Abstract
Birds have evolved an astonishing diversity of egg pigmentation and this variation is driven by a complex interplay of proximate and ultimate factors. In ecological research, egg pigmentation is often measured at randomly selected points or regions of an eggshell, but it remains poorly explored whether and how spottiness and colouration are spatially consistent within a single egg. Here, we aimed to quantify consistency (repeatability) of spottiness patterns and background/spot colouration traits among the opposite lateral regions of an avian eggshell. For this purpose, we collected digital images of eggshells from three non-passerine birds showing different patterns of egg spottiness and colouration, i.e. Eurasian Coot Fulica atra, Black-headed Gull Chroicocephalus ridibundus, and Common Tern Sterna hirundo. We found an excellent within-egg repeatability (mean R > 0.90) of both background and spot colouration in all three species. In contrast, within-egg repeatability of spottiness traits was significantly lower, but the patterns of spatial variability were trait- and species-specific. While some spottiness traits showed relatively high within-egg repeatability (e.g. the total spot area), others were either poorly or moderately repeatable, depending on the species. Our results may have important practical implications for future research on eggshell colouration and spottiness, since measurements of reflectance spectra within a single region (side) are likely to be representative for the entire eggshell, while reliable characterisation of maculation may require replicate measurements across different eggshell regions. We recommend that the adaptive significance of spatial (within-egg) heterogeneity in avian eggshell pigmentation should be subject to further investigation under broader comparative framework.
Zusammenfassung
Rund ums Ei: Einheitlichkeit von Farbflecken und Hintergrundfarbe auf der Schale eines Vogeleis
Vögel haben eine erstaunliche Vielfalt an Eipigmentierungen entwickelt, bedingt durch ein komplexes Zusammenspiel von mittelbaren und unmittelbaren Faktoren. In der ökologischen Forschung wird die Pigmentierung von Eiern häufig an zufällig ausgewählten Stellen oder Bereichen einer Eischale gemessen, aber man weiß noch wenig darüber, ob und wie räumlich konsistent Flecken und Färbung bei einem einzelnen Ei sind. In dieser Studie wollten wir die Beständigkeit (Wiederholbarkeit) von Fleckenmustern und Hintergrund-/Fleckenfärbungsmerkmalen auf den beiden gegenüberliegenden Seiten einer Vogeleischale quantifizieren. Hierfür sammelten wir digitale Bilder von Eierschalen dreier Nicht-Sperlingsvögel mit unterschiedlichen Mustern von Eiflecken und Pigmentierung: dem Blässhuhn Fulica atra, der Lachmöwe Chroicocephalus ridibundus und der Flussseeschwalbe Sterna hirundo. Bei allen drei Arten fanden wir sowohl für die Hintergrund- als auch für die Fleckenfärbung bei ein und demselben Ei eine hohe Wiederholgenauigkeit (mittlerer R > 0,90). Im Gegensatz dazu war die Wiederholgenauigkeit von bestimmten Fleckenmerkmalen bei ein und demselben Ei deutlich geringer, aber die Muster der räumlichen Verteilung waren merkmals- und artspezifisch. Während einige Fleckenmerkmale eine relativ hohe Wiederholgenauigkeit beim selben Ei aufwiesen (z. B. die Gesamtfläche der Flecken), wurden andere Merkmale je nach Art schlecht oder kaum wiederholt. Unsere Ergebnisse könnten wichtige praktische Auswirkungen auf die künftige Forschung zur Färbung und Fleckigkeit von Eierschalen haben, da Messungen von Reflexionsspektren für eine Seite des Eies wahrscheinlich repräsentativ für die gesamte Eierschale sind, während eine zuverlässige Charakterisierung der Fleckenbildung möglicherweise wiederholte Messungen über die gesamte Eierschale erfordert. Wir empfehlen, dass der Anpassungs-Nutzen der Vielfalt in der Pigmentierung von Vogeleiern (bei jeweils einem Ei) innerhalb eines breiteren vergleichenden Rahmens weiter untersucht werden sollte.
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The data used in this study are available from the corresponding authors upon request.
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We thank three anonymous reviewers for constructive comments on the earlier draft of the manuscript.
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JG designed the study, PM and TJ carried out the fieldwork, TJ performed the measurements, PM performed the statistical analyses, PM wrote the first draft of the manuscript, and all the authors revised the manuscript for intellectual content and approved the final version.
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Minias, P., Gómez, J. & Janiszewski, T. All around the egg: consistency of spottiness and colouration across an avian eggshell. J Ornithol (2024). https://doi.org/10.1007/s10336-024-02162-3
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DOI: https://doi.org/10.1007/s10336-024-02162-3