An international team of researchers has successfully sequenced and analyzed the genome of the kākāpō (Strigops habroptilus), a flightless parrot endemic to New Zealand. Published in the journal Cell Genomics, their results shows that even after 10,000 years of inbreeding, the species is in surprisingly good genetic health.
The kākāpō (Strigops habroptilus). Image credit: Jake Osborne.
New Zealand was one of the last landmasses colonized by humans.
Following Polynesian colonization circa 1360 CE and European colonization in the 1800s, and the resulting overhunting and introduction of mammalian predators, New Zealand experienced major extinction events of endemic species.
The kākāpō was widespread before human arrival and likely numbered in the hundreds of thousands.
By 1995, the species was reduced to 51 birds: 50 kākāpō from the isolated Stewart Island and one single male, named Richard Henry, from the extinct mainland population.
Richard Henry and 39 Stewart Island birds were the only kākāpō to reproduce and are thus the ancestors of all birds born since 1995.
As of 2021, only 201 individuals survive and are managed on island sanctuaries.
“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 Dr. Nicolas Dussex, a researcher at the Center for Palaeogenetics and Stockholm University.
“Our data show 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.”
“In small populations, this type of harmful mutation can lead to genetic diseases,” said Professor Love Dalén, a researcher at the Center 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.”
In the study, the scientists sequenced and analyzed 35 modern kākāpō genomes from the sole surviving island population and 14 genomes from the extinct mainland population.
In small populations, scientific theory suggests that deleterious mutations may accumulate, leading to an increased risk for extinction. But it’s also possible that detrimental gene variants, exposed through inbreeding, could instead be eliminated from the population by natural selection, a process known as purging.
The authors found that the latter possibility more accurately describes what’s happened in the case of the kākāpō.
“We show that the single male survivor from the mainland, Richard Henry, has more harmful mutations than Stewart Island birds,” Professor Dalén said.
“Therefore, there could be a risk that these harmful mutations spread in future generations.”
“On the other hand, Richard Henry is also genetically distinct and may carry useful genetic diversity. This means that careful consideration must be given to pros and cons.”
“It will therefore be important to carefully monitor the health and genomes of Richard Henry’s offspring to ensure they don’t introduce harmful mutations to the island population.”
Nicolas Dussex et al. Population genomics of the critically endangered kākāpō. Cell Genomics, published online September 8, 2021; doi: 10.1016/j.xgen.2021.100002