Flightless, ungainly, and famously bad at sex, the critically endangered kākāpō of New Zealand — the world’s heaviest parrots — are in surprisingly good genetic health after 10,000 years of inbreeding, according to new research.
An international team of geneticists, biologists, and ecologists recently looked at 49 of the birds’ genomes to understand how the small populations were faring genetically, given their near-extinction 30 years ago. The team came away surprised at how the species, which now totals just over 200, has avoided the kind of damaging mutations that plague other animals on the brink of extinction. Their research is published today in Cell Genomics.
“The main finding of this study is that, even though kākāpō are one of the most inbred and endangered bird species in the world, it has much fewer harmful mutations than expected,” said Nicolas Dussex, lead author of the paper and a researcher at the Centre for Palaeogenetics and Stockholm University, in an email to Gizmodo.
To explain this unexpected result, Dussex’s team suggests a counter-intuitive genetic phenomenon called purging, by which inbred populations end up having fewer harmful mutations in their genetic code rather than more.
“It seems that one factor favouring purging is the speed of the decline and the rate of increase of inbreeding,” Dussex added. “If inbreeding increases very rapidly, a large number of harmful mutations will be exposed to natural selection in a very short timespan … Conversely, if inbreeding increases gradually, harmful mutations are exposed little by little, over a larger number of generations and not in all individuals at the same time.” In other words, because kākāpō inbred over 10,000 years isolated on the islands of New Zealand, a fatal population crash due to genetic corruption never happened.
Kākāpō do not look like survivors. The bird, also called an owl parrot, fits into the same category as giant pandas and quokkas as creatures whose survival seems purely aesthetic, at least to the untrained eye.
Kākāpō like to eat fruit, especially the rimu fruit, nest in ground-level shelters, and can live quite long, perhaps up to 80 years. Kākāpō are often infertile and sometimes have poor judgment — one kākāpō named Sirocco famously tried to mate with a wildlife photographer’s head.
Hunted by invasive mustelids (which were introduced by humans to cull booming rabbit populations), kākāpō easily could have followed in the footsteps of the similarly ground-bound dodo, but surviving populations of the birds were moved to predator-free islands around New Zealand in the 1980s. Since then, attempts to reduce inbreeding and maintain genetic diversity in the minuscule population have been paramount.
“We show that the single male survivor from the mainland, Richard Henry, has more harmful mutations than Stewart Island birds,” said paper co-author Love Dalén, a researcher at the Centre for Palaeogenetics and the Swedish Museum of Natural History, in a statement. “Therefore, there could be a risk that these harmful mutations spread in future generations.”
Richard Henry the kākāpō was found in Fiordland in southwestern New Zealand, and his genetic diversity and virility were imperative in pulling the birds back from extinction. At the same time, though, Henry’s DNA harbours more harmful mutations than kākāpō from Stewart Island. (Richard Henry is named after a human who devoted much of his life at the turn of the 20th century to saving the species. Henry the human’s work has been resumed by a handful of New Zealand conservationists, many of whom co-authored the paper published today.)
The kākāpō’s genetic success story could be contrasted with that of the Isle Royale wolves, whose population of about 50 in 2011 plummeted to just two in 2016 after a new individual messed with the genetics of the already dangerously inbred group. A study of that situation, published last year in Evolution Letters, indicated that sometimes pushing high genetic diversity too quickly in a group with low genetic diversity can cause the population to collapse.
It’s also, perhaps, a warning for the kākāpō, as the bird is hardly out of the proverbial woods and, genetic diversity aside, has to worry about the predatory stoats and weasels that prowl its territory. The recent research will help to refine the breeding program approach, Dussex said, and new island populations could be established now that researchers have a better understanding of how all those in the current population relate.
If researchers manage to keep the kākāpō population genetically healthy, it’d be a big win in the battle for the animal’s survival. There are many threats ahead, but the portly green bird has a chance.