How Lugging a Liquid Nitrogen Tank into the Amazon Helped Spark Ornithology’s Genetic Revolution

Almost 40 years ago, Smithsonian zoologist Gary Graves collected tissue samples in the jungle that formed the nucleus of the museum’s DNA collection

A wire-tailed manakin perches on a branch in the Amazon Rainforest. Murray Cooper, Smithsonian's National Zoo

In 1986, ornithologist Gary Graves and a team of Smithsonian biologists descended into a remote stretch of Brazil’s Amazon basin in search of birds. Over the next seven weeks, Graves caught a case of malaria, bathed in tributaries teeming with piranhas, and endured many of the other hardships that had plagued explorers in the region for centuries.

But the birds made it all worth it. The Amazon rainforest is home to more than 1,500 avian species, including multicolored macaws, broad-billed toucans, radiant trogons and hefty harpy eagles. Graves collected heart, liver and muscle samples from the different birds he encountered during the expedition. To keep the tissue samples cool in the muggy wilderness, he stored them in a tank of liquid nitrogen he had lugged into the Amazon.

Gary Graves on the search for birds during an expedition in the rainforests of Jamaica. Gary Graves, NMNH

Graves, now the curator of birds at the National Museum of Natural History, had harvested a gold mine of genetic data from the jungle. He had planned to analyze tissue extracts using protein electrophoresis, a then state-of-the-art technique to separate proteins by their size using an electrical charge. In 1986, in-depth laboratory techniques to sequence DNA were not invented yet.

The lack of affordable and accurate genome-sequencing techniques obscured the true value of these samples for decades. But as DNA sequencing processes improved, Graves and his colleagues were finally capable of realizing the scientific potential of the samples collected on that fateful expedition: “You'd never have guessed that these little tubes of frozen tissue that I brought back almost an entire lifetime ago would eventually be useful for anything like that,” Graves said.

A pair of green aracari birds, which sport a serrated bill, in the National Zoo’s Amazonia exhibition. Smithsonian's National Zoo
The Amazonian tissue samples became the nucleus of the Smithsonian’s Biorepository, a collection of more than 4.2 million vials of frozen cells housed in large vats of liquid nitrogen at the museum’s offsite facility. The samples Graves collected also helped launch the Bird 10,000 Genome (B10K) Project, an international effort by researchers in the United States, Denmark and China to sequence the genomes, or complete genetic blueprints, of all of the roughly 10,500 known species of birds, including everything from parrots and penguins to cassowaries and cuckoos.

Today, there may be no bigger DNA storehouse on Earth than the National Museum of Natural History

In the years since the B10K project launched in 2015, Graves and his colleagues have published a plethora of papers that outline the genomes of some 363 species of birds and counting. Each of these genetic datasets are publicly available to researchers around the world to use in their own studies. As they build up this sprawling genetic archive, the B10K researchers have been able to ask large-scale questions about how birds have responded to past environmental change, which may provide clues on how feathered fauna will fare in the future.

A hawk-headed parrot, a small Amazonian parrot, chows down on a flower at the National Zoo. Smithsonian’s National Zoo

In the past few months, Graves and his colleagues published a pair of papers in the Proceedings of the National Academy of Sciences and Nature Ecology and Evolution that use genetics to infer how 263 different species of birds responded to climate change over the past million years. The team measured specific traits like body size, egg number and bill length for the different bird species. They then used the genetic data to model how the populations of each bird had fluctuated over the past million years.

According to Graves, this allowed them to make observations about which traits were beneficial during specific climate conditions. “It’s a way of gaining insight on what we might expect if the earth heats up or cools to levels observed in the distant past and how that might affect these communities of birds,” Graves said. “If we know what happened in the past, then we might be able to forecast what to expect in the future.” For example, they found that big-bodied birds had to sweat out an intense warming spell roughly 130,000 years ago that largely benefited smaller birds.

The museum’s bird collection is the third largest in the world and has representatives of about 85% of the world's bird species. Jack Tamisiea, NMNH

To Graves, the questions that could be answered utilizing these genetic datasets are endless. With the genomes of more than 2,000 additional species currently in the sequencing pipeline, his collaborative team plans to incorporate even more species into these models to provide a framework for the future of everything from bustards to zebra finches around the world.

The project also illustrates the long scientific shelf life of museum specimens. In 1992, Graves published an influential letter in Science that made the case that natural history museum collections are “valuable storehouses of DNA” that had largely been overlooked  by molecular researchers.

“What I like about this research is that it is the end result of scientific processes that started more than 35 years ago.” – Gary Graves, Research Zoologist and Curator of Birds

There may be no bigger DNA storehouse on Earth than the National Museum of Natural History, whose more than 146 million specimens — which includes pickled crocodiles, thylacine pelts and more than 640,000 bird specimens — are brimming with crucial data points just waiting to be examined. “This is a very cool way that the Smithsonian’s collections are contributing to the next generation of cutting edge science,” he said.

A drawer of scarlet macaw specimens from the Amazon in the museum’s bird collection. Jack Tamisiea, NMNH

“Without the kinds of genetic resources preserved in this museum, much of this work wouldn't be possible,” Graves said. “There's no workarounds for this stuff, you either have it or you don't.”

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