Male woolly mammoths had hormone-fueled bouts of aggression
Paleoendocrinologists unveiled new details on a testosterone-surge called musth.
There is truly no shortage of interesting courting and mating rituals throughout the animal kingdom. From trilobites “jousting” to win mates to the important pee sniffing rituals of giraffes, getting it on is serious business. And so is winning over a mate.
[Related: Male California sea lions have gotten bigger and better at fighting.]
For the first time, scientists have found direct evidence that adult male woolly mammoths experienced an event called musth. Musth comes from the Hindi and Urdu word for intoxicated, and in the case of giant mammals like adult elephants, this is a testosterone-fueled event where the male sex hormone surges and aggression against rival males is heightened.
The study, published online May 3 in the journal Nature, found evidence that testosterone levels are recorded within the growth layers of both elephant and mammoth tusks. In living male elephants, blood and urine tests recognized the elevated testosterone, but musth battles from its extinct relatives has only been inferred from to fossilized consequences of testosterone-fueled battle, such as pieces of tusk tips and skeletal injuries.
In the study, an international team of researchers report the presence of annually recurring testosterone surges (up to 10 times higher than baseline levels) are present within a permafrost-preserved woolly mammoth tusk.
The team sampled tusks from one adult African bull elephant from Botswana and two adult woolly mammoths: a male who roamed Siberia over 33,000 years ago and a roughly 5,597 year-old female that was discovered on Wrangel Island. This Arctic Ocean island used to be connected to northeast Siberia and is the last place where woolly mammoths survived up until about 4,000 years ago.
“This study establishes dentin as a useful repository for some hormones and sets the stage for further advances in the developing field of paleoendocrinology,” study co-author and paleontologist at the University of Michigan Museum of Paleontology Michael Cherney said in a statement. “In addition to broad applications in zoology and paleontology, tooth-hormone records could support medical, forensic and archaeological studies.”
Hormones are signaling molecules that help regulate physiology and behavior. Testosterone in male vertebrates is part of the steroid group of hormones. Testosterone circulates throughout the bloodstream and accumulates in various tissues.
[Related: How much acid should you give an elephant? These scientists learned the hard way.]
According the authors, their findings demonstrate that steroid records in teeth can provide scientists with meaningful biological information that can even persist for thousands of years.
“Tusks hold particular promise for reconstructing aspects of mammoth life history because they preserve a record of growth in layers of dentin that form throughout an individual’s life,” study co-author and U-M Museum of Paleontology curator Daniel Fisher said in a statement. “Because musth is associated with dramatically elevated testosterone in modern elephants, it provides a starting point for assessing the feasibility of using hormones preserved in tusk growth records to investigate temporal changes in endocrine physiology.”
They team used CT scans to find the annual growth increments deep within the tusks, like tree rings. Modern elephant and ancient mammoth tusks are elongated upper incisor teeth, and only hold on to traces of testosterone and other steroid hormones. The chemical compounds are all incorporated into dentin, which is the mineralized tissue that makes up the interior portion of teeth.
The study also required new methods to extract steroids from the tusk dentin with a mass spectrometer. Mass spectrometers identify chemical substances by sorting the ions present by their mass and charge.
“We had developed steroid mass spectrometry methods for human blood and saliva samples, and we have used them extensively for clinical research studies. But never in a million years did I imagine that we would be using these techniques to explore ‘paleoendocrinology,'” study co-author and U-M endocrinologist Rich Auchus said in a statement.
The results and the new measuring technique will likely further new approaches to investigating reproductive endocrinology, life history, and even disease patterns in modern and prehistoric context.