Brood parasite and host eggshells undergo similar levels of decalcification during embryonic development

Common cuckoos (Cuculus canorus) are obligate brood parasites that lay their eggs in the nests of other (host) species. To increase the likelihood of successful parasitism, common cuckoos lay eggs with thicker and structurally stronger eggshells than those of their hosts and non-parasitic relatives. Although hatching from thicker eggshells requires greater effort and may impose physiological costs on cuckoo embryos during hatching, it is unclear whether cuckoo eggshells are indeed thicker at the time of hatching. This is because avian embryos decalcify the innermost eggshell layer (mammillary layer) for organ development during embryogenesis, reducing eggshell thickness and making hatching easier. Therefore, common cuckoo eggshells may undergo a greater degree of decalcification during embryonic development to facilitate hatching from an initially thicker-shelled egg. We used scanning electron microscopy to test this hypothesis by comparing the thickness and degree of decalcification of eggshells collected either before incubation or after hatching. We found that cuckoo eggshells undergo similar degrees of decalcification during embryonic development as the thinner eggshells of a host that lays similarly sized eggs, the great reed warbler (Acrocephalus arundinaceus). Cuckoo eggshells hence remain thicker than eggshells of this host throughout embryogenesis, supporting the predicted trade-off between the benefits of laying puncture resistant eggs and the physiological costs associated with hatching

A comparative study of the exchange in vivo of major constituents of bone mineral.

Groups of young and old rats were injected with a variety of labelled substanzes (urea, Cl-, K+, Na+, HCO3-, PO43-, Ca++). Data for Mg++ were taken from the literature. One and a half hours later, compact shafts of long bones were removed and cleaned scrupulously, and analyses were performed for both "cold" and isotopic concentrations of substances. This time point was chosen to insure equilibration of the aqueous phase of bone while minimizing contributions from surface exchange, recrystallization, solid diffusion, growth or resorption. With fixed variables of time, species, bone specimen, and methodology, uambiguous comparisons of the exchange in bone could be made between the many substances studied. The exchange data could be divided into three categories: a) complete exchange (urea Cl-, and K+); b) partial exchange, decreasing variably with age (Na+, CO2, and Mg++); and c) minimal exchange (Ca++ and PO43-). Clearly the traditional classification of "available" and "unavailable" skeleton is ambiguous and determined by the conditions and the ion or substance chosen for study. Clearly also, a new overall concept of bone exchange in vivo is badly needed. Calculations of the apparent concentration of the various electrolytes in bone water reveal that the aqueous phase of bone has a composition markedly different from plasma water. In particular, the concentration of potassium in bone water was found to be remarkably high. © 1968 Springer-Verlag

A comparative study of the exchange in vivo of major constituents of bone mineral

Groups of young and old rats were injected with a variety of labelled substanzes (urea, Cl-, K+, Na+, HCO3-, PO43-, Ca++). Data for Mg++ were taken from the literature. One and a half hours later, compact shafts of long bones were removed and cleaned scrupulously, and analyses were performed for both "cold" and isotopic concentrations of substances. This time point was chosen to insure equilibration of the aqueous phase of bone while minimizing contributions from surface exchange, recrystallization, solid diffusion, growth or resorption. With fixed variables of time, species, bone specimen, and methodology, uambiguous comparisons of the exchange in bone could be made between the many substances studied. The exchange data could be divided into three categories: a) complete exchange (urea Cl-, and K+); b) partial exchange, decreasing variably with age (Na+, CO2, and Mg++); and c) minimal exchange (Ca++ and PO43-). Clearly the traditional classification of "available" and "unavailable" skeleton is ambiguous and determined by the conditions and the ion or substance chosen for study. Clearly also, a new overall concept of bone exchange in vivo is badly needed. Calculations of the apparent concentration of the various electrolytes in bone water reveal that the aqueous phase of bone has a composition markedly different from plasma water. In particular, the concentration of potassium in bone water was found to be remarkably high. © 1968 Springer-Verlag

The cycling concept of exchange in bone.

An hypothesis has been developed to explain in a semi-quantitative fashion the wide variations in time required for the equilibration in the skeleton of various radioactive substances when they are introduced into the circulation. The basis for the hypothesis rests on the assumption that three variables define the rate-limiting step in bone exchange: a) the rate of perfusion of bone, b) the concentration of the ion plasma, and c) the concentration of the ion in bone. Using this idea and data from the literature, "cycling times" were calculated for Cl-, Na+, K+, and Ca++. They were found to vary by four orders of magnitude (from 10 min for Cl- to 64 days for Ca++ in the rat). These predictions were tested for22Na- and45Ca-exchange in a column of apatite mineral in vitro. In vivo36Cl- and42K-exchange in rat femur was studied. The blood disappearance of22Na in man was also examined. Finally, data in the literture of45Ca-exchange in the rat molar was redrawn. In every case, experimental results closely approximated the predictions of the cycling concept. Some of the implications of these findings are briefly discussed. © 1968 Springer-Verlag

The cycling concept of exchange in bone.

An hypothesis has been developed to explain in a semi-quantitative fashion the wide variations in time required for the equilibration in the skeleton of various radioactive substances when they are introduced into the circulation. The basis for the hypothesis rests on the assumption that three variables define the rate-limiting step in bone exchange: a) the rate of perfusion of bone, b) the concentration of the ion plasma, and c) the concentration of the ion in bone. Using this idea and data from the literature, "cycling times" were calculated for Cl-, Na+, K+, and Ca++. They were found to vary by four orders of magnitude (from 10 min for Cl- to 64 days for Ca++ in the rat). These predictions were tested for22Na- and45Ca-exchange in a column of apatite mineral in vitro. In vivo36Cl- and42K-exchange in rat femur was studied. The blood disappearance of22Na in man was also examined. Finally, data in the literture of45Ca-exchange in the rat molar was redrawn. In every case, experimental results closely approximated the predictions of the cycling concept. Some of the implications of these findings are briefly discussed. © 1968 Springer-Verlag