A research team led by Associate Professor Shoji Hayashi of the Dinosaur Department at Okayama University of Science and Associate Professor Mugino Kubo of the Graduate School of Frontier Sciences at the University of Tokyo has revealed for the first time that the Amami rabbit, a special natural monument that inhabits the Ryukyu Islands, grows slowly, taking about five times longer than closely related rabbits.
In this study, bone histology was performed on the limb bones of Amami rabbits, and it was discovered that growth arrest lines, which are said to form once a year, are formed in bone tissues much more frequently than in hares. It was found that while common rabbits that live on the Japanese mainland and other continents reach maturity within a year, Amami rabbits are likely to reach maturity in nearly five years.
This kind of extreme growth delay in mammals has been known in extinct fossil species that once lived on islands, but this is the first discovery of a living species. In the special environment of an island, with few predators and limited food resources, it is known that animals tend to "carefully raise a small number of young" rather than giving birth and dying in large numbers, suggesting that the Amami rabbit may have evolved an extremely slow life cycle. On the other hand, the significantly longer period it takes to mature could lead to a decrease in reproductive numbers and difficulties in maintaining the population, increasing the risk of extinction.
Analysis of bone tissue also revealed that the Amami rabbit's bone structure is much denser and stronger than that of closely related species, a specialized structure that is thought to have evolved to adapt to island life, including climbing and descending steep terrain.
The results of this study not only deepen our understanding of the special ecology and evolutionary characteristics of animals endemic to the Ryukyu Islands, but also demonstrate that the use of bone histology techniques can provide valuable insights into the life cycles of rare animals for which ecological monitoring surveys are difficult.
Paper information:[Mammal Study] Bone histology reveals the slow life history and skeletal adaptations of the Amami rabbit Pentalagus furnessi (Lagomorpha: Mammalia)
