為適應(yīng)環(huán)境,，“面包海星”在漂流的過程中進化出了自我交配的能力。7月18日,，一項在線發(fā)表在英國《皇家學(xué)會報B》（Proceedings of the Royal Society B:Biological Sciences）雜志上的研究稱,，這些海星進化成卵胎生雌性同體的速度，在海洋動物的物種形成中,，可以算得上是已知最快的之一,。
數(shù)千年前，當一小群幼體海星在澳大利亞海岸附近因被海水沖走而脫離其“父母”后,，事實證明它們比湯姆·漢克斯在電影《荒島余生》中所表現(xiàn)的更為足智多謀,。
這些腕足粗短、以體形圓胖而著稱的“面包海星”,，在漂流的過程中沒有抱團聚集成排球狀,，相反卻發(fā)展出了自我交配的能力。
為了查明這些海星是何時,、何地從它們的家族中脫離的,，該研究團隊分析了近400只海星的組織中的DNA，其中一半海星屬于祖先種屬Cryptasterina pentagona,，一半屬于新的種群C. hystera,。
通過分析這兩個物種DNA序列之間的進化關(guān)系，研究人員能夠推斷,，在最多2.2萬年前,，C. hystera已在大堡礁附近從C. pentagona的南方支系中脫離出來。
大約6000年前,，C. hystera成為了一個獨特的物種,。從進化標準來說，這可以稱得上是閃電般的適應(yīng)速度,。
大多數(shù)海星為雌雄異體,，精子和卵子在水中相遇完成受精，形成新的生命,。從受精的卵子中孵化出的幼體,，會隨海水四處漂流，以浮游生物為食,，最后成長為海星,。
海星還有一種特殊的能力——再生。海星的腕,、體盤受損或自切后,，能夠重新生成一個新的海星。因此,，某些種類的海星通過這種超強的再生方式演變出了無性繁殖的能力,。（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.
