據(jù)英國《每日郵報(bào)》報(bào)道,，一項(xiàng)新研究表明一種神奇魚類全是女兒身，7萬年來從未交媾,，但一直繁衍至今,，在公然挑戰(zhàn)達(dá)爾文的進(jìn)化論。這種魚就是亞馬遜帆鰭鱸（Molly）,。
英國科學(xué)家表示,，一般來說，有性物種若以無性繁殖,，過不了幾代就會出現(xiàn)基因殘障,，最后絕種。按理說亞馬遜帆鰭鱸應(yīng)該絕種,，但它們巧妙地利用遺傳基因來得以幸存,。
眾所周知，有雄魚精子才能形成胚胎,，但亞馬遜帆鰭鱸的所有后代似乎沒有爸爸的一點(diǎn)DNA,，而是全部繼承了媽媽的基因物質(zhì)。
但亞馬遜帆鰭鱸仍舊繁衍在美國德州東南部和墨西哥西北部的河流中,，這令科學(xué)家大為意外,。
為解開這一謎團(tuán)，英國愛丁堡大學(xué)的科學(xué)家通過高性能的計(jì)算機(jī)系統(tǒng)來研究復(fù)雜的數(shù)學(xué)模型,，以分析亞馬遜帆鰭鱸的這一特別案例,。根據(jù)模型計(jì)算亞馬遜帆鰭鱸數(shù)千代魚的基因變化情況，科學(xué)家得出它們應(yīng)該在7萬年前就滅絕了,。
為此,，科學(xué)家理論分析了它們依舊存活了數(shù)萬年的原因，提出了亞馬遜帆鰭鱸的一種“自救”理論――認(rèn)為它們偶爾會從其它品種的雄魚中獲取一些DNA,，以此來觸發(fā)繁殖,，以更新它們的基因庫。愛丁堡大學(xué)生物科學(xué)學(xué)院的勞倫斯·洛伊博士說：“我們的研究表明這些魚真有其特別之處,，還有特別的生存訣竅來幫助這種魚幸存下來,。也許是偶然與陌生客交配一下，以保持此物種的繁衍。未來的進(jìn)一步研究將給我們更多的答案,。”
洛伊博士補(bǔ)充說,，他們的發(fā)現(xiàn)還能幫助他們更多地了解其它物種是如何運(yùn)作的。“我想一件有趣的事情是我們更多地知道了其它物種也會使用同樣的訣竅來生存下來,。這可能有更普遍的重大意義,。”
此研究成果發(fā)表在最新一期的《BMC進(jìn)化生物學(xué)》雜志上。洛伊博士計(jì)劃采取更進(jìn)一步的數(shù)學(xué)檢測來繼續(xù)分析亞馬遜帆鰭鱸的自然習(xí)性,。
生物谷推薦原始出處：
BMC Evolutionary Biology 2008, 8:88doi:10.1186/1471-2148-8-88
Quantifying the threat of extinction from Muller's ratchet in the diploid Amazon molly (Poecilia formosa)
Laurence Loewe1,2 and Dunja K Lamatsch3,4,5,6
1Institute of Evolutionary Biology, School of Biological Sciences, University of Edinburgh, Ashworth Laboratories, King's Buildings, Edinburgh EH9 3JT, UK
2Centre for Systems Biology Edinburgh, School of Biological Sciences, University of Edinburgh, Darwin Building, King's Buildings, Edinburgh EH9 3JU, UK
3Universität Würzburg, Institute of Physiological Chemistry I, Biocenter, Würzburg, 97074 Würzburg, Germany
4Freshwater Biology, Royal Belgian Institute of Natural Sciences, Vautierstraat 29, B – 1000 Brussels, Belgium
5University of Sheffield, Department of Animal and Plant Sciences, Alfred Denny Building, Western Bank, Sheffield, S10 2TN, UK
6Austrian Academy of Sciences, Institute for Limnology, Mondseestrasse 9, 5310 Mondsee, Austria
Abstract
Background
The Amazon molly (Poecilia formosa) is a small unisexual fish that has been suspected of being threatened by extinction from the stochastic accumulation of slightly deleterious mutations that is caused by Muller's ratchet in non-recombining populations. However, no detailed quantification of the extent of this threat is available.
Results
Here we quantify genomic decay in this fish by using a simple model of Muller's ratchet with the most realistic parameter combinations available employing the evolution@home global computing system. We also describe simple extensions of the standard model of Muller's ratchet that allow us to deal with selfing diploids, triploids and mitotic recombination. We show that Muller's ratchet creates a threat of extinction for the Amazon molly for many biologically realistic parameter combinations. In most cases, extinction is expected to occur within a time frame that is less than previous estimates of the age of the species, leading to a genomic decay paradox.
Conclusion
How then does the Amazon molly survive? Several biological processes could individually or in combination solve this genomic decay paradox, including paternal leakage of undamaged DNA from sexual sister species, compensatory mutations and many others. More research is needed to quantify the contribution of these potential solutions towards the survival of the Amazon molly and other (ancient) asexual species.
