为适应环境，“面包海星”在漂流的过程中进化出了自我交配的能力。7月18日，一项在线发表在英国《皇家学会报B》（Proceedings of the Royal Society B:Biological Sciences）杂志上的研究称，这些海星进化成卵胎生雌性同体的速度，在海洋动物的物种形成中，可以算得上是已知最快的之一。
数千年前，当一小群幼体海星在澳大利亚海岸附近因被海水冲走而脱离其“父母”后，事实证明它们比汤姆·汉克斯在电影《荒岛余生》中所表现的更为足智多谋。
这些腕足粗短、以体形圆胖而著称的“面包海星”，在漂流的过程中没有抱团聚集成排球状，相反却发展出了自我交配的能力。
为了查明这些海星是何时、何地从它们的家族中脱离的，该研究团队分析了近400只海星的组织中的DNA，其中一半海星属于祖先种属Cryptasterina pentagona，一半属于新的种群C. hystera。
通过分析这两个物种DNA序列之间的进化关系，研究人员能够推断，在最多2.2万年前，C. hystera已在大堡礁附近从C. pentagona的南方支系中脱离出来。
大约6000年前，C. hystera成为了一个独特的物种。从进化标准来说，这可以称得上是闪电般的适应速度。
大多数海星为雌雄异体，精子和卵子在水中相遇完成受精，形成新的生命。从受精的卵子中孵化出的幼体，会随海水四处漂流，以浮游生物为食，最后成长为海星。
海星还有一种特殊的能力——再生。海星的腕、体盘受损或自切后，能够重新生成一个新的海星。因此，某些种类的海星通过这种超强的再生方式演变出了无性繁殖的能力。（生物谷Bioon.com）
doi:10.1098/rspb.2012.1343
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Extraordinarily rapid life-history divergence between Cryptasterina sea star species
Jonathan B. Puritz1,*, Carson C. Keever2, Jason A. Addison3,4, Maria Byrne5, Michael W. Hart2, Richard K. Grosberg3 and Robert J. Toonen1
Life history plays a critical role in governing microevolutionary processes such as gene flow and adaptation, as well as macroevolutionary processes such speciation. Here, we use multilocus phylogeographic analyses to examine a speciation event involving spectacular life-history differences between sister species of sea stars. Cryptasterina hystera has evolved a suite of derived life-history traits (including internal self-fertilization and brood protection) that differ from its sister species Cryptasterina pentagona, a gonochoric broadcast spawner. We show that these species have only been reproductively isolated for approximately 6000 years (95% highest posterior density of 905–22 628), and that this life-history change may be responsible for dramatic genetic consequences, including low nucleotide diversity, zero heterozygosity and no gene flow. The rapid divergence of these species rules out some mechanisms of isolation such as adaptation to microhabitats in sympatry, or slow divergence by genetic drift during prolonged isolation. We hypothesize that the large phenotypic differences between species relative to the short divergence time suggests that the life-history differences observed may be direct responses to disruptive selection between populations. We speculate that local environmental or demographic differences at the southern range margin are possible mechanisms of selection driving one of the fastest known marine speciation events.
