Differential geographic patterns of mitochondrial DNA variation in two sympatric species of Japanese wood mice, Apodemus speciosus and A. argenteus

Abstract

We examined the gene sequences of mitochondrial cytochrome b (cyt b ) in two Japanese wood mouse species, Apodemus speciosus (n = 89) and A. argenteus (n = 46), which are distributed on the four main islands of Japan (Hokkaido, Honshu, Shikoku, and Kyushu) and on the small islands surrounding them. Apodemus speciosus , the larger of the two species, showed substantial genetic variation, with a maximum of 3% sequence divergence, and remarkable phylogenetic subdivision with two major clades. One clade represents haplotypes from a central region, including Honshu, Shikoku, Kyushu, and their adjacent islands; the other clade includes haplotypes from Hokkaido and the peripheral islands, forming four subclades: a) Hokkaido, b) Sado Island, c) Satsunan Islands, and d) the Izu Islands. Sequence divergence among the four subclades was 1.0 to 1.5%, implying that A. speciosus colonized these geographic regions 0.2 to 0.3 million years ago, assuming a substitution rate of 2.4% per million years. The population on the Izu Islands has preserved haplotypes that are distinct from those in any other region, providing good evidence for the natural colonization of the volcanic islands of the Izu Islands. The cyt b sequence variation had no relation to the karyotypic dimorphism for the eastern (2n = 48) and western (2n = 46) geographic groups, between which a strict border exists at central Honshu. On the other hand, Apodemus argenteus , the smaller of the two species, showed a similar level of sequence divergence (maximum of 3%) but no substantial geographic differentiation: populations in Hokkaido, Sado, and Yakushima shared similar haplotypes with each of the central populations, suggesting that genetic exchanges occurred among the localities in the last 0.15 million years. The apparent genetic structure of the mitochondrial DNA found in the A. speciosus population might be caused solely by longterm existence in insular regions, presumably due to ecological superiority relative to A. argenteus .

Mitochondrial Phylogeography and Population History of the Large Japanese Wood Mouse (Apodemus speciosus) on Sado Island, Japan

“…However, the estimated timings of these colonizations are debatable and vary among taxa. Conversely, some mammals such as A. argenteus (Suzuki et al 2004), hares (<20 ka; Nunome et al unpublished data), and voles (Microtus montebelli; Tomida personal communication) showed less mitochondrial sequence divergence. These observations suggest that several opportunities to colonize the island took place, or that artificial introductions were made of some mammal species now on Sado Island.…”

“…We determined the Cyt b gene sequences (1,140 bp) using the method described by Suzuki et al (2004). Sequences were resolved on a 3100 Genetic Analyzer (Applied Biosystems) and assembled into a single consensus sequence with the aid of PROSEQ software (Filatov 2002).…”

“…Phylogeographic analyses covering the entire species range showed that some groups of small island populations (including Sado Island) harbor a reciprocally monophyletic mitochondrial lineage (Suzuki et al 2004). Our previous study based on a nuclear gene in combination with mitochondrial genes revealed a strong association between the phylogeographic structure and the connection-separation events among the islands as well as demographic fluctuation during the Quaternary glacial cycles (Tomozawa and Suzuki 2008).…”

Prenatal postcranial development in two species of sympatric Japanese wood mice (<i>Apodemus argenteus</i> and <i>A. speciosus</i>): a comparison of arboreal versus terrestrial congeners

“…The two species are both distributed widely in Japanese archipelago and often found sympatrically in forest habitat. Based on molecular evidence, the divergence time is estimated around five or six million years ago [18, 22, 23]. The large Japanese wood mouse, A. speciosus , is found throughout the four main islands and their peripheral islands, including Sado Island, the Izu Islands and the Satsunan Islands [23].…”

Phylogenetic Relationships and Relictualism of Rock-Crawlers (Grylloblattodea: Grylloblattidae) in Cave and Mountain Habitats of Korea

“…Other molecular studies have found evidence of genetic subdivision between populations, but genetic divergence was between clades inhabiting northern Japan and southern Japan and Korea. These include taxa as diverse as plants (Senni et al 2005, Ikeda et al 2006, termites (Park et al 2006), and rodents (Iwasa et al 2002, Suzuki et al 2004, Terashima et al 2006. Only two studies provide evidence of deep genetic divergence between Korea and Japan: one study focusing on ßightless carabid beetles (Tominaga et al 2000) and the other study on the chrysomelid beetle Plateumaris shirahatai Kimoto (Sota and Hayashi 2007).…”