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Genetic difference in Mt. Fuji mice suggests forest road restricts wildlife movement

This Dec. 16, 2013 file photo shows the Fuji Subaru Line toll road that divides a forest near the fifth station of Mount Fuji. (Mainichi/Toshio Odagiri)

KOFU -- Japanese researchers have found significant genetic differences between mice on either side of a forest road winding up to the fifth station of Japan's iconic Mount Fuji.

    Jun Sato, an associate professor of evolutionary biology at Fukuyama University's Department of Biotechnology in Hiroshima Prefecture, and other researchers studied rodents that inhabit the forest along the Fuji Subaru Line road.

    Genetic differences between the mice suggest the road is preventing the mice from crossing back and forth, meaning they are breeding amongst themselves on each side. The road slicing through the forest is considered especially significant in the differences among small Japanese field mice populations, which often travel along tree branches. Sato pointed to the necessity of installing "animal pathways" over the road so that wildlife can get across it.

    The researchers set traps at 13 locations along the road -- 12 on opposite sides of the same altitude at set intervals, and one at a single location -- at between about 1,200 meters and 2,200 meters above sea level for two to four days in July 2015, August 2016, and again in November 2018. They caught a total of 139 small Japanese field mice, large Japanese field mice and Smith's red-backed voles.

    The largest number of small field mice were caught at about 1,600 meters above sea level. When compared, the mitochondrial DNA of the 19 small field mice revealed significant differences. Comparisons of 35 large field mice -- the largest number of mouse type caught -- which mostly move on the ground and were captured at about 1,500 meters above sea level also revealed genetic differences, though they were not as statistically significant as those in their smaller cousins.

    This photo shows a large Japanese field mouse and a trap set beside the Fuji Subaru Line at about 1,600 meters above sea level on Aug. 25, 2016. (Photo courtesy of Fukuyama University associate professor Jun Sato)

    Mitochondrial DNA is passed down matrilineally.

    "As well as studying more samples, we'd like to analyze paternal genes, too. By doing so, we'd like to further clarify the impact of artificial barriers on the movement of animals," Sato said.

    "Common animals such as mice are local foundation species, eating plants and animals, and being eaten by other animals in turn," said Shusaku Minato, head of the Animal-pathway & Wildlife Association, who participated in the research. "If their lives are threatened, such as being unable to move freely, that affects the whole local ecosystem."

    The Fuji Subaru Line is a toll road on the northern slope of Mount Fuji constructed by Yamanashi Prefecture in 1964. It is about 30 kilometers long, and winds up the mountain to an altitude of about 2,300 meters.

    The study was published in the October 2020 issue of the Mammal Society of Japan's English-language journal, Mammal Study.

    (Japanese original by Shinichi Sariishi, Kofu Bureau)

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