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Vol. 38 No. 1, 1999
Specific Gravity and Mechanisms for Its Control in Tadpoles of Three Anuran Species from Different Water Strata
Ming-Chung Tu*, Chia-Wei Chu and Kuang-Yang Lue
Department of Biology, National Taiwan Normal University, Taipei, Taiwan 116
Ming-Chung Tu, Chia-Wei Chu and Kuang-Yang Lue (1999)
Buoyancy regulation is crucial for the survival of aquatic animals
because it can save appreciable energy. Although anuran larvae are
generally benthic, a few species live either at the surface or in
mid-water. We have predicted that the specific gravity (sp. gr.) of
tadpoles in surface layers should be 1.0 or slightly less, and that of
midlevel tadpoles should be 1.0, whereas the sp. gr. of benthic
tadpoles should be greater than 1.0. We tested this prediction in tests
using larvae of Microhyla heymonsi, M. ornata, and Rana kuhlii
as representatives of surface, mid-waters, and benthic tadpoles,
respectively. Mean larval sp. grs. were 0.993 for M. heymonsi, 0.998
for M. ornata, and 1.041 for R. kuhlii.
Although the mean sp. gr. (x = 0.998) of mid-level tadpoles partially
contradicts our prediction (1.0), larval sp. grs. of the other 2
species did fit our prediction. The general trend for benthic tadpoles
to have a greater sp. gr. than those of mid-layer or surface tadpoles
was supported by our experiments. Lungs seem to play an important role
in buoyancy regulation for anuran larvae. To check this prediction, we
measured and compared sp. grs. of the same individuals with and without
lungs. Also, observations were made on larvae of surface and mid-water
species after being forcibly kept from contacting surface air. Results
of these experiments confirmed the importance of lungs in buoyancy
regulation in both M. heymonsi and M. ornata tadpoles. The larvae of M. heymonsi recovered from the deprivation of surface air treatment much better than did those of M. ornata. This phenomenon might be correlated with their different habitats.
Key words: Buoyancy, Anuran larvae, Amphibian.
*Correspondence: Tel: 886-2-29336875 ext. 321. Fax: 886-2-29312904. E-mail: Biofv026@scc.ntnu.edu.tw
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