魚界女人國 七萬年沒演化
同樣跟女人國傳說一樣，「亞馬遜茉莉」都是找外族公魚交配。由於他們會自然篩選掉生公魚的DNA，所以，只有母魚會生下來。原來亞馬遜帆魚將在南德州時，是與扁鰭
花魚將(Poecilia latipinna)比鄰而居；而在北墨西哥的水域時，又與黑
摩麗魚(Poecilia sphenops, Molliensia sphenopsvar)同居。
這時扁鰭花魚將或黑摩麗魚的男士就會在晚上，跑到亞瑪遜帆魚將的
房間「過夜」。換言之，前二者之雄魚與帆魚將雌魚交媾，行體內受精。
但，奇妙的是，他們的愛情結晶卻不是「雜交種」。「女英雄」只借用這
外來的精子活化自己的卵子之細胞分裂，進而變成胚胎而已。換句話說，
帆魚將的下一代之遺傳因子（染色體），完完全全由媽媽那邊發展出來的
。爸爸的「遺傳」則與自己絕緣。這種繁殖方式，就叫作「雌性單性生殖
「亞馬遜茉莉」是生活在美國德州和墨西哥的魚類，英國愛丁堡大學的研究人員長期研究此物種，發現牠們是以跟「其他物種」的雄性作某種互動(interaction)來刺激其雌性個體本身的繁殖(reproduction process)，而生出來的下一帶基本上是母體的複製個體，而且並沒有遺傳任何雄性基因 ( The offspring are clones of their mother and do not inherit any of the male's DNA )，可以說是無性生殖。
無性生殖在物競天擇的演化論中對任何一個物種來說都是很危險的，很容易就面臨絕種的危機，研究人員用程式來推算，「亞馬遜茉莉」在過去70000年間就應該絕種了，但現在竟然還活得好好的，想必有某種遺傳上的「機制」(tricks)。
可是到底是什麼原因使「亞馬遜茉莉」還活到現在，研究人員還只在推論階段，他們目前推論：
或許「亞馬遜茉莉」偶而(ocassionally)會跟其他物種發生性行為；或許「亞馬遜茉莉」偶而會從其他物種身上弄些新的基因過來以更新(refresh)他們自己的基因庫(gene pool)。
研究人員猜想這種機制有可能也發生在其他物種身上，所以他們還要做更深入的研究。同時這項研究的報告已經發表在BMC Evolutionary Biology期刊雜誌上。
因為科學家早就知道這個基因會危害到「亞馬遜茉莉」的族群數量，但沒有人知道「到底多麼危害」。所以研究人員運用各項電腦程式模擬並計算，想要得到一個有數字的結果，那結果就是上面說的，牠們早該死光了。
結論就是「牠們怎麼還活著呢？」然後才出現你現在看到的這則新聞。
愛丁堡大學研究人員指出野外的「亞馬遜茉莉」需要藉由雄性精子來觸發(trigger，也就是我上面說的刺激啦 )牠們的繁殖，但在實驗室裡，研究人員用一根針就可以做到這樣的觸發，精子的作用是物理上的觸發，沒有基因上的貢獻，所以雄性DNA在此物種的繁演中不是必要的。
再說一點，「亞馬遜茉莉」的雌性個體產生卵子，我們都知道一般配子中的染色體是單套，但「亞馬遜茉莉」所產生的卵子已擁有雙套染色體，所以雖然說野生雌性個體「看起來」有與雄性個體交配的動作，但並沒有受精的事實，只是在雌體內實行上面所說的機制，所以整個繁殖不需要雄性染色體的參與。
No sex for all-girl fish species | |
A fish species, which is all female, has survived for 70,000 years without reproducing sexually, experts believe. Scientists from the University of Edinburgh think the Amazon Molly may be employing special genetic survival "tricks" to avoid becoming extinct. The species, found in Texas and Mexico, interacts with males of other species to trigger its reproduction process. The offspring are clones of their mother and do not inherit any of the male's DNA. Typically, when creatures reproduce asexually, harmful changes creep into their genes over many generations. The species will eventually have problems reproducing and can often fall victim to extinction. Scientists at Edinburgh University have been studying complex mathematical models on a highly powerful computing system to look at the case of the Amazon Molly. Researchers calculated the time to extinction for the fish based on modelling genetic changes over many thousands of generations. They are now able to say conclusively, for the first time, the fish ought to have become extinct within the past 70,000 years, based on the current simple models. Scientists believe the fish, which are still thriving in rivers in south-east Texas and north-east Mexico, are using special genetic survival "tricks" to help them stay alive. One theory is that the fish may occasionally be taking some of the DNA from the males that trigger reproduction, in order to refresh their gene pool. Species tricks Dr Laurence Loewe, of the university's School of Biological Sciences, said: "What we have shown now is that this fish really has something special going on and that some special tricks exist to help this fish survive. "Maybe there is still occasional sex with strangers that keeps the species alive. Future research may give us some answers." He added that their findings could also help them understand more about how other creatures operate. "I think one of the interesting things is that we are learning more about how other species might use these tricks as well," he said. "It might have a more general importance." The Edinburgh-led study was carried out in collaboration with Dr Dunja Lamatsch at the University of Wuerzburg, now at the Austrian Academy of Sciences. The research is published in the journal BMC Evolutionary Biology. | |
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