Genome Sequence of the Little Bush Moa Illuminates Avian Evolution

Since discovering my first fossils in a stream behind the Baseball Hall of Fame in Cooperstown, New York, when I was 10, I’ve been fascinated with clues to past life. I was so excited to find what turned out to be worm borings that my mother trekked me up to a researcher at the American Museum of Natural History, who took the time to identify my specimens. And the next day, I wrote an essay in class about wanting to become an invertebrate paleontologist, flummoxing the poor teacher charged with encouraging a budding nerd.

I still have those fossils, nestled in compartments I built into a tattered yellow cigar box.

I didn’t grow up to become an invertebrate paleontologist, but a geneticist. And discovering the DNA sequence of a novel genome intrigues me in much the same way as those ancient worm borings did, but it’s even more telling, because genetic information reveals clues to the past and connects the ancient species to their modern descendants. Evolution.

That’s why a recent report in Science Advances captured my attention: “A nuclear genome assembly of an extinct flightless bird, the little bush moa.”

The researchers, from Harvard’s famed Museum of Comparative Zoology, extracted the ancient bird DNA from a toe bone at the facility. Their analysis provides novel glimpses into the backstory of avian evolution.

The little bush moa was about the size of a turkey, the smallest of its kind at about 60 pounds. Modern relatives are the ostrich, emu, and kiwi.

It is one of nine known species of moa, all extinct beginning about 700 years ago, with the arrival and spread of the Māori people in New Zealand, who called the birds moariki. The birds lived in lowland forests across the north and south islands, until Polynesian human settlers began arriving in the late 1200s, and their dogs vanquished the flightless birds.

“We can study modern birds by looking at them and their behavior. With extinct species, we have very little information except what their bones looked like and in some cases what they ate. DNA provides a really exciting window into the natural history of extinct species like the little bush moa. We’re pulling away the veil across the mystery of this species,” said senior author Scott Edwards, curator of ornithology at the museum.

The team used high-throughput DNA sequencing, the gold standard that has revealed the genomes of Neanderthals, the woolly mammoth, and the passenger pigeon. The technique shatters many genome copies into tiny pieces, overlapping the 10-base-long fragments to deduce the overall sequence, using some DNA from modern relatives for guides – especially modern moas and emus – as well as bacterial DNA to ease handling.

Reconstructing the bush moa genome required sequencing about 17 million genomes from 140 birds.

The genome sequencing showed the little bush moa’s closest still-living relative is the tinamou, from which it diverged genetically (most recently shared an ancestor) about 53 million years ago. That means that their closest relatives aren’t kiwis, as had been thought.

An example of the type of information that a long sequence of A, T, C, and G – the DNA bases – can reveal is insights into how the extinct birds sensed their environment.
Like many birds, the extinct moa had four types of cone photoreceptors in their retinas, bestowing not only color but also ultraviolet vision. Human eyes have three types of cones. We can’t see into the ultraviolet.

The birds also had a fine sense of taste, with receptors that brought them the ability to taste bitter and umami (sensory) foods.

Most surprising from the genome analysis was the complete absence of genes involved in constructing bones of the forelimb present in other birds, indicating that the animals were flightless. Perhaps the little bush moa’s genome can shed light on how inability to fly provided a survival advantage – or perhaps, in the long run, didn’t.

The little bush moa is already on its way to de-extinction efforts, using breeding strategies described in a 2018 article in the journal Genes, “De-Extinction,” by Ben Jacob Novak, of Revive and Restore. The bird joins the passenger pigeon, heath hen, giant tortoise, quagga (RL), and auroch (extinct cattle) in de-extinction efforts. (I wrote about the quagga effort here and resurrecting ancient floral scents here.)

Reports on the secrets revealed in ancient genome sequences always remind me of how important it is to encourage a child’s fascination with nature, especially discovery of clues to past life.