Casque-headed iguana at Telford zoo produces eight hatchlings without mating, zoo says

A female casque-headed iguana at the Exotic Zoo in Telford, Shropshire, has produced eight hatchlings despite never having been housed with a male, zoo staff said, a phenomenon the centre described as one of the rarest events in the animal kingdom.

Scott Adams, managing director of the Exotic Zoo, said the eggs were laid by the long-term resident, known as Carol, and placed in an incubator. "A couple of months later we got eight little babies running around," he told BBC Radio Shropshire, calling the event "a virgin birth, shall we say." He added, "We’ve got eight little babies but we’ve only got a female casque-headed iguana."

The zoo said the August birth is thought to be the result of parthenogenesis, a form of asexual reproduction in which offspring develop from unfertilised eggs. Genetic testing by the zoo indicated the hatchlings are "identical" clones of their mother and are all female, which is consistent with parthenogenetic reproduction in reptiles. "This is what happens with parthenogenesis — there's no boys in there, they're all girls," Adams said.

Ryan Jordan, head keeper at the Exotic Zoo, said the striking hatchlings display lime-green and jet-black striping. The newborns are being kept in controlled temperature and humidity conditions to simulate their tropical Central American habitat, while Carol remains on public display. The zoo said it expects to transfer the juveniles to other institutions after a period of rearing, in response to interest from other collections.

Casque-headed iguanas are primarily arboreal lizards native to the rainforests of Mexico and Central America. Zoo staff noted the species' long legs and tail — which can make up about 60% of body length — are adaptations for life in the canopy. Like many reptiles, casque-headed iguanas lay eggs and provide no parental care after laying, a life-history trait the zoo described as contributing to rapid dispersal of offspring in the wild.

Parthenogenesis is rare but has been documented in a range of animal groups. Scientists have recorded facultative parthenogenesis in insects and birds such as mayflies and turkeys, and in reptiles including pythons and boa constrictors. Recent captive cases cited by the Exotic Zoo and news reports include a swell shark born in an all-female tank in Louisiana and a boa constrictor in Portsmouth that gave birth despite no recorded opportunity to mate. A stingray in North Carolina was once reported to be pregnant via parthenogenesis, though later scrutiny raised doubts about that case and the animal subsequently died of a reproductive disease.

Researchers do not fully understand the triggers or genetic mechanisms that allow parthenogenesis to occur in some species and not others. Some studies suggest the process may be more likely when individuals are isolated or when populations are small and mates are scarce, potentially providing a short-term route to reproduce. "We actually still don't know exactly what it is that makes virgin birth possible in some animals but not in others," Professor Russell Bonuriansky, an ecologist at the University of South Wales in Australia, told the Daily Mail. "But we do have some idea of what is required."

Zoo staff emphasised that while parthenogenesis can produce viable offspring, it yields reduced genetic diversity because the young are genetically very similar to the mother. That similarity can affect long-term population resilience to disease or environmental change, a factor conservationists weigh when assessing the implications of parthenogenetic reproduction for threatened species.

The Exotic Zoo said it will continue to monitor the hatchlings closely as they grow and prepare to place them in other accredited collections. The centre described the event as an opportunity to study a rare reproductive outcome and to raise public awareness about the natural history of lesser-known reptile species.