A New Species of Ryukyu Spiny Rat, Tokudaia (Muridae: Rodentia), from Tokunoshima Island, Kagoshima Prefecture, Japan
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Mammal Study 31: 47–57 (2006) © the Mammalogical Society of Japan A new species of Ryukyu spiny rat, Tokudaia (Muridae: Rodentia), from Tokunoshima Island, Kagoshima Prefecture, Japan Hideki Endo1,* and Kimiyuki Tsuchiya2,** 1 Section of Morphology, Primate Research Institute, Kyoto University, Inuyama, Aichi 484-8506, Japan 2 Laboratory of Wild Animals, Department of Animal Sciences, Faculty of Agriculture, Tokyo University of Agriculture, Atsugi, Kanagawa 243-0034, Japan Abstract. A new species of Ryukyu spiny rat, Tokudaia tokunoshimensis was described in the specimens originating from Tokunoshima Island in the southernmost region of Japan. The populations of Tokudaia are separately distributed only in Amami-Oshima, Tokunoshima, and Okinawa-jima Islands. We have described the osteological and external morphological characteristics and clarified the osteometrical distinctions among the three populations using the skull and skin collections. All external dimensions of head and body length, tail length, hindfoot length and ear length were larger in the Tokunoshima population than in the other two in mean value. The raw osteometrical data separated the Tokunoshima Island population from the other two in all measurements except for the length of molar row in the Okinawa-jima Island population. The principal component analysis also demonstrated that the skulls from the Tokunoshima Island population were morphologically distinct from those of the other populations. Here, from these findings, we point out that the Tokunoshima population of Tokudaia should be regarded as an independent species from the two other populations. Key words: osteology, Ryukyu spiny rat, Tokudaia muenninki, Tokudaia osimensis, Tokunoshima. The Ryukyu spiny rats (genus Tokudaia) are distributed mal DNA (Tsuchiya et al. 1989), the mitochondrial DNA only in the three Islands of Amami-Oshima, Tokuno- sequence data also suggested that the population in shima and Okinawa-jima in the Ryukyu Islands of Japan. Tokunoshima Island were taxonomically separated from The first taxonomical record of the Ryukyu spiny rat was the population in Amami-Oshima Island (Suzuki et al. from the population in Amami-Oshima (Abe 1933), and 1999). All the other genetic data including blood serum the new genus Tokudaia was described for the popula- polymorphisms have consistently indicated the differen- tions (Kuroda 1943). Since the body size is larger in the tiations at a species level of the genus Tokudaia among Okinawa-jima Island population than in the Amami- the three populations. Oshima Island one, the population of Ryukyu spiny rat The detailed osteometrical comparisons (Kaneko from Okinawa-jima Island had been considered as a sub- 2001) demonstrated that the skulls of the Okinawa-jima species of Ryukyu spiny rat from Amami-Oshima Island population had a longer row of upper teeth from the inci- (Johnson 1964), and after that it had been generally sor to the third molar and possessed a wider first upper named as T. osimensis muenninki as shown in the species molar than those of the Amami-Oshima population, lists of the Asian mammals (Ellerman and Morrison- while the palatine foramen was situated more posteriorly Scott 1951; Corbet and Hill 1992). in the skulls of the Okinawa-jima population than those The variations of karyotype were obviously revealed of the Amami-Oshima population. These skull charac- among the three island populations of Tokudaia (Honda teristics supported the theory that the two populations et al. 1977, 1978; Tsuchiya 1979, 1981; Tsuchiya et al. should belong to the valid species T. muenninki and T. 1989). In addition to the restriction fragments length osimensis, respectively, unlike the original work on the polymorphisms of the mitochondrial DNA and riboso- Okinawa-jima population (Johnson 1964). However, no *To whom correspondence should be addressed. E-mail: [email protected] **Present address: Ooyo-Seibutsu Co. Ltd., 4-12-3 Minami- Aoyama, Minato-ku, Tokyo 107-0062, Japan 48 Mammal Study 31 (2006) morphological comparison using the Tokudaia speci- Table 1. Locality and sex composition of the skull specimens. mens from Tokunoshima Island has been carried out. Origin of Specimens Symbols Male Female Tokunoshima T 1 2 Materials and methods Amami-Oshima A 11 5 Okinawa-jima O 7 3 We examined 29 skulls of the Ryukyu spiny rats 19 10 (genus Tokudaia) that had been stored in the Department of Zoology, National Science Museum, Tokyo (Tokyo, Japan), and the Mammal Division, the National Museum Table 2. List of measurements and their abbreviations. of Natural History in the Smithsonian Institution (Wash- Cranium ington DC, U.S.A.) (Appendix 1). Sex determination Profile length PL was dependent on the biological data for each speci- Maximum length ML men. Only specimens of adults with fully erupted molars Basal length BL were examined. The composition of origin and sex, and Short lateral facial length SL locality symbols are shown in Table 1. The skulls were Length from Prosthion to Bregma LPB Oral zygomatic breadth OZB measured with vernier calipers to the nearest 0.05 mm Zygomatic breadth ZB based on the examples of lagomorphs, artiodactyls and Maximum width of the nasal bone MWN carnivores in the textbook by Driesch (1976) (Table 2, Least breadth between the orbits LBO Fig. 1). The external measurements from the original Greatest neurocranium breadth GNB data of the specimens are also arranged in Table 2. The Greatest breadth of the occiputal condyles GBO head and body length and tail length were measured to Median palatal length MPL the nearest 0.5 mm, the hindfoot and ear lengths, to the Dental length DL nearest 1 mm. In the skull measurements the statistical Length of molar row LMR1 differences in mean values among the three populations Greatest palatal breadth GPB were examined by Student’s t-test. The proportion Length from Basion to Staphylion LBS indices were the quotients of each measurement value Length from Basion to the most rostral point of LBR zygomatic arch divided by the geometric mean of all measurement Length from Basion to the most medial point of orbit LBM values. The significant differences in proportion indices Length from Basion to Bregma LBB were examined among localities by non-parametric U- Height from Akrokranion to Basion HAB test using software Statistica (Statsoft Inc., Tokyo, Japan). Mandible The principal component analysis was also carried out Length from the condyle LC with all skull measurement data to clarify the variations Length from the angular process LA among the three geographical localities. The 16 skin Length of molar row LMR2 specimens were examined to confirm the external char- Aboral height of the vertical ramus AHR acteristics of the Tokunoshima population (Appendix 1). External measurements Head and body length HBL Tail length TL Results Hindfoot length HFL Ear length EL Taxonomic description: The measurement items of the skull were based on Driesch (1976). Tokudaia tokunoshimensis sp. nov. [Japanese name: Tokunoshima Toge-nezumi, new] M33903, adult female. These were collected in the same locality, on 17 December 1988 and 2 March 1987, Holotype: NSMT-M33901, adult female, skin and respectively, also by Kimiyuki Tsuchiya. Both are skull collected in a forest of Mikyo Area of Amagi-cho stored in the National Science Museum, Tokyo. Town in Tokunoshima Island on 14 May 1987 by Type locality: Mikyo Area, Amagi-cho Town, Tokuno- Kimiyuki Tsuchiya. The holotype is preserved in the shima Island, Kagoshima Prefecture, Japan. National Science Museum, Tokyo. Diagnosis: A middle-sized rat which is dark-brown Paratype: NSMT-M33902, adult male and NSMT- above, light gray and buff beneath. The ventral side of Endo and Tsuchiya, New species of spiny rat from Tokunoshima 49 Fig. 1. Measurements used in this study. Abbreviations are also explained in Table 2. Table 3. Skull and external dimensions (mm) in the holotype and paratype specimens. PL ML CBL SL LPB OZB ZB MWN LBO GNB GBO MPL DL LMR1 NSMT-M33901 39.60 39.45 35.40 17.25 29.45 17.75 18.40 4.55 8.05 15.45 9.25 21.25 20.40 6.15 NSMT-M33902 39.20 39.25 35.95 17.10 29.55 18.25 18.80 4.70 8.05 15.85 9.25 20.90 19.90 5.95 NSMT-M33903 38.60 38.45 35.30 17.00 28.65 18.60 18.45 4.10 7.90 15.80 9.55 20.65 19.60 6.05 Position of GPB LBS LBR LBM LBB HAB LC LA LMR2 AHR HBL TL HFL EL palatine foramen* Left Right 7.60 14.45 25.45 22.50 14.90 9.50 21.85 19.85 6.50 6.85 141.0 – 38 35 m p 7.95 14.80 26.75 22.00 15.05 9.60 21.75 20.15 6.00 6.95 170.0 – 37 34 m p 7.80 14.65 26.45 22.90 15.50 9.55 21.65 19.95 6.20 6.85 153.5 117.5 38 33 m p *Position of the palatine foramen in comparison to the postrior end line of the anterostyle of the second molar: p, postrior; m, middle position. the head and throat regions is also grayish. The tail is not is not particularly elongated. The positions of the so long, blackish on the upper and whitish on the lower palatine foramen of the skulls are arranged in Table 3. side. Its tip seems black also on the ventral side. The The auditory bulla is rounded but flat dorso-ventrally. spine is dark-brown and black, but its base is light gray. The coronoid process is not dorsally extended in the The spine is hard, and reaches 15–25 mm in length, and mandible. The photographs of the specimens are shown it cannot be seen around the mouth, ear, and extremities.