Study shows that tiny Tarsiers are our evolutionary cousins

The size of a mouse, with massive eyes and a taste for meat, tarsiers are unusual animals. They are also our remote cousins, according to a new study in the journal Nature Communications.

In the study, researchers at Washington University School of Medicine in St. Louis sequenced and reviewed the tarsier genome. The team concluded that tarsiers are on an essential branch of the primate evolutionary tree – on the same branch as monkeys, great apes, and humans.

“We sequenced the tarsier not only to determine where they fit in primate evolution, but because their physiology, anatomy, and feeding behavior are very unique,” study author Wesley Warren, an associate professor of genetics at the school, said in a news release.

The place of tarsiers among primates has been a source of contention. Their teeth and jaws are more like that of “wet-nosed” primates such as lemurs, but their eyes and noses are like those of “dry-nosed” primates, including monkeys and humans.

By sequencing the entire genome of a tarsier, the study team put tarsiers squarely in the dry-nosed category.

The scientists reviewed genetic sequences referred to as transposons, or “jumping genes,” which can leap from one section of the genome to a different section, often replicating themselves in the process. Over time, transposons lose the capacity to jump. Newer transposons can leap into older transposons, but not the other way around. By examining which transposons were set into others, the scientists could figure out when certain families of transposons lost the capability to jump and thus date the various groups of transposons.

The scientists examined the transposon families of tarsiers, wet-nosed primates and dry-nosed primates, including humans. Tarsiers shared newer transposon families with humans, and just the oldest ones with wet-nosed primates, suggesting that tarsiers belong with us.

Finding Shifting Genes

By contrasting gene sequences from tarsiers with those found in other primates, the scientists discovered 192 genes that are shifting quicker or slower than what is taking place in other primates. These genes probably are associated with the tarsiers’ strange traits, the researchers said.

The team also looked at scientific literature to identify human diseases linked with those genes and discovered 47 diseases. Approximately a quarter were associated with vision and a different 25 percent were linked to musculoskeletal complications.

“The tarsier genes that display unique alterations can give us a clue into human diseases involving the same genes,” Warren said. “If an amino acid has been uniquely changed and it is putatively associated with the tarsier’s novel musculature, maybe it’s an important part of the protein and worthy of a closer look when linked to human disease.”

The researchers said they’d like to get DNA from various tarsier species and populations to assess the health of the tarsier population and conduct other studies.

“If we can sequence the genome of other tarsiers, we can measure the population diversity. A population with a greater amount of diversity should be more capable of surviving changes in its environment,” Warren said. “It will help us determine how endangered they really are so we can implement measures to better protect them.”

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Image credit: Thinkstock

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