Volcanic mountains

Volcanic supereruptions changed the genetics of the Kiwi bird

When two massive volcanic eruptions blanketed New Zealand in ash, they forever changed the genetics of the North Island’s brown kiwi bird, according to a new study from the University of Toronto Scarborough.

The population of the North Island brown kiwi (Mantelli Apteryxlisten)) is divided into four distinct lineages that inhabit different parts of the North Island of New Zealand. We did not know why these four groupings exist. While humans have destroyed much of the brown kiwis’ habitat and continue to contribute to their endangered status, their impact cannot fully explain the birds’ genetic distinctions. The island’s indigenous Maori have inhabited the island for around 700 years, while Europeans only began immigrating in large numbers around 160 years ago, far too recently to explain the discrepancy. Now researchers have found that two volcanic eruptions have wiped out most of the birds and isolated the survivors, leaving few to pass on their genes.

“You can easily tell which region of the island or which population the bird comes from by looking at its DNA. They are quite strongly differentiated considering they are the same species,” explains the author of the ‘study. Dr. Jordan Bemmels. “What we found allows us to say that these volcanoes had an impact on the brown kiwi, which persists to the present day.”

The Taupo Volcano, in the center of New Zealand’s North Island, produced two of the most violent eruptions in the world in geologically recent times. About 30,000 years ago, the first massive eruption covered the North Island with a thick layer of ash and igneous rock. Around 2,000 years ago, the volcano erupted again, with New Zealand’s largest eruption in 20,000 years. The Taupo volcano is considered still active.

Researchers examined the genetics and locations of 57 brown kiwi specimens collected by New Zealand conservation officials during the 1980s to 2000s. Bemmels used a supercomputer to build 2D maps of the island, then placed the kiwi, along with its genetic data, in their current location.

Bemmels included the habitat characteristics the birds need to survive, their tendency to stay close to their birthplace, and other migration patterns in the model. He then added the vast impact of the two volcanic eruptions – from the number of brown kiwi trees the blast could have killed to how it would have made areas of the island uninhabitable.

The computer simulated the eruptions and compared 12 possible models of how the birds might have been impacted. Bemmels then determined which result placed the specific brown kiwi lines closest to where they are today with similar genetic characteristics.

“It’s very different from other genetic simulation methods, where populations are modeled hypothetically and there is no spatial component,” says Bemmels. “As far as I know, no one has built the model of a natural disaster like this and then seen how it affects genetic diversity and the distribution of genetic groups.”

The most likely explanation was that the first eruption wiped out most of the birds, leaving a few on the fringes of the island. The surviving groups most likely remained isolated from each other because they were separated by natural barriers such as rivers and mountains, but eventually came back into contact for thousands of years. On a smaller scale, the second eruption had a similar impact: death, further isolation and stronger genetic signatures as survivors passed on their genes.

The results also suggest that the kiwi slowly began to retreat towards the center of the island, recolonizing the land as it recovered from the eruptions. Over several generations, they passed on the specific genetic signatures found today.

The study challenges the idea that only long-term geological changes such as climate change, glaciers or the formation of mountain ranges can impact a species over centuries.

“People tend to focus on very slow changes,” Bemmels says. “It could open the door for people to explore how major disasters that wipe out populations very quickly could leave a legacy for other species – and try to see if what we found is really the exception.”

The paper “Legacy of supervolcanic eruptions on the genetic structure of the brown kiwifruit population” is published in Current biology (2022). Material provided by the University of Toronto.