Naked mole-rats: Not a mole, not a rat, and not an African mole-rat

You may remember him from the Saturday morning cartoon, Kim Possible – Rufus, the naked mole-rat, tenacious pet of Kim’s best friend Ron. With very little hair, some whiskers, wrinkly-pink skin and large teeth, Rufus stole the hearts of all who watched him save the day. In many episodes, Rufus is the hero, and like Kim and Ron, scientists agree that naked mole-rats are pretty cool.

In fact, zoologists at The Field Museum have determined that they are so unique that they deserve to be classified in a family of their own.  Prior to this, they were previously classified with other African mole-rats.

“Our realization that naked mole-rats were worth looking into came about during a DNA analysis of evolutionary relationships among the South American forms,” said Bruce Patterson, MacArthur Curator of Mammals at The Field Museum.

In the first study of its scope, Patterson and graduate student Nate Upham (now a Field Museum Research Associate and post-doc at McMaster University in Hamilton, Canada) justified putting naked mole-rats in a family of their own by comparing DNA, fossils, and characteristics listed in scientific literature.

The team began their analysis by examining mitochondrial and nuclear DNA sequences from 200 species representing all lineages of this group, generated in The Field Museum’s Pritzker Lab and other labs in Canada and Brazil. Mitochondrial sequences tend to be fast-evolving and informative about recent evolutionary splits, while nuclear genes tend to evolve more slowly and shed light on more ancient divergence events.  By sequencing both classes of DNA, the researchers could recover and resolve the group’s entire history.

Next, the scientists used 22 well-studied fossils to calibrate this set of branches on the rodent tree of life.

“Fossils allow researchers to establish the timing of various branching points on the tree by setting a minimum date for the appearance of a particular lineage,” said Upham. They noted that the naked mole-rat (Heterocephalus) had diverged from other African mole-rats (Bathyergidae) about 31 Mya in the early Oligocene.

Finally, Patterson and Upham read up on the subject. Because naked mole-rats have been studied extensively for their extraordinary longevity and resistance to cancer, much has been written about them. This enabled the researchers to review the literature and note all sorts of differences that evolved after their separation from African mole-rats, which justified placing them off in a family of their own.

Classifications convey information about how different things are. By separating the naked-mole rats into their own family, scientists will be able to better understand its biology and evolutionary history relative to other African mole-rats.