面天樹蛙卵粒的水分維持研究

Abstract

本實驗過程主要是在實驗室中控制不同環境條件，研究面天樹蛙 (Chirixalus idiootocus)卵粒如何適應陸地乾燥環境及其機制。 在本實驗中，以○1測試不同環境相對溼度下卵粒水分散失情形；○2測試失水的卵粒水分再吸收的速率；○3以不同失水程度的胚胎存活率，測試胚胎的耐旱性；○4比較卵鞘的有無對水分散失及胚胎耐旱性的影響；○5比較在同樣乾燥環境下，不同排列方式及不同基質含水量對卵粒水分散失的影響等方法研究面天樹蛙卵粒在水分維持及乾燥適應方面的能力。 實驗結果顯示：面天樹蛙卵粒與其他陸生兩生類卵粒一樣，對水分有極大通透性，且無法防止水分蒸散至空氣中。卵粒中大部分水分的蒸散，並不會影響到胚胎發育；且卵粒自周圍環境中吸水來補充水分能力很強。卵粒的卵鞘(capsule)在實驗結果顯示無法防止水分散失，但其可作為蓄水處所，使得卵粒水分蒸散時不容易影響胚胎發育。另外，胚胎發育快速(受精後約五天可發育成蝌蚪) 、胚胎耐旱性高(可忍受失水達總重80%以上) 等特徵，配合雌性親代在產卵時適當微棲地的選擇及特殊的築巢行為，使得面天樹蛙的卵粒能成功的適應台灣中低海拔(亞熱帶及溫帶)的氣候而在陸地上普遍繁殖後代。The endemic tree frogs Chirixalus idiootocus lay their eggs in rather moist environment on land. In the laboratory, we study the structure of the egg, the rate of dehydration and rehydration of the egg, the embryo tolerance of desiccation, the function of the egg capsule in water balance, and the influence of various sizes of egg mass and substrate moisture. The egg loses water freely by evaporation in various humidity conditions, the lost of water comes from the capsule and not from the embryo. The egg lost 80% hydrated weight water could recovery very quick to initial diameter after flooded within 15 minutes. The weight of hydrated eggs can be reduced by 80% to 90% without affecting embryo viability. Egg mass can reduce water loss and substrate moisture can be taken up water by eggs to resistant desiccation. The rate of development, structure of egg capsule, choice of oviposition site and form of egg mass are other important factors relevant to the terrestrial survival of embryo.