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The Role of Ultraviolet Light in Defense of Brood Parasitism
by
Dawna Lee-Olsen
ECOL 484
Introduction
• Brood parasitism– host-parasite interactions are examples of co-
evolution– possibility of reduced fitness leads to
behavioral mechanisms to counteract• desertion• rejection• burial
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
UV Reflectance in Plumage
Zebra Finches
Blue Throats
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
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
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
Results (cont.)
• 1 study showed significant UV/greenness (PC3) oppoency between host-parasite eggs
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
Results (cont.)
• 1 study revealed cuckoo eggs mimicked hosts’ eggs in both spectral shape and brightness
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
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
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
Acknowledgements
• Dr. JodyLee Estrada Duek• Dr. Robert “Bill” Mannan
Questions??
Which eggs . . . are parasitic?