Effects of hypoxia on egg capsule conductance in Ambystoma (Class Amphibia, Order Caudata).

Aquatic amphibian eggs frequently encounter hypoxic conditions that have the potential to limit oxygen uptake and thereby slow embryonic development and hatching. Oxygen limitation might be avoided if egg capsule surface area and oxygen conductance increased in response to hypoxia. We investigated this possibility in two salamander species, Ambystoma annulatum and Ambystoma talpoideum. The effective surface area of egg capsules increased in response to hypoxia, which increased the conductance for oxygen and enhanced oxygen transport. The ability of amphibian eggs to adjust their conductance in response to oxygen availability may increase survival in hypoxic environments.

Effects of hypoxia on embryonic development in two Ambystoma and two Rana species.

Oxygen available to amphibian embryos fluctuates widely and is often very low. We investigated the effects of oxygen partial pressure (1. 3-16.9 kPa) on embryonic development and hatching of two salamander (Ambystoma) and two frog (Rana) species. In Ambystoma, chronic hypoxia resulted in slowed development, delayed hatching, and embryos that were less developed at the time of hatching. Although hypoxia was not lethal to embryos, temporary developmental abnormalities were observed in Ambystoma at oxygen partial pressures of 3.8 kPa and below. Posthatching survival decreased below 3.3 kPa. In Rana, hypoxia did not affect developmental rate, presumably because hatching occurs at a very early stage of development relative to Ambystoma. However, Rana embryos hatched sooner in hypoxia than in normoxia, resulting in less developed embryos at the time of hatching. The results suggest that embryonic hypoxia may negatively affect survival and fitness in these species.

Evaporation from reusable cloth diapers exposed to radiant heat.

This study determined the rate of evaporation from four sets of diapers: disposable diapers with and without a heat shield, and cloth diapers with and without a heat shield. The evaporation was greatest from the cloth diaper without the heat shield (51% after 1 hour, 81% after 2 hours) and the least from the disposable diaper covered by a heat shield (15% after 1 hour, 30% after 2 hours). We recommend that if cloth diapers are used to monitor urine output from sick neonates that (1) the diaper should be weighed promptly after urination with accurate and precise scales, and (2) a heat shield should cover the diaper.

Micromethod for dynamic determination of O2 dissociation curves using a PO2 electrode.

A nonspectrophotometric method is described for measurement of the O2 dissociation curve and O2 capacity of a 50-microliter sample of fluid. PO2 is recorded by a microprocessor as the sample is oxygenated and then deoxygenated by exposure to isocapnic gas mixtures across a gas-permeable membrane. The time course of deoxygenation and the O2 conductance of the membrane are used in calculating the O2 capacity of the sample and the dissociation curve. The method is sensitive and is best suited to samples of low O2 capacity and affinity. Measurements on buffer-diluted human blood agree with standard values.

Varied egg gas conductance, air cell gas tensions and development in Agapornis roseicollis.

Different color varieties of the small African parrot, Agapornis roseicollis , lay eggs which differ by as much as a factor of 7 in gas conductance. Oxygen consumption (VO2) and air cell gas tensions (PAO2, PACO2) were measured repeatedly on individual eggs during development. No differences were observed in the ontogeny of VO2, incubation period, or hatchling mass of eggs with different gas conductances, in spite of large differences in PAO2 and PACO2. Low conductance eggs reached PAO2 as low as 46.0 torr (6.13 kPa) and PACO2 as high as 90.5 torr (12.07 kPa). Although pipping occurred earlier in low conductance eggs, pipping did not occur at similar air cell gas tensions in eggs differing in conductance. Chorioallantoic membrane development was about 75% complete on day 12 and not fully complete until day 18 of the 22-23 day incubation period. The capacity of avian embryos to develop and hatch normally in eggs of different conductances may be important in allowing adaptation to varying nesting environments.

Respiratory gas exchange during thermogenesis inPhilodendron selloum Koch.

During peak thermogenesis of anthesis, high rates of respiration by the sterile male florets on the spadix ofPhilodendron selloum significantly reduce the oxygen tension (PO 2) and raise CO2 tension between the florets. Nevertheless, respiration is not limited by the availability of O2 under natural conditions. At experimental PO 2 below about 17 kPa, however, florets begin to show decreased O2 consumption. A respiratory exchange ratio of 0.83 indicates that the major energy source is not starch, but is probably lipid.

Respiration and heat production by the inflorescence of Philodendron selloum Koch.

During a 2-d sequence of anthesis, the spadices of the thermogenic arum lily, Philodendron selloum, regulated maximum temperature within a small range (37-44°C) by reversible thermal inhibition of respiratory heat production. This response protects the inflorescence and the attracted insects from thermal damage. Heat production by whole spadices, measured by O2 respirometry, equalled heat loss, measured by gradient layer calorimetry, which confirmed the heat equivalence of O2 consumption (20.4 J ml(-1)). This also indicated that there was no net phosphorylation during thermogenesis, heat production being the primary function of high rates of respiration. The sterile male florets consumed about 30 ml g(-1) h(-1) and the average 124-g spadix produced about 7 W to maintain a 30°C difference between spadix and ambient temperature. Most of the energy for thermogenesis is present in the florets before anthesis. Despite high respiratory rates, thermogenesis is an energetically inexpensive component of the reproductive process.