Dynamic egg color mimicry

Abstract

Evolutionary hypotheses regarding the function of eggshell phenotypes, from solar protection through mimicry, have implicitly assumed that eggshell appearance remains static throughout the laying and incubation periods. However, recent research demonstrates that egg coloration changes over relatively short, biologically relevant timescales. Here, we provide the first evidence that such changes impact brood parasite–host eggshell color mimicry during the incubation stage. First, we use long‐term data to establish how rapidly the Acrocephalus arundinaceus Linnaeus (great reed warbler) responded to natural parasitic eggs laid by the Cuculus canorus Linnaeus (common cuckoo). Most hosts rejected parasitic eggs just prior to clutch completion, but the host response period extended well into incubation (~10 days after clutch completion). Using reflectance spectrometry and visual modeling, we demonstrate that eggshell coloration in the great reed warbler and its brood parasite, the common cuckoo, changes rapidly, and the extent of eggshell color mimicry shifts dynamically over the host response period. Specifically, 4 days after being laid, the host should notice achromatic color changes to both cuckoo and warbler eggs, while chromatic color changes would be noticeable after 8 days. Furthermore, we demonstrate that the perceived match between host and cuckoo eggshell color worsened over the incubation period. These findings have important implications for parasite–host coevolution dynamics, because host egg discrimination may be aided by disparate temporal color changes in host and parasite eggs.

Daurian redstart Phoenicurus auroreus is a host for the common cuckoo Cuculus canorus during the second, but not the first cultch

“…A similar result was also found in the European common redstart [23, but see 19]. Desertion behavior as a defensive strategy against parasitism has been studied frequently [29,30]. However, nest desertion often occurs in small-sized hosts such as chipping sparrows Spizella passerina, meadow pipits (Anthus pratensis), and blue-grey gnatcatchers (Polioptila caerulea) that rarely eject parasite eggs [31][32][33].…”

Variation in multicomponent recognition cues alters egg rejection decisions: a test of the optimal acceptance threshold hypothesis

“…closer to the long-wave sensitive photoreceptor) than their average egg colour. Although we recognize that abandoned eggs may fade [57], we assumed that these abandoned eggs provided a reasonable estimate of host eggshell colour; mockingbirds do not respond to the vast majority of cowbird parasitism, and it is unlikely that those laying a particular colour egg would produce a particular type of response. To test egg rejection along the blue -green to brown eggshell colour gradient, the JNDs between bluer eggs and the average host egg were multiplied by 21, while JNDs between browner eggs and the average host egg were multiplied by 1.…”

Grey Gerygone hosts are not egg rejecters, but Shining Bronze-Cuckoos lay cryptic eggs

“…The collection date (year) was known for all eggs except 6 cuckoo eggs (Shining Bronze-Cuckoo: range ¼ 1879-2010, median ¼ 1951, IQR ¼ 52.5 yr; Grey Gerygone: range ¼ 1889-1991, median ¼ 1904, IQR ¼ 46 yr). Minimal fading of egg coloration occurs in museum collections (Cassey et al 2010, Hanley et al 2013, although fading does take place during incubation (Hanley et al 2016). To be conservative, we repeated analyses of egg conspicuousness without including measurements taken from eggs laid at our field site.…”