Even the shaggy giants were sometimes particularly "hot": Like elephant bulls, male woolly mammoths went through annual phases with increased sex drive and increased aggressiveness, researchers report. This is evidenced by traces of surges in the male sex hormone testosterone in a 33,000-year-old mammoth tusk and in comparative material from a bull elephant. The study results also illustrate the further potential of hormone detection in teeth for research, say the scientists.
They are the famous symbolic animals of the Ice Age: the woolly mammoths (Mammuthus primigenius) were the cold-adapted relatives of today's elephants. They once roamed the steppes of Eurasia in large herds, but then they disappeared more and more until the last remaining populations died out in Siberia about 4000 years ago. The physique of the woolly mammoth is known in detail from finds preserved in the permafrost, and fossil genomes have already provided interesting insights into the characteristics of these animals. One can only speculate about their behavior.
So far it has also remained unclear whether mammoth bulls go through an annual phase that is typical for the representatives of the proboscidea that still exist today: a so-called musth. This is a period of increased sex drive and aggressive behavior. It is known that musth in African and Asian elephants is triggered by surges in the male sex hormone testosterone after the onset of sexual maturity. These concentration increases have so far been detected in them by blood and urine tests. As far as their extinct relatives are concerned, however, there was only indirect evidence of hormone-controlled behavior: signs of injury or broken tusk tips could have been caused by rival fights during musth episodes.
On the trail of hormone-controlled behavior
As part of their study, the researchers led by Michael Cherney from the University of Michigan in Ann Arbor have now investigated the extent to which the hormone surges typical of musth can be detected in the tusks of elephants and their Ice Age cousins. Her focus was on possible traces of testosterone in the so-called dentin - a tooth substance that is continuously deposited in fine layers.
The team used tusks from a male and a female woolly mammoth found in the permafrost of Siberia as the material to be examined. The researchers also examined the tusk of an adult African bull elephant. In order to uncover the growth layers of the dentin, the researchers subjected the tooth materials to an examination using computed tomography. They then took sample material from the identified layers by drilling fine holes. It was then analyzed using mass spectrometric methods to detect traces of hormones.
Successful proof with further potential
As the scientists report, they were actually able to detect traces of testosterone in the tooth materials. In the case of the elephant bull, there were periodic increases in hormone concentration by a factor of 20 in the years after reaching sexual maturity. It thus reflected the musth episodes in the life course of the animal. The scientists then found exactly this pattern in the case of the tusk of the mammoth bull. They attribute the slightly lower values to degradation processes in the material, which is more than 33,000 years old.
In the case of the female mammoth's teeth, on the other hand, the team found only a low level of testosterone, which was also hardly subject to fluctuations. "The temporal patterns of testosterone preserved in the fossil tusks thus provide evidence that adult mammoth bulls, like modern elephants, have undergone periods of musth," Cherney concludes. In terms of duration, periodicity and hormonal activity, the mammoth musth also appeared to be similar to its modern-day elephant counterpart, the scientists say.
According to them, however, the importance of the study results goes well beyond the insight into the reproductive behavior of proboscidea - they could be groundbreaking for research, say Cherney and his colleagues. Because, as the team emphasizes, their method is obviously not only suitable in the case of huge tusks and other hormones can also be detected. "With reliable results on samples as small as five milligrams of dentin, this method could also be used to study animals with smaller teeth, including humans and other hominids," the authors write. "Hormonal traces in modern and ancient dentine offer new approaches to the study of reproductive ecology, life history, population dynamics, diseases and behavior in modern and prehistoric contexts," say the scientists.
Source: University of Michigan, professional article: Nature, doi: 10.1038/s41586-023-06020-9