The cataclysmic asteroid impact 66 million years ago spelled the end for non-avian dinosaurs while marking the dawn of a new chapter in the evolution of birds.
A recent study by the University of Michigan delves into the genomic changes in birds that were catalyzed by the end-Cretaceous mass extinction event, illuminating the crucial role of these changes in the remarkable diversity of modern bird species.
The research unravels the genetic imprints that delineate the evolutionary journey of birds into over 10,000 distinct species, providing compelling insights into their remarkable resilience and adaptability.
“By studying the DNA of living birds, we can try to detect patterns of genetic sequences that changed just after one of the most important events in Earth’s history,” said lead author Jake Berv, who completed the study as a Michigan Life Sciences Fellow in the U-M Department of Ecology and Evolutionary Biology. “The signature of those events seems to have imprinted into the genomes of the survivors in a way that we can detect tens of millions of years later.”
The genetic code of living organisms consists of four nucleotide molecules: A, T, G, and C. The arrangement of these nucleotides in a genome defines the “blueprint” of life. As the DNA code evolves, the overall composition of DNA nucleotides across the genome can shift, impacting genetic variation and contributing to an organism’s evolutionary potential.
Researchers have discovered that mass extinction events triggered shifts in nucleotide composition, which appear to be linked to the developmental processes, adult size, and metabolism of birds.
The surviving bird species underwent significant changes within 3 to 5 million years after the mass extinction. One notable change was the development of smaller body sizes. Additionally, more bird species became “altricial,” meaning they hatched in a more embryonic state, requiring parental care and taking weeks to fledge. This contrasts with “precocial” birds like chickens and turkeys, which hatch ready to fend for themselves.
“We found that adult body size and patterns of pre-hatching development are two important features of bird biology we can link to the genetic changes we’re detecting,” said Berv, now a Schmidt AI in Science postdoctoral fellow with U-M’s Michigan Institute for Data & AI in Society.
Berv highlights the complex challenge of unraveling the interrelations among major bird groups in evolutionary biology and ornithology. Determining the tree of life for living birds has proven to be a formidable task. With the advancement of research over the past 15 years, scientists have increasingly utilized extensive genomic data sets to tackle this issue.
In the past, researchers employed genomic data to investigate the evolution of birds‘ genomes using statistical models with rigid assumptions. While these “traditional” models enabled the reconstruction of genetic change history, they often assumed that the composition of DNA, particularly its proportion of A, T, G, and C nucleotides, remained constant throughout evolutionary history.
In late 2019, Berv collaborated with Stephen Smith, U-M professor of ecology and evolutionary biology, who was developing a groundbreaking software tool to closely track DNA composition over time and across various branches of the tree of life. This innovative tool allowed researchers to challenge the traditional assumption that DNA composition remains constant, enabling the model of DNA evolution to vary across the evolutionary tree and identify significant shifts in DNA composition.
In their latest research, these shifts were observed to occur within about 5 million years of the end-Cretaceous mass extinction, according to Berv. Their pioneering approach also facilitated the estimation of which bird traits were most closely associated with these shifts in DNA composition.
“This is an important type of genetic change that we think we can link to the mass extinction event,” he said. “As far as we know, changes in DNA composition have not been previously associated with the end-Cretaceous mass extinction in such a clear way.”
Daniel Field, a renowned vertebrate paleontology professor at the University of Cambridge, has delved into understanding the impact of the end-Cretaceous mass extinction on bird evolution. His guidance has been pivotal in unraveling the mysteries of early bird evolution post-extinction.
“We know that mass extinction events can dramatically affect biodiversity, ecology, and organismal form. Our study emphasizes that these extinction events can actually influence organismal biology even more profoundly – by altering important aspects of how genomes evolve,” Field said. “This work furthers our understanding of the dramatic biological impacts of mass extinction events and highlights that the mass extinction that wiped out the giant dinosaurs was one of the most biologically impactful events in the entire history of our planet.”
The researchers’ daring approach of challenging standard assumptions in evolutionary biology is leading to a richer understanding of the intricate sequence of events in the early history of birds.
“We have typically not looked at the change in DNA composition and model across the tree of life as a change that something interesting has happened at a particular point of time and place,” Smith said. “This study illustrates that we have probably been missing something.”
Journal reference:
- Jacob S. Berv, Sonal Singhal, Daniel J. Field, Nathanael Walker-Hale, Sean W. McHugh, J. Ryan Shipley, Eliot T. Miller, Rebecca T. Kimball, Edward L. Braun, Alex Dornburg, C. Tomomi Parins-Fukuchi, Richard O. Prum, Benjamin M. Winger, Matt Friedman, Stephen A. Smith. Genome and life-history evolution link bird diversification to the end-Cretaceous mass extinction. Science Advances, 2024; DOI: 10.1126/sciadv.adp0114