Infinite Fertility. That is one of the aspects that distinguishes female naked mole rats from humans and other mammals, write American and Canadian biologists in Nature Communications. It is known in humans, including mice, that fertility is related to the finite amount of egg cells that are produced in female embryos before birth. But in the naked mole rat, this so-called oogenesis only takes place after birth, in extremely high numbers. The eggs produced are also of very good quality.
The naked mole rat (Heterocephalus glaber) is a rodent species from eastern Africa that lives in large, underground colonies. As their name implies, the animals have no body hair and extremely large front teeth, which they use when digging tunnels. At the head of each colony is a queen: the only one who bears babies, and does so for the rest of her life. (The only other mammal to maintain such a eusocial, insect-like hierarchy is the Damaraland mole rat of southern Africa.)
This continuous reproduction is striking, because the life of naked mole rats is much longer than that of other rodents. A queen gives birth to up to five litters per year, with about thirteen offspring at a time. That means she can have more than 2,000 children in her lifetime.
Struggle for succession to the throne
It has long been known that a six-month-old naked mole-rat queen has an egg reserve ten times that of other mammals of the same age and size. But only now the exact oogenesis process has been unravelled. For example, it turns out that all female naked mole rats have stem cells that can develop into eggs, but that in practice this only happens with the queen. The initial stem cell stock is also much larger than in other rodents: eight days after birth there are already about 1.5 million. In the queen, oogenesis takes place in the following months, but stem cells also remain for later egg development – they were found in the body of a six-year-old queen, for example.
To test what happens if the queen dies, the biologists removed several three-year-old subordinate females from the colony. If they were placed with a male, the development of their eggs would still start. In contrast to bees, which may or may not be born as a queen, any female naked mole rat can become a queen. When their predecessor dies, the females compete among themselves for succession to the throne.
What makes naked mole rat eggs extra special is that they remain of high quality – human eggs deteriorate as they age.
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