BMC：神奇鱼类7万年从未交媾
据英国《每日邮报》报道，一项新研究表明一种神奇鱼类全是女儿身，7万年来从未交媾，但一直繁衍至今，在公然挑战达尔文的进化论。这种鱼就是亚马逊帆鳍鲈（Molly）。
英国科学家表示，一般来说，有性物种若以无性繁殖，过不了几代就会出现基因残障，最后绝种。按理说亚马逊帆鳍鲈应该绝种，但它们巧妙地利用遗传基因来得以幸存。
众所周知，有雄鱼精子才能形成胚胎，但亚马逊帆鳍鲈的所有后代似乎没有爸爸的一点DNA，而是全部继承了妈妈的基因物质。
但亚马逊帆鳍鲈仍旧繁衍在美国德州东南部和墨西哥西北部的河流中，这令科学家大为意外。
为解开这一谜团，英国爱丁堡大学的科学家通过高性能的计算机系统来研究复杂的数学模型，以分析亚马逊帆鳍鲈的这一特别案例。根据模型计算亚马逊帆鳍鲈数千代鱼的基因变化情况，科学家得出它们应该在7万年前就灭绝了。
为此，科学家理论分析了它们依旧存活了数万年的原因，提出了亚马逊帆鳍鲈的一种“自救”理论――认为它们偶尔会从其它品种的雄鱼中获取一些DNA，以此来触发繁殖，以更新它们的基因库。爱丁堡大学生物科学学院的劳伦斯·洛伊博士说：“我们的研究表明这些鱼真有其特别之处，还有特别的生存诀窍来帮助这种鱼幸存下来。也许是偶然与陌生客交配一下，以保持此物种的繁衍。未来的进一步研究将给我们更多的答案。”
洛伊博士补充说，他们的发现还能帮助他们更多地了解其它物种是如何运作的。“我想一件有趣的事情是我们更多地知道了其它物种也会使用同样的诀窍来生存下来。这可能有更普遍的重大意义。”
此研究成果发表在最新一期的《BMC进化生物学》杂志上。洛伊博士计划采取更进一步的数学检测来继续分析亚马逊帆鳍鲈的自然习性。
生物谷推荐原始出处：
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.
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