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（法新社華盛頓十四日電） 研究人員今天證實，一條小鯊魚似乎是在母鯊沒有與公鯊交配的情況下懷孕出生。這也是研究人員發現的第二個類似案例。據「魚類生物期刊」週末的一篇報導，這項研究似乎顯示，母鯊可以在沒有公鯊讓卵受精的情況下生殖。這項研究報告的主要作者，紐約州立大學海洋保育科學研究所鯊魚專家柴普曼說，對這條幼鯊進行的DNA測試證實它沒有父親。這條小鯊魚是一條名叫「提蒂」的黑尖端母鯊魚的後代，這條母鯊已在維吉尼亞州一家水族館生活了八年，但從來沒有與公鯊魚接觸過。科學家說，這是經證實鯊魚以單性生殖懷孕的第二個案例，所謂單性生殖是一枚未受精的卵發展成一個新個體的過程。直到現在，一般相信，單性生殖只會發生在某些特定的昆虫、蜘蛛、蜈蚣和甲殼類動物身上。

There are different types of shark egg development:

• Viviparity(胎生)- The eggs hatch inside the female's body and the babies are fed by a placenta which transfers nourishment from the mother to the babies (via an umbilical cord which is connected to the baby shark behind the between the pectoral fins). The placenta helps transfer nutrients and oxygen from the mother's bloodstream and transfers waste products from the baby to the mother for elimination. Viviparous sharks give birth to live young. The number of pups in a litter ranges from 2-20 or more. Examples of viviparous sharks include the Bull sharks, Whitetip reef shark, Lemon shark, Blue shark, Mako, Porbeagle, Salmon shark, the Silvertip shark, and Hammerheads. Although long thought to be oviparous (an egg 14 inches (36 cm) long was once found), Whale sharks are viviparous and pregnant females have been found containing hundreds of pups.
• Oviparity(卵生)- These sharks deposit eggs in the ocean which will hatch later if they are not eaten by predators. The eggs are not guarded by either parent. Shark eggs (sometimes called "mermaid's purses") are covered by a tough, leathery membrane. Their shape ranges from pouch-like to screw-shaped (like the California hornshark and the Port Jackson shark). Some eggs (like those of catsharks) have tendrils that attach the egg to objects on the sea bed. The egg has a yolk that feeds the embryo, very much like a chicken egg. Oviparous sharks include the Zebra shark, the catsharks, swellshark, the necklace carpetshark, some Epaulette sharks, and the Hornshark.
• Aplacental Viviparity (Ovoviviparous)(卵胎生)- In these animals, the eggs hatch and the babies develop inside the female's body but there is no placenta to nourish the pups. The pups eat any unfertilized eggs and each other (they are oviphagous). Very few pups in a litter survive until birth due to this form of sibling cannibalism. Great white sharks, sawsharks, Mako, crocodile sharks, Cookiecutter sharks, Pelagic thresher, Greenland shark, Gummy shark, Soupfin shark, Pacific Angelshark, Pygmy sharks, Nurse shark, Tiger shark, and Sand tiger sharks reproduce this way.