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 (MOO2), 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−11, this mild tachycardia lasting for at least 2 h. In juveniles and adults, heart rate decreased with increasing body mass, falling to about 80 beats min−1 in 6 g frogs at 24–25°C. MOO2 at 24–25°C increased from about 2 μmol g egg−1 h−1 for the earliest embryos examined to about 12 μmol g egg−1 h−1 at hatching. MOO2 in adults decreased with increasing body size, ranging from 4 to 5 μmol g−1 h−1 in the largest adults examined (6 g). Both fH and MOO2 were also measured at 18°C. The Q10 for fH was between 1.5 and 2 throughout development. The Q10 for MOO2 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 5–6 mg dl−1, and showed no consistent change with development. Whole-egg lactate concentration ranged from 4 to 11 μg g egg−1, and also showed no consistent change during development. These findings indicate considerable changes in cardiac and metabolic physiology associated with development in Eleutherodactylus coqui. These changes appear to be associated with both organogenesis (primary influence before hatching) and body mass changes (primary influence after hatching).

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