Specific Gravity and Mechanisms for Its Control in Tadpoles of Three Anuran Species from Different Water Strata

蝌蚪比重與生活水層關係之研究

杜銘章(Ming-Chung Tu) ； 朱家蔚(Chia-Wei Chu) ； 呂光洋(Kuang-Yang Lue)

《Zoological Studies》 38卷1期 (1999/01) Pp. 76-81

摘要

對於水裡生活的動物而言，浮力調整得當，可以節省許多能量，因此身體比重的調節，直接關係著其生存適應的問題，雖然多數的蝌蚪屬於底棲型，多半時間生活在水塘的底部，但有些種類的蝌蚪，如小雨蛙(Microhyla ornata)，卻一直保持在水層中間，而黑蒙西氏小雨蛙(M.heymonsi)的蝌蚪，則多半懸浮在水表面下。我們推測上層型的蝌蚪，其比重應為1.0或比1.0梢小，而中層型的蝌蚪，其比重應為1.0，底棲型的蝌蚪，比重 則應大於1.0。我們以黑蒙西氏小雨蛙、小雨蛙和古氏赤蛙(Rana kuhlii)的蝌蚪，分別代表上、中和底層的蝌蚪，結果發現其比重分別是0.993、0.998和1.041，此和我們的預期 相當吻合，而且在摘肺後測量其比重，以及在防止上層和中層蝌蚪取得水面上的空氣試驗下，結果都顯示肺對於黑蒙西氏小而蛙和小雨蛙蝌蚪的浮力調整相當重要，不過此兩種蝌 蚪在無法吸取水面上的空氣達一週後，讓牠們再度接觸空氣，發現黑蒙西氏小雨蛙復原情 形較小雨蛙為佳，此現象可能和牠們棲地環境的不同有關。

關鍵字

浮力 ； 蝌蚪 ； 兩生類

並列摘要

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. omata, 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. omata, 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.

並列關鍵字

Buoyancy ； Anuran larvae ； Amphibian