Maternal influence on eggshell maculation: implications for cryptic camouflaged eggs

Speckled and plain regions of avian eggshells differ in maternal deposition of calcium and metals: A hitherto overlooked chemical aspect of egg maculation

“…Presumably, therefore, the absolute pigment content cannot be evaluated correctly by any attempt at a visual description of an eggshell's external pigmentation (e.g., Brulez et al 2014, Pike 2015. It thus appears that this overlooked mechanism of pigment deposition through a thickening of its layer can better explain some conflicting results published earlier-for example, that the greater number of visible brown spots on quail eggshells is not due to enhanced protoporphyrin deposition (Duval et al 2016). It should also be borne in mind that, apart from the elements or contaminants deposited in eggshells, a portion of these maternal resources is accumulated in the egg contents; a positive relationship has been reported between the level of pesticide residues measured in egg contents and the greenness of the ground color related to biliverdin pigment (Jagannath et al 2008, Hanley andDoucet 2012).…”

“…Our results contradict those of previous investigations, probably because we selected a species with a different eggshell pigmentation structure-quail eggs have a thick superficial layer, compared to some other birds' eggs that have a thin internalized or superficial layer (cf. Duval et al 2016). However, it seems that a thick superficial pigment layer (such as in the quail) does not contradict the concept that maculation strengthens the eggshell (Gosler et al 2005).…”

“…Quail eggs have been used as a model in many previous experimental investigations to examine the maternal and environmental effects of variation in egg coloration in the context of the deposition of 2 basic eggshell pigments and to analyze the sources of variation in egg coloration patterns and pigment spot distributions. Female quails can promptly adapt the coloration of their eggs both to body condition (more heavily maculated eggs are laid by females with a poorer body condition; Duval et al 2013Duval et al , 2016 and to darkly colored substrates (Lovell et al 2013); such eggs are characterized by a greater hatchability and lower embryonic mortality (Taha 2011, Hassan et al 2013). Very recently, Duval et al (2016) reported some conflicting results on the role of speckling patterns in the accumulation of brown pigment in quail eggshells; they found that eggshell spot coverage was negatively correlated with the protoporphyrin concentration measured in entire eggshells, which suggests that protoporphyrin deposition does not increase the amount of visible brown spotting on the eggshell.…”

“…Female quails can promptly adapt the coloration of their eggs both to body condition (more heavily maculated eggs are laid by females with a poorer body condition; Duval et al 2013Duval et al , 2016 and to darkly colored substrates (Lovell et al 2013); such eggs are characterized by a greater hatchability and lower embryonic mortality (Taha 2011, Hassan et al 2013). Very recently, Duval et al (2016) reported some conflicting results on the role of speckling patterns in the accumulation of brown pigment in quail eggshells; they found that eggshell spot coverage was negatively correlated with the protoporphyrin concentration measured in entire eggshells, which suggests that protoporphyrin deposition does not increase the amount of visible brown spotting on the eggshell. It must be noted, however, that despite such multidimensional scientific interest in describing the causes or effects of variation in quail egg coloration, no data are available on variability in eggshell thickness in relation to the presence of maculation.…”

SpotEgg: an image‐processing tool for automatised analysis of colouration and spottiness

“…Many times, spottiness determination has simply relied on subjective human perception (Gosler et al , Sanz and García‐Navas ). In other cases, it has been determined by manually setting a threshold from the histogram of luminance of the input image (Duval et al , ), but this is also prone to observer's subjectivity. An unbiased detection of spots and background in eggshell digital images, as well as using reliable methods for colour analysis, is cornerstone to test the different functions proposed for avian eggshell pigmentation.…”