The Perceptual and Cognitive Processes That Govern Egg Rejection in Hosts of Avian Brood Parasites

Daniel Hanley,Samantha L Rutledge,Juliana Villa

doi:10.3389/fevo.2021.702934

Abstract

Hosts of avian brood parasites are under intense selective pressure to prevent or reduce the cost of parasitism. Many have evolved refined egg discrimination abilities, which can select for eggshell mimicry in their parasite. A classic assumption underlying these coevolutionary dynamics is that host egg recognition depends on the perceivable difference between their own eggs and those of their parasite. Over the past two decades, the receptor noise-limited (RNL) model has contributed to our understanding of these coevolutionary interactions by providing researchers a method to predict a host’s ability to discriminate a parasite’s egg from its own. Recent research has shown that some hosts are more likely to reject brown eggs than blue eggs, regardless of the perceived differences to their own. Such responses suggest that host egg recognition may be due to perceptual or cognitive processes not currently predictable by the RNL model. In this perspective, we discuss the potential value of using the RNL model as a null model to explore alternative perceptual processes and higher-order cognitive processes that could explain how and why some hosts make seemingly counter-intuitive decisions. Further, we outline experiments that should be fruitful for determining the perceptual and cognitive processing used by hosts for egg recognition tasks.

Highlights

Avian brood parasitism is an alternative reproductive strategy where one female lays her eggs in another bird’s nest, imposing the costs of rearing her young on a set of foster parents (Stevens, 2013)
The perceptual and cognitive processes governing host egg recognition are central to understanding host decision-making and coevolutionary arms races
Classic theory assumes that hosts can select for eggshell mimicry in the parasite by rejecting parasite eggs they perceive as dissimilar to their own (Dawkins and Krebs, 1979)

Summary

Introduction

Avian brood parasitism is an alternative reproductive strategy where one female lays her eggs in another bird’s nest, imposing the costs of rearing her young on a set of foster parents (Stevens, 2013). Hosts often evolve egg recognition abilities as a major line of defense against parasitism, which, in turn, can select for improved eggshell mimicry in their parasite and instigate a coevolutionary arms race (Dawkins and Krebs, 1979; Davies and Brooke, 1989; Stoddard and Stevens, 2011). Pioneering work by Stoddard and Stevens (2011) applied an avian receptor noise limited (RNL) model (Vorobyev and Osorio, 1998) to the common cuckoo, Cuculus canorus, and their respective hosts They found that hosts with strong recognition abilities were parasitized by cuckoos that laid eggs with refined eggshell mimicry (as predicted by the RNL model). These counterintuitive and, at times disparate, findings raise the question, “why have these hosts deviated from our null expectations”?

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Conclusion