以放射線學及超音波影像學觀察雌性食蛇龜生殖週期之變化

Abstract

食蛇龜屬於龜鱉目（Testudines）地龜科 (GeoGeoemydidae)，於野生動物保育法歸屬於珍貴稀有保育類野生動物，為了解其完整的繁殖週期，以期對淡水龜保育提供幫助。本研究以超音波及放射線來觀察紀錄圈養食蛇龜的繁殖週期，其中放射線可提供產蛋數的正確判斷，而超音波可以觀察記錄濾泡週期性變化，結合此兩種方式將更清楚了解食蛇龜的完整繁殖週期。 動物來源為台北市立動物園野生動物收容中心的24隻雌性食蛇龜，研究結果歸納，該族群平均背甲長為16.62 ± 1.66 cm，平均體重為812 ± 164.98 g，個體的年平均產蛋組為1.2窩，族群總產蛋窩數為29窩，族群總產蛋數合計為87顆，每窩平均為3顆蛋；於觀察期間，該族群繁殖頻度達98.53%。而該族群中擁有兩個產蛋組的個體數為5隻，而擁有單一產蛋組的個體為19隻，且兩個產蛋組的個體的平均體重與背甲長(814.35 ± 21.18g，17.32 ± 1.19cm )都大於單一產蛋組的個體(776.9 ± 24.29g，16.45 ± 1.69cm)，但統計上兩組的相關變異因子，如體重、背甲長、月均溫與平均濾泡大小則無顯著差異性。 觀察期為2007年4月開始持續觀察一年，每月進行2次超音波探測，由觀察結果得知，濾泡於10月份為最小值1.54 ± 0.26 cm，稱之潛伏期，然後於11月漸漸開始成長，於5月份達最大值為2.26 ± 0.27 cm，即為排卵之前的大小，4月中至6月，初該族群陸續排卵，6月至9月陸續產蛋，如此循環形成食蛇龜的完整生殖週期。統計分析結果，時間對濾泡大小有相當顯著的相關性(P<0.001)，亦即證明測量濾泡大小可以相對應於該個體所處在的生殖週期，這項關係可以幫助將來應用此實驗模式在野外調查上的信賴度。 於排卵期利用X-ray及超音波進行每日密集觀察以獲得濾泡如何排入輸卵管的影像，及觀察卵於輸卵管形成的過程。在超音波的觀察中，排卵將於一至二天內完成；排卵後第三天可開始看見薄層蛋殼影像，而後鈣質漸漸沉積，蛋內容物在排卵後兩週後開始漸漸模糊，到排卵第三週後即看不見卵黃構造。依據X-ray觀測，排卵後第八到九天可視蛋殼影像，蛋殼密度隨時間漸漸增大，在放射線下的影像也將越來越明顯。 本研究綜合以上的結果，得知食蛇龜在生殖週期內的各項變化，並將結果統計分析建立相關參考數值及影像，不但可作為將來復育計畫的參考及生殖系統疾病的診斷，並提供食蛇龜完整的生殖週期做為繁殖復育的依據，並建立一套淡水龜繁殖週期研究的模式，應用在其他保育物種。

Yellow-margined box turtle (Cuora flavomarginata) is list as endangered species in CITES appendix Π, however, understanding and research of reproduction of this species is extremely limited. In order to study its reproductive physiology, we combined radiology and ultrasound to observe the reproductive cycle of 24 female captive yellow-margined box turtles in Taiwan. Radiology was mainly to monitor clutch size, while ultrasound was to detect changing of follicles through the year. The observation of total 24 female turtles began from April 2007 to June 2008 and their average carapaces length (CL) was 16.62 ± 1.66 cm and average body weight (BW) was 812 ± 164.98 g. In total one year observation, their mean clutch size was 3 (87 eggs/ 29 clutches) and the reproductive frequency was 95.83% (23/24). We found there were 20.8% turtles with double clutches and 79.2% with single clutch in this population. There was no statistical significance of the clutch size to the BW and to the CL. In ultrasound, the ovulation occurred from March through August and the average follicular diameter was 2.16 ± 0.18 cm. The follicles came into latent period in October (1.54 ± 0.26 cm) and the vitellogenesis of the next reproductive cycle began in November. In radiology, the egg shell was able to be detected at the 9th day after the ovulation. Compared to ultrasound observation, the egg formation was detected 8-9 days later by radiology. Also we discovered the average period of oviductal eggs was 6.9 weeks. In conclusion, it is clearly that our study has shown a progress to realize the reproductive physiology of yellow-margined box turtle and has established a valuable and practical model for comparative study in reproductive physiology of other chelonians.