The phosphate‐rich cover on the eggshells of grebes (Aves: Podicipitiformes)

Abstract

Spheres of a nut‐like morphology–a “kernel” formed from spherules contained in a “shell” of globular sub‐units–were a unique feature of the cover on the eggshells of six species of the order Podicipitiformes: Red‐necked grebe (Podiceps grisegend), Great crested grebe (Podiceps cristatus), Little grebe (Tachybaptus ruficollis), Black‐necked grebe (Podiceps nigrkollis), Slavonian grebe (Podiceps auritus) and Pied‐billed grebe (Podilymbus podiceps). The spheres did not give a pattern with X‐ray diffraction; the innermost ones were embedded in the dense crystalline layer on the outer surface of the calcitic portion of the shell. Electron‐probe microanalysis revealed that the cover of spheres contained principally oxygen, calcium, phosphorus and sulphur and infra‐red analysis demonstrated the presence of phosphate. The outer surface of the stratum of spheres was bounded by a thin, fissured layer of amorphous material. These observations raise questions about the ionic environment obtaining in the shell gland towards the end of shell formation and the adaptive significance of the cover on the eggshells of members of the Podicipitiformes.

The biomechanical, chemical, and physiological adaptations of the eggs of two Australian megapodes to their nesting strategies and their implications for extinct titanosaur dinosaurs

“…4), indicating that the primary mineral component of this accessory layer is calcium phosphate, as previously suggested by Board et al (1981). This accessory layer, previously reported by Board (Tullett et al, 1976;Board et al, 1984), in addition to the Guinea fowl (Board et al, 1982), possess the same chemical and crystallographic accessory layer as L. ocellata. However, dromornithids, Crax mitu, Anseranas semipalmata, Cereopsis novaehollandiae, and Cygnus atratus also possess an accessory layer of calcium phosphate, albeit with minor crystallographic differences in contrast to other avian eggs with vaterite (Tullett et al, 1976) or a waxy covering (Thompson and Goldie, 1990).…”

Antimicrobial properties of a nanostructured eggshell from a compost-nesting bird

“…Elemental analysis showed high concentrations of phosphorus on the layer of spheres of the brush-turkey cuticle, which likely corresponds to the presence of calcium phosphate (Board, 1982). A cuticle composed of calcium phosphate is rare compared with the more common calcium carbonate (vaterite) or the most ubiquitous organic cuticle (glycoprotein), and has only been found in eggshell cuticles of greater flamingos and guinea fowl (Tullett et al, 1976), grebes (Board et al, 1984) and Mallee fowl . Unlike glycoproteins and vaterite, calcium phosphate does not dissolve in water and thus would not be easily destroyed by exposure to rain or mud in the nest.…”

The biomechanical, chemical and physiological adaptations of the eggs of two Australian megapodes to their nesting strategies and their implications for extinct titanosaur dinosaurs

“…() in A. lathami , has antimicrobial properties that prevent infection of the developing embryo in the wet nesting environment (D'Alba et al ., ). Although, accessory layers are not rare in avian eggs, the clade Podicipedidae+Phoenicopteridae (Tullett et al ., ; Board et al ., ), in addition to the Guinea fowl (Board et al ., ), possess the same chemical and crystallographic accessory layer as L. ocellata . However, dromornithids, Crax mitu , Anseranas semipalmata , Cereopsis novaehollandiae and Cygnus atratus also possess an accessory layer of calcium phosphate, albeit with minor crystallographic differences (Grellet‐Tinner et al ., ) in contrast to other avian eggs with vaterite (Tullett et al ., ) or a waxy covering (Thompson & Goldie, ).…”