Like a Virgin, Prasad, Aarathi [free children's ebooks pdf .TXT] 📗

males to females in their host populations, usually by killing or feminizing the males. These include protozoa, which affect mosquitoes and amphipods, an order of tiny crustacean, most usually less than ten millimetres in size; spiroplasms, which affect fruit flies; enterobacteria in wasps; and rickettsiae in ladybird beetles. For most of the planet’s species, the sexes and reproduction are not always what they seem.

Then, there are those few animals that normally would have sex to reproduce, but don’t strictly have to do so. In recent years, the list of these animals has been steadily getting longer. It’s not that virgin birth as a phenomenon is necessarily increasing in the natural world; rather, that scientists have simply started to realize that some very large animals – not just insects – are able to reproduce without mates, should they need to.

On 14 December 2001, the list was extended in an exciting new way. Before then, virgin births had been documented in all of the jawed vertebrates – that is, animals with backbones and jaws. The exceptions, therefore, were the mammals and cartilaginous fishes, the latter of which include sharks and rays but also the aptly named chimaeras – peculiar-looking deep-sea rat-fishes and egg-laying ghost sharks that have glowing eyes and snouts like an elephant. But that December, an adult bonnethead shark gave birth to a normal, live female pup at the Henry Doorly Zoo in Nebraska.

The adult shark had been captured from the Florida Keys when she was not yet a year old. For the bonnethead shark (Sphyrna tiburo), that meant it was two years away from hitting puberty. Once captured, it had been raised in a tank at the zoo, in the company of only two other sharks – both female. Now, sharks of the hammerhead family, of which the bonnethead is a member, normally can store up sperm from a previous mating for as long as five months. But that would not have been possible for this female, as it was so young when it was caught. The other possibility that the zookeepers considered was that it may have both male and female genitals, as some humans do. But there again, it didn’t have any claspers, a kind of penis that a shark that is biologically both male and female could use to fertilize itself. There was only one other way a pup could have ended up in a tank full of adult female bonnethead sharks. And genetic tests later confirmed that the pup was in fact a virgin-born animal, the first of its type to be identified.

For obvious reasons, it is extremely difficult to spot a virgin birth in a wild animal population. Unless you are very lucky, and stumble on a female-only group that cannot possibly be accessed by males – the shark in a tank – reproduction by parthenogenesis in an animal that usually has sex is easy to miss. So it’s not surprising that the next reported virgin shark mother was once again found in captivity, seven years later, at the Virginia Aquarium, in Virginia Beach. This time the mother was an eight-year-old blacktip shark (Carcharhinus limbatus) named Tidbit; unfortunately, her parthenogenetic offspring was only discovered during Tidbit’s necropsy. Like the bonnethead shark mother, Tidbit had been caught in the wild when very young, less than a year old, and had reached sexual maturity in a tank at the aquarium. The shark had died during a routine physical examination – nothing had seemed amiss. When the body was cut open, it was found to be carrying a pup that was thirty centimetres (one foot) long and nearly full term. Like the bonnethead baby, DNA analysis revealed that the female blacktip foetus did not have a shred of genetic material from a father. There couldn’t have been, as there were no male blacktip sharks in the tank for the entire eight years that Tidbit had lived there.

Sharks are not the only new animals joining the parthenogenetic ranks. Two years before Tidbit’s examination, two virgin births in Komodo dragons at zoos in the United Kingdom were announced; since then, a third has occurred in Kansas. Komodo dragons (Varanus komodoensis) are the largest of all lizards; the adults can grow to a length of three metres (ten feet) and can weigh more than ninety kilograms (two hundred pounds). Yet, as wild Komodo populations have become smaller and more fragmented, these legendary creatures have come under threat of extinction. Today, there are fewer than four thousand Komodo dragons remaining in the wild, of which fewer than a thousand are believed to be mature females.

Because of these worrisome figures around the species’ future, at least fifty zoos had begun participating in an international breeding programme by the time the virgin births were discovered; it could be said that quite a few people were paying quite a bit of attention to Komodo sex life. In all of Europe, there were only two sexually mature female lizards: Flora at Chester Zoo and Sungai at London Zoo. Both had been bred in captivity, and were therefore crucial to the success of the European breeding programme. But what the zoo staff involved had not realized is that female Komodos can reproduce without a male.

It’s not that Komodos need males to lay eggs – much like chickens, it has long been known that some of the eggs Komodos lay will be unfertilized. But in 2006, the then zoo-keeper in Chester, Kevin Buley, took a clutch of twenty-five eggs that Flora had laid and incubated them ‘on a zoo-keeper’s whim’. It was a serendipitous moment for science, and, indeed, for Komodo conservation. Flora had never been with a male dragon. Yet of the twenty-five eggs that Buley fostered, eleven looked just like normally fertilized eggs would. And in January 2007, eight hatched into healthy male Komodo