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SYNOPSIS. Profound developmental changes occur in the morphology and physiology of the respiratory system of amphibians during the transition from strictly aquatic to dual aquatic-aerial breathing. This developmental transition usually involves modifications in ventilatory mechanisms and/or respiratory surfaces {e.g., degeneration of gills, ventilation of functional lungs). Both the first appearance of obligate air breathing and the subsequent dependence upon it by amphibian larvae are sensitive to a variety of environmental stressors during critical developmental periods. These stressors include oxygen availability, ambient temperature, the risk of predation and mode of feeding.

The neotropical frog Eleutherodactylus coqui (Thomas) undergoes direct development within the egg, emerging at hatching as a juvenile frog. The aim of this study was to investigate cardiorespiratory changes that accompany development, as well as to determine how the developmental physiology of direct-developing anurans differs from anurans with free-living larval stages. Heart rate (fH), oxygen uptake , vitelline fluid pH, and the protein and lactate concentrations of vitelline fluid were measured as a function of development. At 24–25 °C, fH doubled from 50 to 100 beats min−1 during the early stages of heart development, then increased more slowly with later embryonic development to 120 beats min−1 at hatching. The act of hatching itself was accompanied by a transient increase in fH to 155 beats min−1, this mild tachycardia lasting for at least 2 h. In juveniles and adults, heart rate decreased with increasing body mass, falling to about 80beats min−1 in 6 g frogs at 24–25°C. at 24–25 °C increased from about 2μmol g egg−1h−1 for the earliest embryos examined to about 12μmolg egg−1h−1 at hatching. in adults decreased with increasing body size, ranging from 4 to 5μmolg−1h−1 in the largest adults examined (6g). Both fH and were also measured at 18°C. The Q10 for/it was between 1.5 and 2 throughout development. The Q10 for in embryos ranged between 3.5 and 6.5 until hatching, falling to 1.6–2.0 in juveniles and small adults. Vitelline fluid pH (24–25°C) decreased from 5.2’ in early embryonic stages to 4.7 at the time of hatching. Egg dehydration caused a significant decrease in the pH of vitelline fluid and was associated with a significant rise in fH. Vitelline fluid protein concentration was about 5–6mgdl−1, and showed no consistent change with development. Whole-egg lactate concentration ranged from 4 to 11 μ g g egg−1, and also showed no consistent change during development. These findings indicate considerable changes in cardiac and metabolic physiology associated with opment in Eleutherodactylus coqui. These changes appear to be associated with both organogenesis (primary influence before hatching) and body mass changes (primary influence after hatching).

The CO2-specific sensitivity of hemocyanin oxygen affinity and oxygen binding site cooperativity were investigated in five species of crabs. The hypothesis that CO2-specific effects on hemocyanin are related to the molecular CO2 concentrations that occur naturally in crab hemolymph was tested in crabs that experience a variety of hemolymph CO2 pressures. Crab species were chosen from subtidal, intertidal, and semiterrestrial habitats. Hemolymph samples from each species were added to physiological salines buffered with 50 mM HEPES. O2 equilibrium curves were determined spectrophotometrically by gassing the hemolymph-saline mixtures with different P at constant P and temperature. We found no CO2-specific effects on oxygen equilibrium properties of hemocyanin in any species under the conditions investigated. It is concluded that molecular CO2 and bicarbonate ions are not important in directly modulating the oxygen equilibrium properties of crustacean hemocyanins.