三種闊尾海蛇滲透壓調節能力之比較研究

Comparison of the osmoregulatory capability among three sea snakes (Laticauda spp.)

鄭元誠(Yuan-Cheng Cheng)

指導教授 ： 杜銘章 ； 林豊益

國立臺灣師範大學/理學院/生命科學研究所/碩士(2011年)

摘要

滲透壓與離子的調節與恆定是海洋脊椎動物面臨的生存挑戰之一，而個體的滲透壓調節能力往往與其海棲程度有相關性。海蛇的後端舌下腺(posterior sublingual gland)為其鹽腺，能夠排出濃縮的氯化鈉以維持滲透壓的恆定。鹽腺管狀構造之上皮由主細胞(principal cell)構成。主細胞底側膜上Na+/K+ -ATPase (NKA)以耗能的主動運輸將體內過多的鹽分排除體外。三種不同海棲程度的闊尾海蛇(Laticauda spp.)分布於台灣的蘭嶼及綠島；闊帶青斑海蛇(L. semifasciata)是海棲程度最高的物種，黑唇青斑海蛇(L. laticaudata)次之，而黃唇青斑海(L. colubrina)蛇是最陸棲的物種。本實驗目的為比較台灣三種闊尾海蛇的滲透壓調節力是否有所差異並呼應其海棲程度。將三種闊尾海蛇分別從陸域轉移至海水及淡水馴養，分析轉移後的第0, 2, 7, 14天的血漿滲透壓、血漿離子濃度、血球容積比、肌肉含水量以及鹽腺和腎臟的NKA活性變化，用這些指標來分析其滲透壓調節能力。結果顯示，相較於黑唇及黃唇青斑海蛇，海棲程度最高的闊帶青斑海蛇維持體液滲透壓、鈉氯離子濃度以及肌肉含水量最為穩定。闊帶青斑海蛇及黑唇青斑海蛇的鹽腺NKA活性在海水馴養組皆顯著高於淡水馴養組，而陸棲程度最高的黃唇青斑海蛇的鹽腺NKA活性不論轉移至海水或淡水都沒有顯著變化。以上證據顯示闊帶青斑海蛇的滲透壓調節能力較黑唇青斑海蛇及黃唇青斑海蛇佳。而最陸棲的黃唇青斑海蛇似乎採取不同於闊帶與黑唇青斑海蛇的滲透壓調節策略因應環境鹽度變化。

關鍵字

闊尾海蛇 ； 鹽腺 ； 滲透壓調節 ； 鈉鉀幫浦

並列摘要

Marine invasions have occurred multiple times independently among vertebrates. To permit the successful habitation of marine environments, the specialized ionoregulatory tissues have evolved, likely been responsible for ameliorating ionic challenge. Therefore, salt gland has evolved multiple times throughout the evolution of marine vertebrates. The sublingual salt gland is the primary organ of salt excretion in sea snakes, and Na+/K+–ATPase (NKA) in the basolateral membrane provides the driving force for salt secretion. In this study, the osmoregulatory capability of three sea kraits (Laticauda spp.) in Taiwan were examined and compared to test if their osmoregulatory capability is associated with their different habitats affinity from terrestrial to marine. The sea kraits were transferred from terrestrial environment to freshwater (FW) or seawater (SW) for 0, 2, 7, and 14 days. At various time points, their salt glands and kidneys were sampled for NKA activity analysis; muscles were sampled for water content measurement; blood were sampled for the analysis of hematocrit, osmolality, and ionic concentrations. Results showed that the most marine species, L. semifasciata maintained better constancy in plasma osmolality, Na+, Cl- levels and water content. In L. semifasciata and L. laticaudata, the NKA activity of the salt gland was higher in SW than in FW. However, in the most terrestrial species, L. colubrina, no significant difference of NKA activity was found between SW and FW groups. These results suggest that the capability of osmoregulation is better in L. semifasciata than in the other two species, and L. colubrina may have different osmoregulatory strategy with the other two species.

並列關鍵字

sea krait ； salt gland ； osmoregulation ； Na+ /K+ -ATPase

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