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?