Did Inbreeding Drive Woolly Mammoths To Extinction?

Lawrence LeBlond for redOrbit.com – Your Universe Online

Much of what we know about the Mammoth may be challenged after new research from a Dutch team has found evidence that the massive mammal may have driven itself to extinction due to inbreeding.

The evidence comes from an unusual feature found in some mammoth fossils taken from the North Sea. This unusual feature suggested to the research team, led by paleontologist Jelle Ruemer of the Natural History Museum Rotterdam, the Netherlands, that inbreeding was largely present in at least some mammoth populations. It is this inbreeding nature that could have forced the Ice Age animal to fall by the wayside some 10,000 years ago.

“The strange feature in question is a round, flat area that researchers were surprised to find on a mammoth neck vertebra from the North Sea. This meant that the neck bone once had a small rib attached to it, a rare abnormality that can point to other skeletal problems,” wrote Science Magazine’s Beth Skwarecki.

In humans, 90 percent of individuals who have similar neck ribs – also known as cervical ribs – die before they reach adulthood, not because of the rib itself, but because the condition occurs alongside other developmental problems. Neck bones may be fused together and bones in the lower back may fail to solidify. This condition is also associated with chromosome abnormalities and cancer, according to a 2006 study published in the journal Evolution.

These neck ribs were found to be about 10 times more common in mammoths from the Late Pleistocene than they are in elephants alive today, according to the new study, published in the journal PeerJ.

The finding peaked Reumer’s curiosity and he and his colleagues combed through local museum collections looking for more evidence in mammoth neck bones also taken from the North Sea. The team found the abnormalities in three of nine cases.

“This seemed [to be] an extremely high incidence,” Reumer said in a statement, noting that a similar search among modern-day elephant bones in museums revealed that only one out of 21 individuals had a neck rib.

“Cervical ribs indicate there has been a disturbance of early pregnancy,” says paleontologist Frietson Galis of the Naturalis Biodiversity Center in Leiden, the Netherlands, who worked with Reumer on the analysis.

A neck rib could be a sign that the mother suffered harsh conditions, like famine or disease, during pregnancy, or it could be a genetic mutation as a result of inbreeding. In the case of mammoths, the researchers believe both scenarios could be at play.

Reumer explained that the extinction of mammoths likely occurred as a result of two incidences. First, climate change fragmented the mammals’ habitat, separating animals into smaller population pockets. Secondly, because of the smaller populations, the mammoths were forced to inbreed. A loss of genetic variation left the animals with few defenses against the onslaught of parasites, disease and human hunting.

Galis describes this vicious cycle as the “extinction vortex.”

“A combination of inbreeding and harsh conditions may be the most likely explanation for the extremely high incidence of cervical ribs,” the research team said, as cited by the LA Times. The animals’ vulnerability “may well have contributed to the eventual extinction of the woolly mammoths.”

The findings by Reumer and his colleagues fits well with research conducted by Eleftheria Palkopoulou, a geneticist who has analyzed mammoth DNA but was not involved in the new study. She said that genetic analysis could determine if inbreeding was truly occurring in mammoth populations that began to shrink starting around 20,000 years ago.

Daniel Fisher, a paleontologist with the University of Michigan, told LA Times that he is skeptical of the new findings.

He noted that the study included only a small number of mammoths and that inbreeding may be the result of an already dwindling population rather than a cause for extinction. He does acknowledge, however, that “there’s no question that [the neck rib] represents some interesting natural history.”

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