Physiological Zero Research Articles

Energetics of Incubation in Free-Living Orange-Breasted Sunbirds in South Africa

Using the single-sample variant of the doubly labeled water method (DLW), I quantified the field metabolic rate (FMR) and water flux of female Orange-breasted Sunbirds (Nectarinia violacea) during the incubation period. Concurrent to DLW measurements, I examined their incubation behavior and microclimate. These are the first measurements of FMR and water flux for a nectarivorous bird during incubation and the first for an Old World sunbird species. For 10 incubating female Orange-breasted Sunbirds (mean mass = 9.5 g), CO2 production averaged 13.3 ml/hr, which corresponds to a FMR of 66.2 kJ/day, one of the highest values reported for a bird of its size. Among female passerines, the ratio of FMR to basal metabolic rate (BMR) is typically near 3.0, but for female Orange-breasted Sunbirds, the ratio of FMR/BMR is near 6.5. This suggests that during incubation females are working near their maximum capacity. Females generally lost mass during experimental periods; birds with high mass loss have elevated FMRs. Females consumed 14.7 ml H2O/day, slightly more than twice that expected based on body size. Attentiveness of females averaged 39.4 min/hr, while incubation bouts and inattentive periods averaged 11.9 min and 6.7 min, respectively. Females stayed away from their nests for long periods in the late afternoon, especially during inclement weather. Egg temperature averaged 34.7°C for all experimental periods combined. When females were absent for extended periods, eggs cooled to ambient temperatures, often near 10°C. This is a temperature well below the physiological zero temperature. The FMR of females increased significantly with decreasing operative temperature. One observation suggested that when in negative energy balance, females lower their body temperature while on the nest at night. These are the first data suggesting that sunbirds use hypothermia as an energy conservation mechanism in the field.

Research Note: Variability in Preincubation Embryonic Development in Domestic Fowl.: 2. Effects of Duration of Egg Storage Period

Embryos of eggs from Single Comb White Leghorn hens were analyzed to determine whether duration of egg storage significantly affects embryonic development prior to incubation. Eggs were gathered over a period of 5 days from 25-wk-old hens that were naturally inseminated and housed in floor pens. Within 1 h of oviposition the eggs were collected and assigned randomly to one of five storage treatment groups of 0, 4, 7, 14, or 21 days. Fresh egg weight was recorded and the eggs were placed on plastic egg flats and stored at 14 C. Weight of each egg was measured after storage to determine amount of weight lost during storage.A total of 500 embryos were examined after storage. Viable embryos were staged for development using a modified Eyal-Giladi and Kochav classification. The incidence of embryonic mortality was noted. Duration of storage (P = .5815) collection date (P = .5815), and fresh egg weight (P = .3789) did not affect embryonic development significantly. A significant linear relationship was observed between duration of the storage period and loss of egg weight (P = .0001). Embryonic mortality was significantly related to loss of egg weight (P = .0001). Mortality was highest in eggs that were stored for a longer period of time. The data from the current study indicate that storing fertile eggs below physiological zero inhibits embryonic development. One of the reasons for the increased incidence of embryonic mortality in eggs that were stored for longer periods may be related to the increased egg weight loss in these eggs.

Incubating Female Passerines Do Not Let the Egg Temperature Fall below the 'Physiological Zero Temperature' during Their Absences from the Nest

Egg temperature was recorded at 1-5 min intervals during the incubation period in 42 nests of 14 different species. Only the females incubated. The egg temperature therefore declined whenever a female left the nest for a period-off. Regardless of the ambient temperature, however, the females usually returned to their nests and continued incubating before the eggs had cooled down to the suggested 'physiological zero temperature' (25-270C). For 14 nests (6 species) in which egg temperature was measured at 1 min intervals, the mean minimum egg temperature (MET) during periods-off was 30.4'C. The mean value for all 42 nests, with recording intervals varying from 1-5 min, was 31.20C. It is suggested that the incubation rhythm adopted is adaptive and evolutionary aspects of the high MET-values are tentatively discussed. During periods of especially low ambient temperature the female either holds the egg temperature at a normal level or temporarily stops incubating altogether. Any intermediate solution seems to be ruled out.

Thermal Tolerance of Avian Embryos: A Review

Avian eggs usually experience temperatures of 30 to 40°C during the incubation period, but eggs often cool to much lower temperatures. Hyperthermia is less common. Passerines do not show higher incubation temperatures than other orders that have been studied extensively. Field measurements of incubation temperatures are usually lower than the optimal temperatures for development found in laboratory studies. Some species regulate egg temperatures closely throughout incubation; but in at least one penguin species, mean egg temperature increases and ranges of egg temperature decrease through the incubation period. Both the optimal temperature for continuous exposure and the range of temperatures producing high survivorship differ among species. Species also differ in their responses to temperature exposures of limited duration. Thus, the use of a "physiological zero" applicable to all species is not warranted. Penguins have both a lower optimum and a broader range of acceptable incubation temperatures than do other species studied. Age, duration, and temperature of exposure significantly affect survivorship. Hyperthermia is evidently more injurious to the developing embryo than is hypothermia. Resistance to cold exposure is a heritable trait, but the genetics and physiology of the response(s) are not known. For older embryos, the physiological effects of hyperthermia are similar to those of adult birds in terms of the organ systems that are first to fail. An estimate of thermal tolerance for short exposures in most species studied is 16 to 41°C and, for exposures lasting several hours, 36 to 39°C.

Temperature sensitivity: One subjective continuum or two?

The full range of nonpainful temperatures (approximately odeg C to 52 deg C) was scaled by magnitude estimation with the standard at physiological zero (32 deg C). Apparent magnitude bore an exponential relationship to temperature over this range, although the same Os gave power functions when judging warmth or cold alone. A transformation is presented, which, when applied to the appropriate sections of the exponential relationship for the full range, produced functions indistinguishable from the power law for warm and cold ranges. The conclusion Stevens and Stevens (1960) drew from the results of scaling warmth and cold alone, namely that a ϕo threshold correction should be applied to the physical scale of all continua to derive power law functions from magnitude estimations, is shown to be an invalid generalization from temperature scaling.

Physiological zero and the psychophysical law

Physiological zero and the psychophysical law

The Effect of Age and Holding Temperatures on Hatchability of Turkey and Chicken Eggs

THE embryo of the hen at the time the egg is discharged from the oviduct has, according to Patton (1929) and others, reached approximately the gastrula stage. This period of development is marked by the formation of the gastrocoele (primitive gut) in which the cells of the blastoderm have invaginated into the segmentation cavity. Future development from this point is dependent on temperature. A cessation in development occurs when the embryo is held below physiological zero, 20°C. to 21°C. (68°F. to 69.8°F.). The question of how long fertile eggs may be held before setting and yet be capable of developing into normal chicks has been investigated by a number of workers.Broca (1862) as quoted by Lippincott (1927) observed that blastoderms 27 days of age at time of setting frequently developed for a short period and then died. Lippincott (loc. cit.) quotes Lavison (1862) as having obtained a few normal .

THE PHYSIOLOGICAL ZERO: AN EXPLANATION OF THE DEPARTURE FROM THE LINEAR GRAPH OF REACTION RATE VALUES AT THE LOWER TEMPERATURES

Considerable controversy has arisen between investigators de, l~ng with the influence of temperature upon physiological reaction rates. Some reactions are decidedly exponential, others clearly linear functions of the temperature. To the first class belong the results of Snyder (I913), on the rate of beat of the mammalian heart and those of Loeb and Northrop (1917) on the length of life of Drosophila. The work of Sanderson (1910), Peairs (1914) and others on insect development and that of Krogh (1914) on general metabolism estab. lish the latter relationships. Marked deviations from the linear curves have been noted at the upper and lower temperatures, making necessary the qualifying clause that the linear relations only held between the normal limits of growth. The departures at the upper temperatures have received an explanation. It is generally conceded that the linear is a modified exponential whose secondary factor increases more rapidly than the primary one at the higher temperatures. The departures at the lower temperatures have only been noted in connection with methods for the calculation of the physiological zero. Thus if we were to apply Pealrs' method for the determination of the physiological zero to the development of Drosophila melanogaster it would come at about 8°C. in the work of Loeb and Northrop (1917), and at 10°C. in my own experiments (Krafka (1919-20)).