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The Role of Ultraviolet Light in Defense of Brood Parasitism
byDawna 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 host’s 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?