Testosterone preserved in the tusks of male woolly mammoths reveal that they went through a seasonal change called musth, just like modern elephants do.
Once they reach sexual maturity, male African and Asian elephants go through musth for about three months every year. The shift is marked by a surge in testosterone and is often accompanied by thick, gooey secretions from ducts on the elephants’ temples. Male elephants are said to be more aggressive and restless during this time, although the exact relationship between the hormonal changes and behaviour is unclear.
Woolly mammoths (Mammuthus primigenius), which went extinct about 4000 years ago, were closely related to Asian elephants. Their tusks, like those of elephants, grew throughout their lives, and previous studies have recorded hormones such as cortisol, testosterone and progesterone preserved in a tooth tissue called dentine.
Palaeontologists have long suspected that woolly mammoths experienced musth. To test this idea, Michael Cherney at the University of Michigan and his colleagues isolated and analysed testosterone levels in tusks from a male African elephant, a male woolly mammoth estimated to have lived about 35,000 years ago and a female woolly mammoth thought to have lived around 5500 years ago. By sampling many sections along the length of a tusk, they were able to see how the hormone levels fluctuated over the animals’ lifetimes.
In the elephant, testosterone levels peaked at 20 times higher during musth than the rest of the year. The tests showed similar fluctuations in the male mammoth, with testosterone reaching 10 times higher than baseline. There was little variation in testosterone levels in the female mammoth.
“This is such an exciting and fascinating piece of scientific sleuthing,” says Susan Alberts at Duke University in Durham, North Carolina, who wasn’t involved in the study. “The comparison of the elephant and mammoth tusks is compelling evidence that they are picking up the same signals in the two species.”
Musth was “low-hanging fruit” for an initial study, Cherney says, but the new method has the potential to document many aspects of the lives of mammoths, as well as other extinct animals. “We anticipate being able to identify pregnancies, maturation ages, stress events and other things that could be used to improve our understanding of mammoth and mastodon palaeobiology,” he says.