University of Michigan scientists used artificial intelligence to identify a striking pattern in the evolution of Passeriformes, the bird order that includes most songbirds. Their analysis suggests that songbirds did not evolve at a constant rate. Instead, major changes in body shape often occurred in rapid evolutionary bursts linked to shifts in Earth’s climate.
Evolutionary theory has long suggested that biodiversity develops through alternating periods of rapid change and slower evolutionary phases. Fossil evidence has supported this idea, but the new study detected the pattern by analyzing skeletal measurements from thousands of modern bird specimens. The researchers found that several major bursts in passerine evolution coincided with significant episodes of global climate change.
Evolutionary Change Occurs in Sudden Bursts
“This is really important for evolutionary theory because there’s a long history, going back 100 years, that predicts the emergence of new groups, called evolutionary radiations, is often associated with an explosive burst of diversification. Evolutionary theory predicts that adaptive radiations may account for a large portion of the diversity of life on Earth,” said Jake Berv, lead author of the study and postdoctoral fellow in the U-M School for Environment and Sustainability.
“This could be because of a new ecological opportunity, or it could be because a group dispersed to a new continent, resulting in dramatic accelerations in their rate of evolution. The idea is that, over time, there’s less opportunity as evolution proceeds, and so it slows down, and that this occurs in pulses across time. That’s what theory predicts, and that seems to be what we see in the data as well.”
The findings were generated using artificial intelligence and a large statistical model. The study was published in Nature Ecology & Evolution and received primary support from Schmidt Sciences and the David and Lucile Packard Foundation.
Artificial Intelligence Measures Thousands of Bird Skeletons
To reconstruct the evolutionary history of passerine birds, the University of Michigan research team, including senior author Brian Weeks, examined more than 2,000 species and compiled more than 170,000 individual skeletal measurements.
This large-scale analysis was made possible by Skelevision, an artificial intelligence tool developed by Weeks’ laboratory in collaboration with David Fouhey’s laboratory at New York University.
Skelevision photographs specimens—in this case, bird skeletons—in front of a measurement grid that provides a consistent scale. During a seven-year collaboration, Weeks and Fouhey developed an AI model that can accurately measure 12 bones throughout a bird’s skeleton.
The researchers used Skelevision to scan and measure more than 15,000 museum specimens, most of which came from the collections of the U-M Museum of Zoology. Each specimen can be scanned in approximately 45 seconds, allowing scientists to digitize and analyze entire museum collections much more efficiently than traditional methods allow.
Reconstructing 45 Million Years of Bird Evolution
Berv also developed a new statistical method called bifrost. The method enabled the team to analyze each bird’s complete skeleton instead of studying individual bones separately. Using this approach, the researchers estimated how passerine body shapes changed over approximately 45 million years of evolution.
“The whole organism is an integrated, complex morphology, and each of the individual pieces is interrelated to every other part in the body,” Berv said. “The question from the model’s perspective is, ‘What is the sequence of evolutionary changes that needs to happen to explain the variation we can see today?'”
The analysis identified a period of particularly rapid body-shape evolution approximately 35 million years ago. This evolutionary burst occurred around the Eocene-Oligocene transition, a major period of global cooling.
The statistical analysis also detected a cluster of evolutionary slowdowns approximately 15 million years ago, coinciding with another important geological event.
“Our findings have definitely shifted my thinking about how the world works,” said Weeks, associate professor of ecosystem science and management at U-M’s School for Environment and Sustainability. “This pattern we found with rare, big increases in the rates of evolution and lots of small decreases in the rate of evolution is really consistent with a pattern where lineages are exploring new ecological space and changing rapidly to take advantage of that opportunity.”
Climate and Geography Influence Evolutionary Rates
The researchers tested their results further by examining the global geographic distribution of the birds included in the study. Their analysis showed that geography also helps predict the average rate of morphological evolution.
Bird communities living at higher latitudes, where seasonal temperature changes are more extreme, tend to include species that evolve faster than species living closer to the equator. Because similar patterns appeared across both deep evolutionary time and modern geographic regions, the findings suggest that environmental variability may play an important role in shaping bird body forms.
“It looks like there’s a connection between latitudinal gradients and rates of morphological evolution that has been underappreciated,” Weeks said. “I hope our findings will inspire a new integration of rates of morphological change into other big areas of interest, things like the very well-known latitudinal gradients in biodiversity.”
AI Reveals New Value in Natural History Museums
The study also underscores the scientific value of natural history museum collections. According to Weeks, artificial intelligence is helping researchers extract data from preserved specimens at a scale that would have been extremely difficult to achieve in the past.
“It’s especially clear how important it is to invest in museums when you think about the scale of an analysis like this; it’s so far beyond the scope of what can be done using specimens contributed by an individual collector,” he said. “It’s also fun to imagine what early collectors would make of how we’re using the specimens they collected — I imagine it would blow their minds to learn that a computer has analyzed a photograph of these specimens. It’s just another example of how impossible it is to foresee the full future value of a specimen.”
What Bird Evolution Can Teach Us About Climate Change
The researchers say their findings may help scientists understand how species could respond to the rapid climate change occurring around the world today.
“Right now, we’re in this moment in human history where there’s dramatic global climate change, and we don’t know what’s going to happen over even a 10-year period, let alone over a 10-million-year period,” Berv said. “To have a chance of understanding the long-term impact of human activity on Earth, we have to study the relationship between events in Earth’s history and evolutionary transitions.”
The research was also supported by the Michigan Institute for Data & AI in Society, the Natural Sciences and Engineering Research Council of Canada, and the National Science Foundation.
Source: www.sciencedaily.com