Scientists Find 'Evolutionary Highways' That Guide How Animal Genomes Change

A human, an octopus and a coral look nothing alike, but their chromosomes carry fragments inherited from a common ancestor that lived more than 600 million years ago. Researchers at the University of Vienna have traced how those ancient genomic pieces were reorganized as animal life diversified. The study, published in Science Advances, finds that animal genomes evolve not through unlimited routes but along a restricted set of irreversible pathways the team calls "evolutionary highways."

The researchers examined more than 5,800 available chromosome-scale genomes representing 4,454 species from 19 animal phyla, the largest such comparison across the animal tree of life, the researchers say. To organize the data, they built a framework called "evolutionary genome topology," mapping the variety of animal genome structures onto a single chart. "Understanding these rules of evolution doesn't just tell us about the past," said Oleg Simakov, a professor at the University of Vienna who co-led the study. "It also lets us ask where genome evolution might go next and enables us to identify key measures for the conservation of animal biodiversity."

A major driver of these patterns is a process called "fusion-with-mixing," in which two chromosomes join and their genes become intermixed. Once this happens, the original arrangement cannot be restored, leaving a lasting genomic record. Differences in chromosome numbers between animal groups arise as ancestral chromosomes combine or separate, pushing lineages into distinct regions of what the team calls "genome-architecture space." "For the first time, we can see thousands of genomes on a single map and trace the unique paths along which animals' DNA evolved," said Darrin Schultz, who led the work as a postdoctoral researcher at the University of Vienna and is now an assistant professor at Lehigh University.

Some animal groups occupy isolated parts of the map because their chromosome architecture has few close parallels. Mosquitoes, glass sponges and earthworms are among the lineages that stand out, the researchers say.