Eggshell spot scoring methods cannot be used as a reliable proxy to determine pigment quantity

Eggshell maculation of most passerines is due to the deposition of the pigment protoporphyrin which is produced during biosynthesis of blood haem. Its functional signifi cance has only received empirical attention in recent years. Th is interest has generated a number of hypotheses of which some remain untested partly because the quantifi cation of protoporphyrin is analytically challenging and can be prohibitively expensive. Many studies have therefore used the extent of eggshell spotting as a proxy for total eggshell protoporphyrin concentration, although this has not been formally tested. Pigment scoring involves recording visible eggshell pigment attributes, such as spot intensity, distribution and size. Since even immaculate eggs can contain some protoporphyrin, there remains doubt over the degree to which visible pigment correlates with total pigment content of the shell. In this study, we test whether visible pigment scoring can be used as a proxy for protoporphyrin concentration of an eggshell. We use pigmented eggshells of two common British passerine species to compare eggshell spot intensity, distribution and spot size (as used by the visual pigment scoring method) with direct measures of eggshell protoporphyrin concentration. In addition, we compared an alternative method of pigment scoring, the pixel pigment scoring method, using a computer programme to quantify the number of pixels exceeding a specifi ed colour threshold. We demonstrate that although results from both scoring methods were positively correlated with eggshell protoporphyrin concentrations, the correlations were not suffi ciently strong to be used as surrogates in studies where actual pigment concentrations are required

Maternal influence on eggshell maculation: implications for cryptic camouflaged eggs

Published online: 20 August 2015. Abstract in English and GermanEgg camouflage may explain the adaptive significance of avian eggshell pigmentation in ground-nesting species. Eggshell maculation (spots) is predominantly due to protoporphyrin, but both biliverdin (antioxidant) and protoporphyrin (pro-oxidant) may be present in spotted eggshells. Because of their role in oxidative stress, the deposition of eggshell pigments might be condition-dependent. However, because of the fitness benefits of eggshell coloration, cryptic eggshell appearance should be strongly conserved in ground-nesting species regardless of female condition and eggshell pigment concentrations. We investigated whether Japanese quails (Coturnix coturnix japonica) maintained eggshell maculation under food restriction. We quantified eggshell maculation (i.e., percentage of spot coverage) using digital photography, and both protoporphyrin and biliverdin concentrations of eggs laid by females either on a food-restricted or an ad libitum diet. Females on a high quality diet, which are known to decrease the deposition of eggshell protoporphyrin, decreased eggshell maculation compared with food-restricted females that maintained it. For the first time, we propose an experimental study which suggests that eggshell maculation depends on female body condition and that manipulating eggshell maculation may be the strategy used by females to potentially optimize egg camouflage. = Die Tarnung von Eiern könnte die adaptive Bedeutung der Pigmentierung der Eierschale bodenbrütender Vögel erklären. Die Befleckung der Eierschale ist hauptsächlich auf Protoporphyrin zurückzuführen, aber sowohl Biliverdin (ein Antioxidant) als auch Protoporphyrin (ein Prooxidant) können in gefleckten Eierschalen enthalten sein. Aufgrund der Rolle von Eierschalenpigmenten bei oxidativem Stress könnte ihre Einlagerung in die Eierschale konditionsabhängig sein. Aufgrund der Fitnessvorteile einer Färbung der Eierschale sollte ein kryptisches Aussehen der Eier bei Bodenbrütern jedoch hochkonserviert sein, unabhängig von der Kondition der Weibchen und der Konzentration der Eierschalenpigmente. Wir haben untersucht, ob Japanwachteln (Coturnix coturnix japonica) die Befleckung ihrer Eierschale bei Futterknappheit beibehielten. Wir haben die Eierschalenbefleckung (d.h. den Anteil der Abdeckung mit Flecken) mit Hilfe digitaler Fotografie quantifiziert sowie die Protoporphyrin- und Biliverdin-Konzentrationen der Eier von Weibchen ermittelt, die entweder eingeschränkt oder ad libitum Futter erhielten. Weibchen mit hochwertiger Kost, die bekannterweise die Einlagerung von Protoporphyrin in die Eierschale reduzieren, reduzierten die Befleckung der Eierschale im Vergleich zu Weibchen mit eingeschränkter Kost, welche sie beibehielten. Zum ersten Mal liefern wir eine experimentelle Studie ab, die darauf hindeutet, dass die Befleckung der Eierschale von der Kondition des Weibchens abhängt und dass Weibchen die Befleckung der Eierschale beeinflussen könnten, als Strategie, um die Tarnung der Eier potenziell zu optimieren.Camille Duval, Phillip Cassey, P. George Lovell, Ivan Mikšík, S. James Reynolds, Karen A. Spence