After 10,000 years of inbreeding, the kākāpō is hanging on

The kākāpō (Strigops habroptila), the world’s heaviest and arguably dumbest parrot, doesn’t seem to suffer from a history of inbreeding, according to a study published in Cell Genomics.

The critically endangered bird is native to Aotearoa/New Zealand, and is known for clumsily falling out of trees (it is flightless), freezing in the face of impending predator attack, and having an incredibly complicated breeding cycle. Sadly, due to predators and ecological changes, the birds’ population dwindled to just 51 by 1995. Among these, 50 lived on the island of Rakiura (Stewart Island) in the south of the country. The other was a single mainland male, called Richard Henry.

Richard Henry was moved down to Rakirua to meet the ladies, and, thanks to his prowess, the numbers have now grown to 200 individuals. Unfortunately, this means the group is also one of the most inbred populations in the world.

But in good news, an international team of researchers has analysed the genomes of 49 kākāpō – 35 from Rakiura and 14 from the extinct mainland population – and found that they haven’t actually accumulated bad mutations from inbreeding at all. In fact, they even got a little better.

“Even though the kākāpō is one of the most inbred and endangered bird species in the world, it has many fewer harmful mutations than expected,” says Nicolas Dussex, a researcher at the Centre for Palaeogenetics and Stockholm University.

“Our data shows that the surviving population on Stewart Island has been isolated for approximately 10,000 years and that during this time, harmful mutations have been removed by natural selection in a process called ‘purging’. Inbreeding may have facilitated it.”

“In small populations, this type of harmful mutation can lead to genetic diseases,” adds Love Dalén, also of the Centre for Palaeogenetics and Swedish Museum of Natural History.

“Our finding of a reduced number of harmful mutations is therefore important, since it means that inbreeding in the present-day population is likely to have less severe impact than we had initially thought.”

A kākāpō being cute. Credit: Jake Osborne

With so few kākāpō left, this is incredibly useful information, because it means that the best candidate breeding pairs can be selected based on genetics without having to worry too much about how closely related the pair are.

“While the species is still critically endangered, this result is encouraging as it shows that a large number of genetic defects have been lost over time and that high inbreeding alone may not necessarily mean that the species is doomed to extinction,” says Dussex.

“It gives us some hope for the long-term survival of the kākāpō as well as other species with a similar population history.”

And, of course, Richard Henry still features in the story.

“We show that the single male survivor from the mainland, Richard Henry, has more harmful mutations than Stewart Island birds,” Dalén says. “Therefore, there could be a risk that these harmful mutations spread in future generations.”

This is particularly important because Richard Henry sired the first babies and kicked off the whole breeding program. If his offspring also have some bad mutations, it means they can be effectively paired with others to counteract problematic effects. On the other hand, because Richard Henry came from the mainland, not Rakiura, he also had some important genes that promote genetic diversity. Either way, his genes are still going strong.

The researchers plan to keep studying other endangered and inbred animals to determine if the kākāpō is a rare exception.