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First published online February 15, 2006
Journal of Experimental Biology 209, 834-844 (2006)
Published by The Company of Biologists 2006
doi: 10.1242/jeb.02057

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Cardiovascular and behavioural changes during water absorption in toads, Bufo alvarius and Bufo marinus

Arne L. Viborg^1,*, Tobias Wang² and Stanley D. Hillyard³

¹ Zoophysiological Laboratory, August Krogh Institute, University of Copenhagen, Denmark
² Department of Zoophysiology, University of Aarhus, Denmark
³ School of Dental Medicine and Department of Biological Sciences, University of Nevada, Las Vegas, USA

View larger version (14K): [in a new window]   Fig. 1 (A) Trace from the flow cytometer showing the increase in seat patch BCF of a B. alvarius dehydrated by 9.2% and placed on DI at time 0. (B) Mean seat patch BCF values ± s.e.m. from 15 trials (three replicates in five toads) with dehydrated B. alvarius; open symbols, BCF in the dry chamber; filled symbols, BCF on DI. (C) Effect of handling on BCF. Open symbol, BCF prior to handling; repositioning the toads on the probe caused a rapid decline in BCF, when the toads were left undisturbed BCF increased to the prehandling level within 3 min (filled symbols). The increase in BCF by dehydrated toads with 50 mmol l–1 NaCl in the reservoir was not different from that in A and B. P, pre-handling level.

View larger version (15K): [in a new window]   Fig. 2. (A) A trace from the flow cytometer showing the increase in seat patch BCF of a dehydrated (14.1%) B. marinus placed on water at time 0. (B) Mean seat patch BCF values ± 1 s.e.m. from 15 trials (three replicates in five toads) in dehydrated B. marinus; open symbols, BCF in the dry chamber; filled symbols, BCF on water. On water, BCF was significantly lower in B. marinus compared to B. alvarius (P<0.001, Fig. 1B vs Fig. 2B). Values for toads with 50 mmol l–1 NaCl were not different from DI.

View larger version (33K): [in a new window]   Fig. 3. Seat patch and fully immersed water uptake from DI water or NaCl (50 mol l–1) in B. alvarius (A) and B. marinus (B). Each column represents mean ± 1 s.e.m. for 15 trials, except seat patch water uptake from NaCl (12 trials). Regional water uptake read from the pipette or determined gravimetrically (broken lines) were not different. Regional seat patch water uptake was significantly lower from NaCl (**P<0.01). In contrast, full immersion resulted in significantly higher water uptake from NaCl (B. alvarius, *P<0.05; B. marinus, ***P<0.001). There were no differences between B. marinus and B. alvarius in water absorption from a given rehydration source.

View larger version (13K): [in a new window]   Fig. 4. Seat patch water uptake read from the pipette in B. alvarius placed on DI water (A) or NaCl (50 mol l–1) (B) plotted as a function of seat patch BCF during the same period. In A, 15 trials were performed and in B, only 10 trials as two of the toads often left the chamber within 10–15 min. Each point represents from 8–20 simultaneous measurements ± s.e.m. There was no correlation between BCF and water uptake from either DI or NaCl. Similar results were obtained with B. marinus.

View larger version (34K): [in a new window]   Fig. 5. Rates of water uptake in B. alvarius (A) or B. marinus (B) immersed in 1.5 mm, 6 mm or fully immersed in DI water or NaCl (50 mol l–1). Each column represents mean ± 1 s.e.m. for 15 trials. Water uptake from DI was not different irrespective of immersion level. In NaCl, increased immersion resulted in significantly increased rates of water uptake. **P<0.01; ***P<0.001.

View larger version (33K): [in a new window]   Fig. 6. (A) Water uptake in B. marinus fully immersed in DI water or NaCl (50 mol l–1), with or without the seat patch and the skin on the lateral sides covered by a mixture of beeswax and vegetable oil. Each column represents mean ± 1 s.e.m. of 15 trials. Water uptake from both DI and NaCl was significantly reduced when the skin was covered by the hydrophobic mixture. (B) Water uptake from DI or NaCl, with or without the skin on the lateral sides covered by the hydrophobic mixture. Water uptake from DI was not affected, but water uptake from NaCl was significantly reduced when the lateral skin was covered by the hydrophobic mixture. ***P<0.001.

View larger version (17K): [in a new window]   Fig. 7. BCF in toads in the dry chamber (filled columns) and in the wet chamber (open columns). Each column represents mean ± 1 s.e.m. of 15 trials. (A) In B. alvarius BCF did not increase when toads with ad libitum bladder water were placed on water (group A). Removing the bladder depot resulted in a significant stimulation of BCF in the wet chamber (group B). Mild dehydration resulted in a similar increase in BCF following water contact (group C). Dehydration (mean 15%) caused a further increase in BCF (group D). (B) B. marinus voided their bladders so ad libitum bladder measurements could not be obtained. Empty bladder B. marinus did not increase BCF when placed in on water (group B). Mild dehydration produced a small but significant increase in BCF (group C). Dehydration (16.9%) caused a further significant increase in BCF on water (group D). On dry substrate BCF did not increase significantly with dehydration in any of the species. **P<0.01; ***P<0.001.

View larger version (28K): [in a new window]   Fig. 8. (A) Representative traces from simultaneous recordings of central arterial flow (CAF, upper trace) and blood cell flux (BCF, lower trace) in a B. marinus dehydrated by 14.4%. (B) Time course for changes in CAF (filled circles) and seat patch BCF (filled squares). Each point represents mean ± 1 s.e.m. of nine trials in five toads. Recordings were started immediately after the toads had been transferred from the dehydration chamber to the wet chamber. CAF and heart rate (stars) declined during the first 3 min of recording, followed by an increase to a stable level, which was reached in 10 min. Initial CAF was much lower in two toads (four recordings, open circle), which remained unhandled in the dehydration chamber prior to water contact. (C) Time course for CAF and fH when dehydrated toads were presented with water but not handled. Because of the small sample size, data points are normalized as the ratio between the control values and those recorded sequentially after water exposure was initiated.