Volcanic mountains

U of T researcher examines how two volcanic eruptions forever changed the flightless brown kiwi

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

Brown kiwis are divided into four distinct lineages that inhabit different parts of New Zealand’s North Island. It is not known why these four groups exist, but it is well known that the birds survived two massive volcanic eruptions.

The researchers found that the eruptions wiped out most of the birds and isolated the survivors, leaving few to pass on their genes.

“You can easily tell which area of ​​the island or which population the bird is from by looking at its DNA. They are quite strongly differentiated considering they are the same species,” explains Jordan Bemmellead author of the study and post-doctoral researcher in the professor’s laboratory Jason Weir at the U of T Scarborough.

“What we found allows us to say that these volcanoes had an impact on the brown kiwi, which persists to the present day.”

A supercomputer helps illustrate the devastation of the volcano

About 30,000 years ago, the Taupo supervolcano blanketed swaths of the island in thick layers of ash and igneous rock in a massive eruption that spewed out more than 1,000 cubic kilometers of ash and of particles. The volcano blanketed the landscape with an eruption ten times smaller nearly 2,000 years ago.

The study, Posted in Current biologyexamined the genetics and locations of 57 brown kiwis 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 , as well as its genetic data, to their current location.

Bemmels provided information on the brown kiwi, a stocky, flightless bird. This included the habitat characteristics they need to survive, their tendency to stay close to their birthplace, and other migration patterns. 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 impacts genetic diversity and the distribution of genetic groups.”

Brave birds come together over the centuries

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.

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 native Maori have inhabited the island for around 700 years, while Europeans only started immigrating in large numbers around 160 years ago – far too recently to explain the discrepancy.

In fact, Bemmels seems to have confirmed a theory previously developed by the Weir Lab: the species was already beginning to deviate into four lineages, but the eruptions quickly intensified the division.

Funded in part by an NSERC Acceleration Grant and Discovery Grant, 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,” says Bemmels. “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.”