Research press release




ケナガマンモスの生殖生理と行動の多くの特徴、例えば、成体の雄ゾウの場合と同様にテストステロン濃度の上昇を伴い、生殖の成功に関連する発情期があったのかどうかといったことは判明していない。牙を形成する骨性物質である象牙質の層には成長記録が保存されており、マンモスの生活史の詳細を復元するために利用できるため、牙は重要な情報源になっている。今回、Michael Cherneyらは、この記録の潜在的価値を評価するため、現生アフリカゾウと、3万8866~3万3291年前に生息していたと推定される雄のケナガマンモスと、5885~5597年前に生息していたと推定される雌のケナガマンモスの牙を調べて、ホルモン濃度の変動の特徴を探索した。



Male woolly mammoths underwent musth, testosterone-driven changes associated with the mating season, just as their modern elephant relatives do, a study published in Nature suggests. Hormone fluctuations are identified in the dentin of a male mammoth tusk estimated to be approximately 39,000–33,000 years old. The findings demonstrate the value of analysing hormone levels in teeth (including protruding tusks) to investigate hormone-driven behaviours in ancient and modern animals.

Many features of woolly mammoth reproductive physiology and behaviour are unknown, such as whether they underwent musth episodes — periods of elevated testosterone associated with reproductive success in adult male elephants. Tusks are a promising source of information as they preserve a record of growth in layers of a bony material called dentin, which can be used to reconstruct details of mammoth life histories. To assess the potential value of this record, Michael Cherney and colleagues searched for signatures of hormone fluctuations in the tusks of a modern African elephant, a male woolly mammoth (estimated to have lived 38,866 to 33,291 years ago) and a female woolly mammoth (estimated to have lived 5,885 to 5,597 years ago).

In the African elephant, the analyses demonstrate that the male experienced increases in testosterone levels during adult life, but not in its younger years, consistent with periods of musth during mating seasons. Such increases were up to 20 times higher than testosterone levels at other points in the year. Samples from the male woolly mammoth tusk reveal similar fluctuations in testosterone during adult life, although the increases were lower (around 10 times higher than other periods) than that of the African elephant. These lower hormone levels in the male woolly mammoth may be a result of sample degradation, the authors suggest. In the female woolly mammoth, testosterone (as well as progesterone and androstenedione) levels were lower than in the male mammoth and elephant, and testosterone in the female showed very little variation.

These findings represent the first endocrinological evidence that woolly mammoths experienced musth, the authors report. The research also demonstrates the potential of dental growth records to reveal hormonal changes associated with life-history events, the authors conclude.

doi: 10.1038/s41586-023-06020-9

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