Egg discrimination along a gradient of natural variation in eggshell coloration.

Daniel Hanley,Branislav Igic,Tomáš Grim,Matthew D Shawkey,Peter Samaš,Mark E Hauber,Analía V López

doi:10.1098/rspb.2016.2592

Abstract

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.

Highlights

The recognition of suitable food, mates, predators, and shelter is central to all life
We introduced a single foreign egg model into each nest and recorded whether or not the attending female was flushed from the nest [23]; these eggs were unspotted immaculate and their colours uniquely positioned along a gradient of blue-green to brown colour variation representative of natural avian eggshell colours [16] or an alternative orthogonal gradient varying from green to purple
We provide experimental evidence that host response to parasitic eggshell colour is not solely based on the perceived colour difference between their own and parasitic eggs as previously thought

Summary

Introduction

The recognition of suitable food, mates, predators, and shelter is central to all life. Most studies (electronic supplementary material, table S1) have examined host responses based on the absolute perceived colour dissimilarity between host and parasitic eggs (hereafter, the multiple threshold decision rule; figure 1a).

Results

Conclusion