The Japanese wood mouse (
Apodemus speciosus group) is currently. classified into 4 species on the basis of their morphological features, such as
A. speciosus which is composed of
A, s. speciosus and
A. s. sadoensis, A. ainu, A, miyakensis and
A. navigator including
A. n. navigator, A. n. tusimaensis, A. n. dorsalis and
A. n. insperatus. However, this classification system is still a matter of considerable controversy.
The present reports describes results of cytological and biochemical studies on specimens of Japanese wood mouse from 87 different localities in this country with a hope of presenting fundamental data which would contribute to the establishment of a standardized taxonomy in this animal group.
The
A. speciosus group was found to be composed of three subgroups with respect to their chromosome number. Out of 494 animals studied, 233 were found to have 46 chromosomes, 11 had 47 chromosomes and 250 had 48 chromosomes. They were tentatively referred to as 2
n=46 type, 2
n=47 type and 2
n=48 type individuals, respectively. Karyotypeanalysis of these animals revealed that the 2
n=48 type animal possessed two pairs of extra acrocentrics but lacking one pair of submetacentrics, and the 2
n=46 type, the reverse. The 2
n=47 type individuals showed a karyotype intermediate between the previous two. It was considered that this chromosomal variation was due to the Robertsonian conversions based on banding pattern analyses carried out with the use of the trypsin G-banding technique (Fig. 4) .
The survey of geographical distribution of animals belonging to the
A. speciosus group with a special reference to their chromosome number resulted in the detection of a boundary line which ran through the central part of the main land, connecting Toyama with Hamamatsu, and divided this animal group into two, each having a different karyotype. Thus, on the eastern side of the line, involving the eastern part of the main land, Hokkaido, and their adjoining islands, only 2n=48 type animals were found, whereas on the western side including the western part of the mainland, Shikoku, Kyushu and their adjoining islands, only 2
n=46 type individuals were trapped (Fig. 5) .The 2
n=47 type animals were collected only in a very narrow hybrid zone locating on the Toyama-Hamamatsu line. Such an allopatric distribution of the
A. speciosus group suggests strongly that this group is composed of two major chromosomal groups, 2
n=48 type and 2
n=46 type. The former was tentatively named as
A. speciosus group I and the latter as
A. specious group II (Table 3) .
Biochemical as well as immunological characters of various blood components of these two chromosomal groups were compared. There was no difference between the two in the electrophoretic mobilities of albumin, hemopexin-like protein, transferrin and S α
2-macroglobulin (Fig. 6) . A comparison of electrophoretic pattern of serum α-esterase revealed a slight difference in the number of bands, but it was not enough to clearly distinguish the two groups. No significance was detected in immunogenecity of serum proteins examined by immunoelectrophoresis (Fig. 8), red blood cell antigenecity (Table 3) and the temperature sensitivity of liver acid phosphatase (Fig. 9) . In
A. miyakensis, however, electrophoretic pattern of serum proteins differed obviously from that in the other species (Fig. 10) . Further, specimens from Kohzu Island (
A. n. insperatus ?) showed two kinds of albumin in the electrophoretic mobility either
A. speciosus type or
A. miyakensis type.
The results obtained in the present study suggest some revisions in the current classification system of the
A. speciosus group : 1)
A. s. speciosus is to be subdivided into two groups on the basis of their karyological features,
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