蛇類在適應不同生態環境的過程中，其形態、生理和行為上都表現出適合生存的特徵。已知樹棲蛇類的體型特別細長，血管肺較短，血壓偏高並有隨風搖擺的特殊行為。另外文獻雖認為樹棲蛇類跨越懸空的能力較強，但卻無數據加以支持。同樣的，雖有文獻的圖例顯示，樹棲蛇類的氣囊較陸棲蛇類長，但沒有其他文獻更進一步支持此現象。因此本研究旨在澄清樹棲蛇類的跨越能力是否較強，並探討蛇類的氣囊是否有助於其做跨越的動作。在檢視台灣地區的兩種黃頜蛇科蛇類﹕大頭蛇 (Boiga kraepelini) 和紅斑蛇(Dinodon rufozonatum)以及兩種蝮蛇科蛇類﹕赤尾青竹絲 (Trimeresurus stejnegri) 與龜殼花 (Trimeresurus mucrosquamatus) 的內臟器官相對於腹鱗的位置，和其所占腹鱗數的百分比。發現親緣關係是決定內部器官位置或比例長短的主要因素，而棲地類型則是次要導致親緣關係相近的蛇類在形態構造上的分化的次要因素。樹棲蛇類的呼吸道長度比例顯著大於陸棲性蛇類。
為了了解蛇類懸空的跨越能力是否因棲地而有不同，以台灣地區的三種樹棲型蛇類，分別為大頭蛇、台灣鈍頭蛇 (Pareas formosanus) 和赤尾青竹絲以及三種陸棲型蛇類，分別為紅斑蛇、龜殼花、眼鏡蛇(Naja atra)，作為測試的實驗材料。並以三種不同的方式表示其跨越能力，分別是(1)跨越距離除以吻肛長 (Csv)，(2)跨越距離除以全長 (CT) 和(3)跨越距離除以吻端至其重心點的距離 (CG) 。結果顯示三種不同的表示方式，都是樹棲蛇類跨越能力比陸棲蛇類好。
另一方面，在測試氣囊是否有助於蛇類做跨越動作的實驗部分，用馴養期間適應良好、數量最多的紅斑蛇作手術插管，並記錄肺內壓的變化。結果顯示，紅斑蛇在休息狀態下的呼吸頻率、平均肺內壓與平均肺內壓振幅都顯著小於活動狀態下的變化。在連續底質上的爬行與跨越時的肺內壓則無顯著差異，但是測試個體在跨越極限距離時會出現肺內壓的高峰。進一步以橡皮軟管 (外徑﹕0.55 cm，內徑﹕ 0.40 cm ) 插入部分個體的氣囊內，使其肺內壓力無法上升，但紅斑蛇仍能達到其原來的最大跨越極限，因此顯示氣囊對陸棲型的紅斑蛇沒有輔助跨越的功能。但是氣囊是否有助於樹棲型蛇類做跨越動作，則尚待進一步的實驗去驗證。

To adapt for arboreal life, tree-dwelling snakes have adopted many changes in morphology, physiology and behavior. Although arboreal snakes seems have better cantilever ability, this behavior has not been studies quantitatively. Similarly, their air sac was shown to be longer than that of terrestrial snakes in a figure of one paper. But, no other report has verified whether this is a general trend. Consequently, I tried to cheek if above two phenomena is true and inquire whether air sac possess a function of aiding snakes in spanning.
I examined the relative position of viscus to abdomen scales of 4 snakes: Boiga krapelini, Dinodon ruforzonatum, Trimeresurus stejnegeri and Trimeresurus mucrosqumatus. Phylogeny played more important role in shaping the position and length of viscus. However, within the same taxa, arboreal snakes did possess longer air sac than terrestrial snakes. To test whether arboreal snakes have better cantilever ability than terrestrial snakes, I added 2 more species; Pareas formosanus and Naja atra, in the cantilever experiments. All the arboreal snakes(B. krapelini, T. stejnegeri and Pareas formosanus )showed a better cantilever ability than terrestrial snakes(D. ruforzonatum, T. mucrosqumatus and N. atra) despite the difference of phylogeny.
I used only D. ruforzonatum to examine the role of air sac in cantilever behavior. Because this species adapted well in laboratory and was abundant in the field. To monitor the intrapulmonary pressure in the air sac, I implanted a tube in the air sac and connected it to a pulse transducer. In resting condition, the respiratory frequency, mean intrapulmonary pressure, and amplitude of pressure were all significantly larger than that when in moving on the ground or spanning gaps. Although intrapulmonary pressure increased clearly when a snake almost reached its maximal cantilever length, no statistical difference of respiratory frequency, mean intrapulmonary pressure, and amplitude of pressure was found between crawling and spanning condition. When I further deflated the intrapulmonary pressure by implanting another bigger rubber tube in the air sac, I found the snake could still span a same length as before. Therefore, the results did not support the idea that air sac may aid snakes to span gaps. Because D. rufozonatum is a terrestrial snake, further investigation will reveal whether this condition may also apply to arboreal snakes.

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