Life has found a way – in Telford’s Exotic Zoo. A casque-headed iguana has given birth to eight babies at the Shropshire wildlife park, but without any contact with a male, via a phenomenon called parthenogenesis.
“When we confirmed the eggs were fertile without any contact with a male, our jaws hit the floor,” zoo owner Scott Adams told the BBC. “For us, it’s a powerful reminder that life finds a way in the most unexpected circumstances.”
What is parthenogenesis? A type of asexual reproduction, in which females create offspring without fertilisation from male sex cells. The unfertilised eggs develop into embryos that are genetic clones of the mother: so basically, the female clones herself.
Parthenogenesis actually predates sexual reproduction, which evolved to introduce more genetic variation. It’s more common in plants or invertebrates than vertebrates, but has been observed among fish, snakes, sharks, lizards and even birds. What is “mind-boggling is that parthenogenesis isn’t even that rare”, said the Smithsonian Institution’s National Museum of Natural History. It was first documented in Komodo dragons in 2006, but has since been seen in all “vertebrate lineages” except mammals.
In January, a baby swell shark, Yoko, was born at Shreveport Aquarium even though the two females in the tank “had not been in contact with a male in over three years”, a spokesperson for the Louisiana attraction said. Yoko’s birth could have been the result of delayed fertilisation: females of many shark species can store sperm inside themselves for months or even years. But there have been documented cases of parthenogenesis involving more than half a dozen shark species.
So what kicks it off? “In general, we think parthenogenesis is a last-ditch effort for a female to pass on its genes, so when a female is isolated from conspecific males, she is able to undergo parthenogenesis,” Kevin Feldheim of Chicago’s Field Museum told NPR. “How parthenogenesis kicks in or what cues the females use to begin the process remains to be discovered.”
Organisms born via parthenogenesis, known as parthenotes, “don’t have the best track record when it comes to survivorship or fitness”, said the Smithsonian. Every zebra shark parthenote has died before reaching sexual maturity. However, one female white-spotted bamboo shark not only survived to sexual maturity but also gave birth through parthenogenesis.
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