G.C Whittow

Metabolic responses of chicken embryos and hatchlings to altered O2 environments

The oxygen consumption (MO2) response over a 4 h period of exposure to altered ambient O2 (air, 10, 15, 40, 60, 80 and 100%), helium (He) and sulfur hexafluoride (SF6) environments was determined for young (12 days old) and late (16 and 18 days old) embryos, externally pipped (EP) eggs and just hatched chicks (hatchlings) of the domestic fowl. The young embryos were insensitive to hyperoxic gas mixtures and to He exposure, while the late embryos increase their MO2 in hyperoxic environments, independently of O2 concentration, and also in a He atmosphere. Both the young and late embryos responded to SF6 exposure with decreasing MO2, as SF6 reduces O2 diffusivity through the eggshell. The MO2 of EP eggs and hatchlings in He and SF6 varied very widely, the effects of altered diffusivity being insignificant. In hypoxic environments in which the MO2 decreased, the fall of MO2 became smaller as embryos developed and particularly after they pipped the shell and hatched. In an atmosphere of 10% O2, the MO2 of all embryos in the egg before hatching decreased to below 10% of the control after 4 h, while in hatchlings the MO2 remained above 80% of the control. As all embryos in situ in the egg depend entirely or partly on diffusion in order to obtain O2, this emphasizes the limitation of the diffusive process. A 4 h exposure to 10% O2 was lethal for embryos in the egg even if they had pipped the shell and were breathing air with the lungs.

Metabolic responses of chicken embryos to graded, prolonged alterations in ambient temperature.

1. Chicken embryos aged 12, 16, 18 and 20 (externally pipped) days of incubation were exposed to graded reductions (2 degrees C) in ambient temperature from 38 to 28 degrees C, exposure to each temperature lasting up to 9 hr. 2. Oxygen uptake was measured first at 38 degrees C and then in the quasi-equilibrium state at lowered temperatures. The temperature coefficient (Q10) was calculated for each egg. 3. For mild cooling (32 degrees C), the Q10 in 18-day-old embryos was about 1.5, while 12- and 16-day-old embryos had a Q10 value of about 2, indicating that a feeble homeothermic metabolic response to cooling appears in late prenatal embryos. It became more marked in externally pipped embryos and further augmented in hatchlings.

Noncontact measurements of avian embryo heart rate by means of the laser speckle: comparison with contact measurements

A new, noncontact system for measuring the heart rate of avian embryos in the egg has been developed using a laser speckle phenomenon. The system was based upon detection of egg movements attributable to cardiac contractions of the embryo by measuring the intensity fluctuation of speckle produced in the proximity of the egg under laser light illumination (i.e. noncontact measurement). The applicability of the noncontact system to determine the heart rate of developing chick embryos was examined simultaneously with a contact system employing an audio cartridge. Both systems were found to be feasible in determining the heart rate of embryos during the late prenatal and paranatal stages. With the aid of adeques signal processing, the measurement of cardiogenic movements of the egg can be used to count the heart rate during the middle stages of incubation.

Simple, noninvasive system for measuring the heart rate of avian embryos and hatchlings by means of a piezoelectric film

Using a flexible piezoelectric film, the authors developed a simple system to determine noninvasively the heart rate of chicken embryos and hatchlings. The film was piezoelectric polyvinylidene fluoride (PVDF), which is sensitive enough to detect cardiogenic ballistic movements of the egg (ballistocardiogram (BCG)) and precordial movements of the hatchling attributable to cardiac contractions (apexcardiogram (ACG)). The BCG could be detected, during the second half of incubation, by placing the egg on the PVDF film on a soft substrate. The detected signal was found to be a measure of movement velocity. The ACG could be measured when the hatchlings chest wall made contact with the PVDF film installed in a box in which the hatchling was confined. The heart rate was counted from the lag time of autocorrelation calculated for a certain time segment (e.g. 2s) of the BCG and ACG recordings.

Comparative metabolic responses to prolonged cooling in precocial duck (Anas domestica) and altricial pigeon (Columba domestica) embryos

1. Embryos and hatchlings of the duck and pigeon were exposed to a lowered temperature for 6 hr. The oxygen consumption (MO2) was measured before and after cooling and the ratio of the two was compared with that predicted for a temperature coefficient of 2 (Arrhenius value). 2. Late prenatal ducks kept the MO2 above the Arrhenius value at 28 degrees C, while the MO2 of pigeon hatchlings became the same as the Arrhenius value even at 32 degrees C. 3. Thus, incipient homeothermic ability appears in the duck during prenatal development, but it is not evident in the pigeon even after emergence from the shell. The precocial chicken and semi-precocial noddy previously studied are intermediate in their metabolic response between the duck and the pigeon.

Oxygen consumption of brown noddy (Anous stolidus) embryos in a quasiequilibrium state at lowered ambient temperatures

1. The oxygen consumption (MO2) of the semi-precocial Brown Noddy embryos at different stages of development was measured at 36 degrees C and again after 5-hr exposure to lowered ambient temperatures (30 and 32 degrees C). 2. The MO2 measured in a quasiequilibrium state was equal to the value predicted by a temperature coefficient of 2. 3. In contrast to precocial chickens, the semi-precocial Noddy had no apparent metabolic response to cooling before hatching.

Pre-pipping water loss from the eggs of the wedge-tailed shearwater

Abstract 1. 1. The water loss from naturally incubated eggs of the Wedge-tailed Shearwater was measured, together with the water-vapor pressure of the incubated eggs micro-climate, the egg temperature, the water-vapor conductance of the shell and other characteristics of the shell. 2. 2. The mean daily water loss (.MH2O) from the eggs (154.6 mg/day) was only 49.8% of the value expected on the basis of the mass of the freshly-laid egg. The low value for MH2o was attributed largely to a low water-vapor conductance (GH2O) of the shell (56.9% of predictions). The low GH2O. in turn, was due to fewer pores in the shell. 3. 3. Egg temperature (35.0 C) was lower than that of the eggs of birds in general, and this was considered to be a contributory factor to the low daily water loss. 4. 4. The water-vapor pressure (PH2Onest) of the eggs microclimate (19.57 torr) was similar to that of many surface-nesting birds in spite of the burrow-nesting habits of the shearwaters. 5. 5. It was calculated that the total pre-pippiny water loss from the eggs represented 12.2% of the initial mass of egg. 6. 6. It was concluded that prolonged incubation in the Wedge-tailed Shearwater, as in other smaller Procellariiformes. is associated with reduced values for .MH2O and GH2O and fewer pores in the shell.

Temperature regulation in a burrow-nesting tropical seabird, the Wedge-tailed Shearwater (Puffinus pacificus)

SummaryAt low air temperatures (2.3–13.9°C), Wedge-tailed Shearwaters (Puffinus pacificus) shivered and their oxygen consumption increased to as much as 283% of the mean value (0.77 ml O2/g·h) within the thermoneutral zone of air temperature (23–34°C). The minimal thermal conductance of the tissues and plumage was similar to the value predicted from the body mass (320.5 g). The oxygen consumption of the birds within their thermoneutral zone was lower than predictions based on body mass. At elevated air temperatures, the shearwaters panted at respiratory frequencies as high as 260 respirations/min; maximal respiratory frequencies were not invoked until the birds had become hyperthermic. During exposure to a hot environment, the oxygen consumption of the birds increased and in most instances the shearwaters were not able to lose heat equivalent to their concurrent metabolic heat production.

Water loss from the eggs of a tropical sea bird (Pterodroma phaeopygia) at high altitude

Abstract 1. 1. The water loss from the eggs of the dark-rumped petrel nesting at an altitude of 3000m in the Hawaiian Islands was studied. 2. 2. The conditions at the nest site were extremely dry and the calculated nest ventilation was very low (17.21/day). 3. 3. Comparisons with data from other Procellariiformes nesting at sea level suggested that the daily rate of water loss from the eggs of the dark-rumped petrel was high (134.5% of the predicted value for a procellariiform egg at sea level). 4. 4. The egg shells were thin and the shell mass was low—83.9% and 73.5%, respectively, of the values predicted for a procellariiform egg at sea level. 5. 5. It is believed that these features of the eggs are related to the altitude of the nesting site.

The emergence of endothermy in the black-footed and Laysan albatrosses

Eggs with pip-holes of the black-footed (Diomedea nigripes) and Laysan (Diomedea immutabilis) albatrosses were exposed to various air temperatures in the range 20–35°C in order to detect signs of incipient endothermy in late embryos. No evidence of endothermy was found. In contrast, the O2 consumption of most hatchlings increased in response to cooling, the O2 consumption at an air temperature of 25° C exceeding that between 34 and 35°C by 40%. In a minority of hatchlings this response was not seen. It was suggested that endothermy may develop at some time during the 24 h after hatching.