eggs similar to own

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Results (cont.)

• 1 study revealed cuckoo eggs mimicked hosts eggs
  in both spectral shape and brightness

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Discussion

• Compared to human vision, spectrometric measures
  provide good estimates of egg coloration
• Gain insight into egg matching previously hidden
• may need to evaluate model using artificial or
  painted eggs
• Disadvantage does not assess spatial pattern of
  maculation in eggs
• Ejected parasitic egg more dissimilar than
  accepted
• Hosts recognize eggs based on discordancy or
  true recognition
• Hosts reject eggs based on direct comparisons

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Discussion (cont.)

• Host egg discrimination possibly performed at
  certain wavelengths
• explains acceptance of nonmimetic eggs
• Other mechanisms at work
• hardwiring of avian visual system
• acceptance of nonmimetic eggs a function of
  different light environments
• spatial correlation of diet of hosts and
  parasites residing in same locality

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Discussion (cont.)

• Parasites such as cuckoos choose nests with eggs
  that closely match their own
• Could explain the lower levels of rejection in
  naturally parasitized nests
• Blunt egg part analysis reveals rejection of
  parasitic eggs in birds with lower variation in
  blue chroma
• Additional spectrometric studies needed
• Currently, use of spectrometric technology in
  conjunction with human vision a promising
  approach for investigating
• brood parasitism
• egg matching

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Acknowledgements

• Dr. JodyLee Estrada Duek
• Dr. Robert Bill Mannan

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Questions??
Which eggs . . .
are parasitic?