Graphic depicting how trio binning produces parent species genomes from F1 hybrids with an evolutionary timescale on the left.
Credit: Dr. William Murphy, Texas A&M University, and colleagues
Researchers at the Texas A&M School of Veterinary Medicine & Biomedical Sciences (VMBS) and an interdisciplinary team of collaborators have uncovered new information about the history of cat evolution explaining how cats—including well-known species like lions, tigers, and domestic cats—evolved into different species, and shedding light on how different genetic changes in cats relate to survival abilities like the ability to smell prey.
By comparing genomes of several cat species, the project, published today in Nature Genetics, has helped researchers understand why cat genomes tend to have fewer complex genetic variations (such as rearrangements of DNA segments) than other mammal groups, like primates. It also revealed new insights into which parts of cat DNA are most likely to evolve rapidly and how they play a role in species differentiation.
"Our goal was to better understand how cats evolved and the genetic basis of the trait differences between cat species," said Dr. Bill Murphy, a VMBS professor of veterinary integrative biosciences who specializes in cat evolution. "We wanted to take advantage of some new technologies that allow us to create more complete cat genomic maps.
"Our findings will open doors for people studying feline diseases, behavior, and conservation," he said. "They'll be working with a more complete understanding of the genetic differences that make each type of cat unique."
Variations on a theme
Among the things the scientists were trying to better understand is why feline chromosomes—cellular structures containing the genetic information for traits like fur color, size, and sensory abilities—are more stable than in other mammal groups.
"We've known for a while now that cat chromosomes across species are very similar to each other," Murphy said. "For example, the chromosomes of lions and domestic cats hardly differ at all. There appear to be far fewer duplications, rearrangements, and other types of variation than what are commonly found in great apes."
In the primate order, this kind of genetic variation has led to the evolution of different species—including humans and great apes.
"The great ape genomes tend to break and rearrange, and even human genomes have very unstable regions," Murphy said. "These variations may predispose certain individuals to have genetic conditions, like autism and other neurological disorders."
The key to this variation between cats and apes, as Murphy found out, appears to be the frequency of something called segmental duplications—segments of DNA that are highly similar copies of other DNA segments found elsewhere in the genome.
"Primate genome researchers have been able to link these segmental duplications to chromosome rearrangements," he said. The more segmental duplications you have in your DNA, the more likely the chromosomes are to rearrange, and so on.
"What we discovered by comparing a large number of cat species genomes is that cats have just a fraction of the segmental duplications found in other mammal groups—primates actually have seven times more of these duplications than cats. That's a big difference, and now we believe we understand why cat genomes are more stable," he said.
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