| Mandarina: A Microcosm of Biodiversity |
| Studies of island organisms have shown that diverse radiations within phylogenetically
close groups of organisms have occurred in isolated oceanic islands. The
island endemics provide excellent natural laboratories in which we can
test models for speciation, adaptive radiation and processes of diversification.
The land snail genus Mandarina of the Ogasawara Islands is an excellent model system for studying origins
of biological diversity and evolutionary processes. |
 Mandarina aureola |
| The Ogasawara Islands are located in the north-west Pacific, about 1000 km south of Japan, and they consist of about 30 small volcanic islands. The biggest island among them is only 24 km2 in area. The climate of islands is subtropical with temperature
ranging from an average of 18C in winter to 25C in summer. The Ogasawara
Islands have been entirely isolated from other regions, and the biota of
these islands (plants, birds, insects and land snails) are characterized
by several peculiarities as are the biota in other oceanic islands. For
example, approximately 75% of the native tree species in the islands are
considered endemic(Kitayama 1991). There were at least four endemic species of birds, three of which have
been already extinct. There are no native mammals except for the endemic
Bonin fruit bat. |
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| Dendrocacalia crepidifolia (Nakai): an endemic genus of woody sunflower family. | A view from the highest mountain (Mt. Chibusa, approxiately 400m above
sea level) in Ogasawara. |
| More than 100 species of land snails have been described in Ogasawara since
the 19th century, and approximately 90% of these species are endemic.
In addition, several genera such as Mandarina and Hirasea have undergone extensive adaptive radiation within the islands. Although
most of the species of Hirasea became extinct, all of the species of Mandarina described in the 19th-early 20th century still survive. The natural histories of individual populations,
community structures, the history of radiation, and the process of speciation
of Mandarina have been studied intensively in the last 10 years. By reviewing recent
studies on Mandarina, I show here how these unique land snails can provide important insights
into the nature of speciation and contribute to understand evolutionary
processes. |
 Mandarina hahajimana |
 Mandarina polita |
1. Adaptive Radiation in Mandarina.
2. Character Displacement, Reproductive Isolation, and Hyridization.
3. Fossil Records and Discontinuous Evolution.
4. Recent Extinctions and Conservation.
5. References
| since: 1 May 2003 produced by Satoshi Chiba Lab. site admin / S. Chiba |