Birds' eggshells are renowned for their striking colours and varied patterns. Although often considered exceptionally diverse, we report that avian eggshell coloration, sampled here across the full phylogenetic diversity of birds, occupies only 0.08-0.10% of the avian perceivable colour space. The concentrations of the two known tetrapyrrole eggshell pigments (protoporphyrin and biliverdin) are generally poor predictors of colour, both intra- and interspecifically. Here, we show that the constrained diversity of eggshell coloration can be accurately predicted by colour mixing models based on the relative contribution of both pigments and we demonstrate that the models' predictions can be improved by accounting for the reflectance of the eggshell's calcium carbonate matrix. The establishment of these proximate links between pigmentation and colour will enable future tests of hypotheses on the functions of perceived avian eggshell colours that depend on eggshell chemistry. More generally, colour mixing models are not limited to avian eggshell colours but apply to any natural colour. Our approach illustrates how modelling can aid the understanding of constraints on phenotypic diversity.
- MeSH
- Pigmentation * MeSH
- Birds physiology MeSH
- Egg Shell physiology MeSH
- Visual Perception * MeSH
- Animals MeSH
- Check Tag
- Animals MeSH
- Publication type
- Journal Article MeSH
- Research Support, Non-U.S. Gov't MeSH
Avian eggshells are variable in appearance, including coloration. Here, we demonstrate that Raman spectroscopy can provide accurate diagnostic information about major eggshell constituents, including the pigments biliverdin and protoporphyrin IX. Eggshells pigmented with biliverdin showed a series of pigment-diagnostic Raman peaks under 785 nm excitation. Eggshells pigmented with protoporphyrin IX showed strong emission under 1064 nm and 785 nm excitation, whereas resonance Raman spectra (351 nm excitation) showed a set of protoporphyrin IX informative peaks characteristic of protoporphyrin IX. As representative examples, we identified biliverdin in the olive green eggshells of elegant crested tinamous (Eudromia elegans) and in the blue eggshells of extinct upland moa (Megalapteryx didinus). This study encourages the wider use of Raman spectroscopy in pigment and coloration research and highlights the value of this technique for non-destructive analyses of museum eggshell specimens.
The proteins and pigment of the eggshell of the Siamese crocodile (Crocodylus siamensis) were analysed. For proteomic analysis, various decalcification methods were used when the two main surface layers were analyzed. These layers are important for antimicrobial defense of egg (particularly the cuticle). We found 58 proteins in both layers, of which 4 were specific for the cuticle and 26 for the palisade (honeycomb) layer. Substantial differences between proteins in the eggshell of crocodile and previously described birds' eggshells exist (both in terms of quality and quantity), however, the entire proteome of Crocodilians has not been described yet. The most abundant protein was thyroglobulin. The role of determined proteins in the eggshell of the Siamese crocodile is discussed. For the first time, the presence of porphyrin pigment is reported in a crocodilian eggshell, albeit in a small amount (about 2 to 3 orders of magnitude lower than white avian eggs).
The organic components of bones and other mineralized tissues have a high impact on the organization and deposition of calcium, and consequently influence the mechanical properties of those tissues. The extractable proteins of avian eggshells have been studied extensively and many of them have been identified; insoluble (non-extractable) proteins have been sparsely studied, however. In the work discussed in this paper we studied EDTA-insoluble proteins by gradual decalcification of eggshell with EDTA. The insoluble proteinaceous films were chemically treated with cyanogen bromide and the mixtures of large fragments obtained were gradually precipitated with salt. The separated fractions were digested with trypsin and analyzed by HPLC-MS-MS (ion trap mass spectrometer). Analysis of the entire eggshell matrix (without precipitation steps) only enabled 6 proteins to be determined (ovocalyxins 32 and 36, ovocleidin 17 and 116, clusterin, and ovalbumin). Pretreatment of the individual eggshell layers and gradual precipitation with salt markedly increased the number of proteins identified - 28 proteins were determined. We identified for the first time collagens I (two chains) and III in the eggshell matrix, and Kunitz-like protease inhibitor as a major shell matrix protein. Besides the above mentioned proteins we can also mention EDIL3, fibronectin, sulfhydryl oxidase, tubulin alpha 1, lysozyme, Dickkopf-related protein 3, keratins, and ovotransferrin. The relative abundances of proteins in all eggshell layers were determined using the exponentially modified protein abundance index (emPAI). In the cuticle layer seven proteins were identified, whereas 16 proteins were described in the palisade layer and 23 in the mammillary layer.
Accurate recognition of salient cues is critical for adaptive responses, but the underlying sensory and cognitive processes are often poorly understood. For example, hosts of avian brood parasites have long been assumed to reject foreign eggs from their nests based on the total degree of dissimilarity in colour to their own eggs, regardless of the foreign eggs' colours. We tested hosts' responses to gradients of natural (blue-green to brown) and artificial (green to purple) egg colours, and demonstrate that hosts base rejection decisions on both the direction and degree of colour dissimilarity along the natural, but not artificial, gradient of egg colours. Hosts rejected brown eggs and accepted blue-green eggs along the natural egg colour gradient, irrespective of the total perceived dissimilarity from their own egg's colour. By contrast, their responses did not vary along the artificial colour gradient. Our results demonstrate that egg recognition is specifically tuned to the natural gradient of avian eggshell colour and suggest a novel decision rule. These results highlight the importance of considering sensory reception and decision rules when studying perception, and illustrate that our understanding of recognition processes benefits from examining natural variation in phenotypes.
Obligate avian brood parasitic species impose the costs of incubating foreign eggs and raising young upon their unrelated hosts. The most common host defence is the rejection of parasitic eggs from the nest. Both egg colours and spot patterns influence egg rejection decisions in many host species, yet no studies have explicitly examined the role of variation in spot coloration. We studied the American robin Turdus migratorius, a blue-green unspotted egg-laying host of the brown-headed cowbird Molothrus ater, a brood parasite that lays non-mimetic spotted eggs. We examined host responses to model eggs with variable spot coloration against a constant robin-mimetic ground colour to identify patterns of rejection associated with perceived contrast between spot and ground colours. By using avian visual modelling, we found that robins were more likely to reject eggs whose spots had greater chromatic (hue) but not achromatic (brightness) contrast. Therefore, egg rejection decision rules in the American robin may depend on the colour contrast between parasite eggshell spot and host ground coloration. Our study also suggests that egg recognition in relation to spot coloration, like ground colour recognition, is tuned to the natural variation of avian eggshell spot colours but not to unnatural spot colours.
- MeSH
- Nesting Behavior MeSH
- Ovum MeSH
- Egg Shell * MeSH
- Songbirds MeSH
- Animals MeSH
- Check Tag
- Animals MeSH
- Publication type
- Journal Article MeSH
Physiological constraints on colouration have been widely reported; especially in birds, which trade-off antioxidant responses against colourful costly signals. One female extended phenotypic trait, which might also highlight important physiological trade-offs, is the pigmentation of their eggshells. In ground-nesting species, producing eggs that are visually undetectable by predators is the best camouflage strategy. However, the condition-dependence of eggshell pigmentation, and the pigments role in oxidative stress, may constrain females to trade-off between their antioxidant capacity and maximising the camouflage of their eggs when they deposit eggshell pigments. Developmental stress is one factor that influences female antioxidant capacity, and could lead to variations in eggshell pigmentation that might have crucial consequences on individual fitness if egg crypsis is compromised especially under stressful conditions. We investigated the interaction between developmental and breeding conditions with respect to eggshell pigmentation in Japanese quail. We studied 30 females that bred under both control and stressful conditions, and were exposed to pre- and/or post-natal stress, or neither. Pre- and post-natal stress independently influenced eggshell pigmentation strategies under stressful breeding conditions. Under stressful reproduction, eggshell protoporphyrin concentration and maculation were affected by pre-natal stress, whereas eggshell reflectance and biliverdin concentration were influenced by post-natal stress. These changes may reflect potential adaptive strategies shaped by developmental stress, but additional data on the benefit of egg crypsis in quail, combined with studies on the role of both pigments on chick survival, will help to clarify whether early life stress can enhance fitness through eggshell pigmentation when developmental and reproductive environments match.
- MeSH
- Breeding MeSH
- Coturnix physiology MeSH
- Stress, Physiological * MeSH
- Animals, Newborn MeSH
- Pigmentation physiology MeSH
- Reproduction physiology MeSH
- Body Weight MeSH
- Egg Shell physiology MeSH
- Animals MeSH
- Check Tag
- Female MeSH
- Animals MeSH
- Publication type
- Journal Article MeSH
- Research Support, Non-U.S. Gov't MeSH
One of the most effective defenses against avian brood parasitism is the rejection of the foreign egg from the host's nest. Until recently, most studies have tested whether hosts discriminate between own and foreign eggs based on the absolute differences in avian-perceivable eggshell coloration and maculation. However, recent studies suggest that hosts may instead contrast egg appearances across a directional eggshell color gradient. We assessed which discrimination rule best explained egg rejection by great reed warblers Acrocephalus arundinaceus, a frequent host to an egg-mimetic race of common cuckoos Cuculus canorus. We deployed 3D-printed model eggs varying in blue-green to brown coloration and in the presence of maculation. Using visual modeling, we calculated the absolute chromatic and achromatic just-noticeable differences (JNDs), as well as directional JNDs across a blue-green to brown egg color gradient, between host and model eggs. While most model eggs were rejected by great reed warblers, browner eggs were rejected with higher probability than more blue-green eggs, and the rejection probability did not depend on maculation. Directional egg color discrimination shown here and in a suite of recent studies on other host species may shape the cognitive decision rules that hosts use to recognize foreign eggs and affect the course of evolution in parasitic egg mimicry.
- MeSH
- Color * MeSH
- Nesting Behavior physiology MeSH
- Passeriformes MeSH
- Egg Shell * MeSH
- Color Perception physiology MeSH
- Animals MeSH
- Check Tag
- Animals MeSH
- Publication type
- Journal Article MeSH
In practice, goose eggs are increasingly used and, therefore, the rheological properties have to be known for processing. The eggs of geese (Landes Goose, Anser anser f. domestica) were stored for one, 2, 3, 4, 6, and 8 wk at a constant temperature 4°C. First of all, the egg quality parameters were described in terms of egg weight, egg weight loss, egg shape index, yolk height, albumen height, yolk index, albumen index, and Haugh units. In the next step the rheological behavior of liquid egg products (egg yolk, albumen, and whole liquid egg) was studied using a concentric cylinder viscometer. Flow curves of all liquid egg products exhibited non-Newtonian shear thinning behavior. This behavior can be described using the Herschel-Bulkley model and for technical application using the Ostwald-de Waele model. The effect of the storage duration on the rheological behavior is different for the different liquid egg products. With the exception of very low shear rates, the viscosity of the egg yolk as well as of the whole liquid egg decreases with storage time. At lower shear rates there is a tendency toward increased albumen viscosity with storage duration. The storage duration also affects the mechanical properties of the eggshell membrane. This effect has been evaluated in terms of the ultimate tensile strength, fracture strain, and fracture toughness. All these parameters increased with the loading rate, but decreased during the egg storage. These mechanical phenomena should be respected, namely in the design of the egg model for the numerical simulation of the egg behavior under different kinds of the mechanical loading.
- MeSH
- Geese * MeSH
- Ovum physiology MeSH
- Rheology MeSH
- Food Storage * MeSH
- Egg Shell physiology MeSH
- Viscosity MeSH
- Animals MeSH
- Check Tag
- Animals MeSH
- Publication type
- Journal Article MeSH
Eggshell colour, quality, and biosafety of table eggs are of significant commercial interest. To date, there have been few studies investigating the relationship between eggshell pigmentation and internal egg quality in commercially bred birds. Moreover, the genetic basis and mechanisms behind the effects of extrinsic factors on deposition of antimicrobial compounds in egg white and eggshell pigments are not fully understood. In the present study, we evaluate the effect of chicken breed identity, eggshell pigmentation and the role of extrinsic factors (year and breeder identity) on variability in the concentrations of 2 major egg white antimicrobial proteins (AMPs), lysozyme (LSM), and ovotransferrin (OVOTR), across 23 traditional chicken breeds. We found that chicken breed identity and eggshell pigmentation explained most variability in the concentration of egg white LSM and OVOTR. Year and breeder identity were also significant predictors of egg white LSM and OVOTR variability, and showed selective effects on the deposition of both AMPs in egg white. We also documented a positive correlation between concentration of egg white LSM and eggshell cuticle protoporphyrin in tinted and dark brown eggs, but not in brown, white, and blue eggs. We assume that a combination of both intrinsic genetic and hormonally regulated extrinsic factors is responsible for this relationship and for the variability in egg white AMPs. In this study, we demonstrate the existence of a relationship between eggshell pigmentation and egg white AMPs content in the eggs of traditional chicken breeds that may advertise the egg's antimicrobial potential and biosafety. These findings provide novel insights into the relationship between eggshell pigmentation and egg internal quality and may stimulate the recovery and exploitation of traditional chicken breeds for egg production, where the demands for egg quality and biosafety, in conjunction with animal welfare, are a priority.
- MeSH
- Immunomodulation genetics MeSH
- Antimicrobial Cationic Peptides genetics metabolism MeSH
- Chickens genetics immunology metabolism MeSH
- Pigmentation MeSH
- Avian Proteins genetics metabolism MeSH
- Egg Shell chemistry MeSH
- Egg Proteins genetics metabolism MeSH
- Animals MeSH
- Check Tag
- Animals MeSH
- Publication type
- Journal Article MeSH
