The thermal environment of arboreal pools and its effects on the metabolism of the arboreal, oophagous tadpoles of a Taiwanese tree frog, Chirixalus eiffingeri (Anura: Rhacophoridae)

We have studied seasonal and diurnal fluctuations of water temperature in bamboo stumps and the effect of temperature on the energy metabolism of arboreal, oophagous tadpoles of Chirixalus eiffingeri. We collected tadpoles (Gosner stage 28-29) in February and August from Chitou, Taiwan and acclimated them to 12 and 22 degrees C. Using a closed system, we measured tadpole oxygen consumption (V.O(2)) at 12, 17 and 22 degrees C. The water temperature was lowest in February (11-13 degrees C), increased rapidly during March and April and was highest from May to August (20-24 degrees C). Diel fluctuations in the temperature of the pools of water in bamboo stumps mirrored fluctuations in air temperature. Tadpoles collected in February and August exhibited metabolic compensation in that tadpoles acclimated at 12 degrees C had significantly higher V.O(2) than those acclimated at 22 degrees C. There are at least two possible explanations for the presence of metabolic compensation in C. eiffingeri tadpoles. Firstly, the larval period of C. eiffingeri ranges from 40 to 78 days, a tadpole could experience relatively large fluctuations in body temperature (up to 10 degrees C) during the development. As a result, C. eiffingeri tadpoles most likely evolved metabolic compensation to maintain activity levels under different thermal environments. Secondly, because arboreal pools are small, thermally unstratified, aquatic microhabitats, tadpoles are unable to behaviorally select preferred temperatures. As a result, metabolic compensation allows tadpoles to regulate their physiological functions.

Water balance, growth, development, and survival of arboreal frog eggs (Chirixalus eiffingeri, Rhacophoridae): importance of egg distribution in bamboo stumps

We studied the effects of substrate moisture and flooding on the arboreal eggs of Chirixalus eiffingeri and determined the possible causes of egg mortality. Eggs appear highly permeable to water vapor, losing 16.24% and 38.38% of initial egg mass in 2 h at 90% and 45% relative humidity, respectively. Eggs that experienced positive water uptake developed faster, hatched earlier with larger hatchlings, and had greater hatching success than eggs that experienced negligible or negative water uptake. The hatching success of eggs that were submerged in water in bamboo stumps was significantly lower than that of eggs that were incubated on the water surface and was significantly correlated with the water PO2. In some bamboo stumps, we observed chironomid and tipulid larvae preying on submerged eggs. A dilution of water collected from bamboo stumps did not increase the hatching success of eggs. The water PO2 of bamboo stumps in the field was 67.4+/-18.8 mmHg, and the degree of hypoxia of water in each bamboo stump was correlated with the turbidity. Our findings demonstrated that the vertical distribution of C. eiffingeri eggs on walls of bamboo stumps significantly influenced the growth, development, and survival of embryos. Eggs deposited too far from the water may become desiccated, while eggs deposited too close to the water may become submerged and die of hypoxia or predation by insect larvae.

Physiological effects of hypoxia on metabolism and growth of turtle embryos

Hypoxic effects on embryonic metabolism and growth of Florida red-bellied turtle (Pseudemys nelsoni) embryos were studied. Eggs were assigned to either normoxic (21% O2) or hypoxic (10% O2) treatment on day 21. Oxygen consumption (VO2) and embryonic mass were measured periodically. On day 21 and 33, critical oxygen tension (Pc) of embryos and morphometry of blood vessels in chorioallantoic membranes were measured. Although embryos exposed to normoxia increased VO2 and mass at a rate greater than those in the hypoxic condition during incubation, both groups hatched at the same time. Hatchlings from the hypoxic treatment had elevated hematocrit and greater relative dry ventricular mass compared to hatchlings from the normoxic treatment. The Pc of hypoxic embryos was significantly lower than normoxic embryos on day 33 (P < 0.001). Morphometric comparison of blood vessels in chorioallantoic membranes revealed no significant differences except in length density on day 33 (P < 0.05). It is concluded that exposure to chronic hypoxia resulted in retarded growth, depressed metabolism, comparable incubation period, and reduced hatchling mass. In addition, embryos exhibited some physiological plasticity which allowed increased oxygen transport in response to hypoxia.