Journal
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Volume 107, Issue 19, Pages 8672-8676Publisher
NATL ACAD SCIENCES
DOI: 10.1073/pnas.0910486107
Keywords
brood parasitism; coevolution; egg color; egg pattern; vision
Categories
Funding
- Royal Society
- Sidney Sussex College
- Newnham College, Cambridge
- DST/NRF Centre of Excellence at the Percy FitzPatrick Institute
- University of Cape Town
- Biotechnology and Biological Sciences Research Council [BB/G022887/1]
- Girton College, Cambridge
- Biotechnology and Biological Sciences Research Council [BB/G022887/1] Funding Source: researchfish
- BBSRC [BB/G022887/1] Funding Source: UKRI
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One of the most striking outcomes of coevolution between species is egg mimicry by brood parasitic birds, resulting from rejection behavior by discriminating host parents. Yet, how exactly does a host detect a parasitic egg? Brood parasitism and egg rejection behavior provide a model system for exploring the relative importance of different visual cues used in a behavioral task. Although hosts are discriminating, we do not know exactly what cues they use, and to answer this it is crucial to account for the receiver's visual perception. Color, luminance (perceived lightness) and pattern information have never been simultaneously quantified and experimentally tested through a bird's eye. The cuckoo finch Anomalo-spiza imberbis and its hosts show spectacular polymorphisms in egg appearance, providing a good opportunity for investigating visual discrimination owing to the large range of patterns and colors involved. Here we combine field experiments in Africa with modeling of avian color vision and pattern discrimination to identify the specific visual cues used by hosts in making rejection decisions. We found that disparity between host and foreign eggs in both color and several aspects of pattern (dispersion, principal marking size, and variability in marking size) were important predictors of rejection, especially color. These cues correspond exactly to the principal differences between host and parasitic eggs, showing that hosts use the most reliable available cues in making rejection decisions, and select for parasitic eggs that are increasingly mimetic in a range of visual attributes.
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