許多雄性動物有著極為誇張的性徵與繁殖行為,例如孔雀的華麗的飾羽或青蛙的洪亮的鳴叫聲等,在幾百年前即受到博物學家的關注(圖一)。這些用來吸引異性的特徵很明顯不利於個體生存,不太可能是天擇 (natural selection) 下的產物,達爾文提出天擇說時當然不會遺漏這些神奇的現象,他將其寫入在 1871 出版的《The Descent of Man, and Selection in Relation to Sex》中,這也是演化生物學中「性擇」研究的起點。
「她是那麼勇敢而美好。」[1]美國疾病管制與預防中心(Centers for Disease Control and Prevention)2023 年 9 月號的《新興傳染病》(Emerging Infectious Diseases)期刊,登載一則來自澳大利亞的個案。[1, 2]論文的通訊作者對媒體表示:「你不會想成為全世界第一個被蟒蛇蠕蟲感染的病患,我們向她脫帽致敬。」[1]
這隻蛻變到三齡階段,外表朱紅的幼蟲,有 3 片典型的蛔蟲科唇瓣和盲腸,但缺乏發育完全的生殖系統。牠的頭尾被剁下來,由 CSIRO 的澳洲國家野生收藏館(Australian National Wildlife Collection)保存;其他屍塊分別交給雪梨大學(University of Sydney)以及墨爾本大學(University of Melbourne)鑑定基因。果然該寄生蟲專家所言不假,真的是 Ophidascaris robertsi。[2]
Ophidascaris robertsi 生活史
Ophidascaris robertsi 這種澳洲原生的蠕蟲,採行所謂的間接生活史(indirect life cycle),一輩子寄生多個宿主:成蟲住在最終宿主(definitive hosts)地毯莫瑞蟒(Morelia spilota)的食道和胃裡,牠們的卵則會點綴於蛇糞之中。身為中間宿主(intermediate hosts)的小型哺乳類,特別是澳洲特產的有袋動物,糊里糊塗吃了卵,幼蟲便竄入牠們胸腔和腹腔內臟,活上很長的一段時間。直到有天,地毯莫瑞蟒獵捕小動物果腹,故事就再從頭來過,生生不息。[2]
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