Ecological diversity and speciation in land snails of the genus Mandarina from the Bonin Islands

Abstract

Endemic land snails of the genus Mandarina of the oceanic Bonin Islands offer an example of habitat and character divergence among closely related species. The molecular phylogenies of Mandarina show that a divergence of arboreal, semiarboreal, and ground-dwelling species has occurred repeatedly in different times, areas, and lineages. Ecological diversification is suggested to be important for the coexistence of Mandarina species based on the facts that sympatric species are typically highly differentiated ecologically and morphologically, and that species occupying similar habitats do not coexist. The ecological diversification of Mandarina has occurred without much genetic divergence compared with that of its mainland relatives. This suggests that morphological and ecological diversifications are accelerated in depauperate environments where there are fewer competitors and predators. Although the details of the reproductive isolation mechanisms are not understood and further examination is needed, the rapid evolution of prezygotic isolation is the main cause of speciation in Mandarina. In particular, ecological diversification may be an effective barrier to gene exchange between two species. Because of incomplete postmating isolation and the lower genetic divergence among species of Mandarina, breakdowns of reproductive isolation have frequently occurred as a result of habitat change. It is important to estimate the effect of hybridization on species diversification in future studies.

Mitochondrial DNA divergence in yoshinobori gobies (Rhinogobius species complex) between the Bonin Islands and the Japan–Ryukyu Archipelago

“…However, the Bonin Islands appeared above sea level before the middle Pleistocene (Kaizuka, 1977;Imaizumi and Tamura, 1984), implying that the ancestral populations of endemic organisms in the Bonin Islands reached the islands from elsewhere during the early to middle Pleistocene (ca. 0.9-1.8 million years ago) (Chiba, 2002). If the date (1.8 million years ago) is used as the calibration point of the molecular evolutionary rate, the ND5 gene of Rhinogobius species evolved faster, 3.8% per million years.…”

“…The specimens were deposited in the National Science Museum, Tokyo (catalogue number T he Bonin (Ogasawara) Islands are typical oceanic islands, located in the western Pacific 1000 km south of Tokyo, Japan. They are characterized by many endemic land animals and plants (Ito, 1998;Chiba, 2002), as well as an endemic freshwater goby, Rhinogobius sp. Bonin Island (BI) form (Ogasawara-yoshinobori), distributed on Anijima, Chichijima, and Hahajima Islands (Suzuki, 1992(Suzuki, , 2003Yokoi and Hosoya, 2003).…”

The character of the New Zealand land snail fauna and communities: some evolutionary and ecological perspectives

“…There is some empirical support for this hypothesis from field obervations and laboratory experiments (Cain and Cowie, 1978;Cameron and Cook, 1989;Cowie, 1995). However, there are numerous contradictory examples, such as semi-arboreal and arboreal species that possess shells with a low spire (e.g., Chiba, 2002). Thus, a compelling case for a single ecological dimensionality to the observed dispersion of the spire index has not yet been made.…”

Genetic population structure of a reef goby, Bathygobius cocosensis, in the northwestern Pacific

“…1). They separated from any continental island by [1,000 km and have many endemic land animals and plants (Ito 1998;Chiba 2002). Among the aquatic animals, a freshwater goby (Rhinogobius sp.)…”