Inbred kākāpō 'purge' bad genes, in better shape than expected - study

A small number of kākāpō related to those who survived isolated on Rakiura/Stewart Island for 10,000 years have turned out to be less-inbred than their relatives on the mainland.

The surprise finding has scientists wondering if inbreeding is all that bad - at least when it comes to the nocturnal, flightless parrot, native to New Zealand. 

Scientists from here and Sweden sequenced the genomes of 35 kākāpō descended from Rakiura birds and compared the results to the extinct mainland population. 

"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," said Stockholm University genetics researcher Nicolas Dussex. 

"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’ and that inbreeding may have facilitated it."

Inbred populations of any species that uses sexual reproduction tend to die out, as detrimental genes build up and aren't replaced. 

"The kākāpō are inbred and that is generally considered a bad thing - lower levels of genetic diversity correlate with things like lower population persistence," Dr Emma Carroll, Rutherford discovery fellow at the University of Auckland, told Newshub (she wasn't involved in the research). 

"But what's promising from this work is the Rakiura population seemed to be able to expel some of these harmful mutations from its genome, even when it had a really low population size. We call that purging. It's kind of positive, because it meant it could overcome some of those issues associated with low genetic diversity."

The research suggests that once a detrimental gene was "purged", it was unlikely to reappear - keeping the small population relatively healthy. 

"Our results are good news, not only for kākāpō but also for the conservation of other highly inbred and isolated species, because they suggest that it is possible, under some circumstances, for small populations to survive even if isolated for hundreds of generations," said Bruce Robertson of University of Otago, who has been digging into kākāpō genetics for 25 years.

An attempt to resurrect not just the population but the genetic diversity of the Rakiura population began with a single male found on the mainland, Richard Henry, who was introduced to the southern ladies in the late 1990s. 

While he was genetically distinct from the Rakiura birds, he also carried some "harmful mutations".

"Therefore, there could be a risk that these harmful mutations spread in future generations," said Love Dalén of the Swedish Museum of Natural History.

The hope is the diversity Henry brought will outweigh his bad genes. By sequencing the genomes of every bird on the island, the scientists can figure out which are least-closely related and "hopefully make lots and lots of kākāpō babies and grow the population... and creating safe spaces where there are a fewer predators and they can thrive", said Dr Carroll. 

"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," said Dr Dussex. "It thus gives us some hope for the long-term survival of the kākāpō as well as other species with a similar population history."

The research was published in Cell Genomics on Thursday.