CAN'T find a mate? Try parthenogenesis. The type of asexual reproduction may be part of an extreme survival strategy for sharks.
找不到配偶？那就试试单性生殖！无性生殖也许将成为鲨鱼的最终生存方式。
In parthenogenesis, females' eggs start dividing without being fertilised. This produces daughters that are genetically similar to themother. It was first oberved in a captive hammerhead shark in 2001, but this was an isolated incident, and the shark pup died after three days,making it difficult to say much about its evolutionary significance.
在单性生殖中，雌性动物的卵无需受精即开始分裂。这会产下基因与母亲相同的女儿。单性生殖最初是在2001年捕获的一头锤头鲨身上发现的，不过，这只是一个孤立的事件，而且，鲨鱼幼崽3天后就死了，因此，要对单性生殖的进化意义作比较多的阐述有点勉为其难。
Kevin Feldheim at the Field Museum in Chicago, and an international team of colleagues, has now shown that the inc ident was not exceptional and sharks born from a virgin mother can survive for many years (Journal of Heredity, vol 101, p 374).
供职于芝加哥菲尔德博物馆和遗传研究国际组织的Kevin Feldheim表示，此次事例并非异常，由单性生殖母鲨产下的幼鲨可存活多年（见《遗传杂志》第101期，374页）。
The team was inspired by the 2001 birth to keep eggs produced by a captive white-spotted bamboo shark at the Belle Isle Aquarium of the Detroit Zoological Institute. The female had never encountered a male during her adult life and biologists had assumed the eggs were infertile. To their surprise seven incubated eggs produced two pups that survived five years before they were transferred to another facility. Genetic analysis confirmed that they were parthenogenesis.
受2001年锤头鲨幼崽的启发，该组织将一头在底特律动物学研究所贝尔岛水族馆捕获的白斑竹子鲨所产的卵作了保留处理。这头母鲨在其成年期中未曾遇到过一头雄鲨，生物学家们曾想当然地认为这些卵没有生育力。但令他们惊奇的是，7只孵化的卵中竟孵化出了两头幼鲨，而这两头幼鲨在被转移到另一个水族箱之前存活了5年。遗传分析确认，它们系单性生殖。
"This suggests that parthenogenesis is a viableshark survival strategy," says Paulo Prodöhl of Queen'sUniversity Belfast, UK, who is investigating a possible case of virgin birth in the whitetip reef shark.
“这暗示着单性生殖将成为行之有效的鲨鱼繁殖法，”英国贝尔法斯特女王大学正研究白顶礁鲨单性生殖可能性的Paulo Prodöhl说。
Modern sharks have been on Earth for several hundred million years. One theory is that switching from sexual reproduction to virgin birth might have helped these ancient creatures survive so long. Prodöhl suggests virgin birth could have been a safeguard mechanism. Several shark species live in single-sex groups and he says parthenogenesis may have ensured that isolated populations of females could survive without males.
现代的鲨鱼在地球上已存活了几亿年。一种理论言称，或许是有性生殖到单性生殖的转变才帮助了这些远古的生物存活了这么长的时间。Prodöhl认为，单性生殖可能已成为一种保障机制。有几个鲨鱼物种以单性群的方式生存，他还说，单性生殖或许可保证隔离的雌鲨种群不靠雄鲨也能繁殖。
注：本文原文选自http://www.newscientist.com，译文为本人原创。
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