Egg discrimination along a gradient of natural variation in eggshell coloration.
Accurate recognition of salient cues is critical for adaptive responses, but the underlying sensory and cognitive processes are often poorly understood. For example, hosts of avian brood parasites have long been assumed to reject foreign eggs from their nests based on the total degree of dissimilarity in colour to their own eggs, regardless of the foreign eggs' colours. We tested hosts' responses to gradients of natural (blue-green to brown) and artificial (green to purple) egg colours, and demonstrate that hosts base rejection decisions on both the direction and degree of colour dissimilarity along the natural, but not artificial, gradient of egg colours. Hosts rejected brown eggs and accepted blue-green eggs along the natural egg colour gradient, irrespective of the total perceived dissimilarity from their own egg's colour. By contrast, their responses did not vary along the artificial colour gradient. Our results demonstrate that egg recognition is specifically tuned to the natural gradient of avian eggshell colour and suggest a novel decision rule. These results highlight the importance of considering sensory reception and decision rules when studying perception, and illustrate that our understanding of recognition processes benefits from examining natural variation in phenotypes.
Department of Biology, Long Island University - Post, Brookville, NY 11548-1300, USA daniel.hanley@liu.edu.
Daniel
0000-0003-0523-4335
D
Hanley
Department of Zoology and Laboratory of Ornithology, Palacký University, Olomouc 77146, Czech Republic.
Tomáš
T
Grim
Department of Biology, University of Akron, Akron, OH 44325, USA.|Division of Ecology and Evolution, Research School of Biology, Australian National University, Canberra 2601, Australia.
Branislav
B
Igic
Department of Zoology and Laboratory of Ornithology, Palacký University, Olomouc 77146, Czech Republic.
Peter
P
Samaš
Departamento de Ecología, Genética y Evolución, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, C1428EHA Buenos Aires, Argentina.
Analía V
AV
López
Department of Biology, University of Akron, Akron, OH 44325, USA.|Department of Biology, Evolution and Optics of Nanostructures Group, Ghent University, Ghent 9000, Belgium.
Matthew D
MD
Shawkey
Department of Psychology, Hunter College and the Graduate Center of the City University of New York, New York, NY 10065, USA.|Department of Animal Biology, School of Integrative Biology, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA.
Mark E
ME
Hauber
D000818:Animals; D001717:Birds; D003116:Color; D004528:Egg Shell; D009425:Nesting Behavior; D010063:Ovum
brood parasitism; colour perception; decision-making; egg discrimination; recognition