The Role of Ultraviolet Light in Defense of Brood Parasitism

1. The Role of Ultraviolet Light in Defense of Brood Parasitism by Dawna Lee-Olsen ECOL 484

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

3. 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

4. UV Reflectance in Plumage Zebra Finches Blue Throats

5. 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

6. 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

7. 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

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

9. 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

10. Results (cont.) • 1 study revealed cuckoo eggs mimicked hosts’ eggs in both spectral shape and brightness

11. 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

12. 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

13. 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

14. Acknowledgements • Dr. JodyLee Estrada Duek • Dr. Robert “Bill” Mannan

15. Questions?? Which eggs . . . are parasitic?