FULL PAPER Anatomy Geographical Variation of the Skull of the Lesser Mouse Deer Hideki ENDO1), Katsuhiro FUKUTA2), Junpei KIMURA3), Motoki SASAKI4) and Brian J. STAFFORD5,6) 1)Department of Zoology, National Science Museum, Tokyo, 3–23–1 Hyakunin-cho, Shinjuku-ku, Tokyo 169–0073, 2)Laboratory of Animal Morphology and Function, Graduate School of Bioagricutural Sciences, Nagoya University, Nagoya, Aichi 464–8601, 3)Department of Veterinary Anatomy, College of Bioresource Sciences, Nihon University, Fujisawa, Kanagawa 252–8610, 4)Department of Veterinary Anatomy, Obihiro University of Agriculture and Veterinary Medicine, Obihiro, Hokkaido 080–8555, Japan, 5)Mammal Division, National Museum of Natural History, Smithsonian Institution, Washington DC. and 6)Department of Anatomy, Howard University College of Medicine, Washington DC, U.S.A. (Received 21 January 2004/Accepted 1 June 2004) ABSTRACT. We examined the geographical variation of the skull size and shape of the lesser mouse deer (Tragulus javanicus) from Laos, Thailand, Peninsular Malaysia, Sumatra, Java, Borneo, Langkawi and some Islands of Tenasserim in Myanmar. Although the influence of the climatic condition on skull size was not confirmed in the mainland populations, the skull became rostro-caudally longer in the populations of Tenasserim and Sumatra because of island isolation effect. The skull size was classified into the following three clusters of localities from the matrix of Q-mode correlation coefficients: 1) Langkawi and Tenasserim, 2) Laos and Thailand, 3) Sumatra and Borneo. The skulls in the population of Java belong to the cluster of Langkawi and Tenasserim in male, however were morphologically similar to those in the cluster of Borneo and Sumatra. The canonical discriminant analysis pointed out that the Laos and Tenasserim populations were separated from the other ones and that the populations of Sumatra, Java and Borneo were intermingled each other. KEY WORDS: geographical variation, lesser mouse deer, osteometry, skull, Tragulus javanicus. J. Vet. Med. Sci. 66(10): 1229–1235, 2004 The lesser mouse deer (Tragulus javanicus) is largely dis- ness of the skull suture was not examined in this study. tributed in the Indomalayan region including Thailand, Skull measurement was carried out utilizing vernier calli- Cambodia, Laos, Vietnam, Myanmar, Peninsular Malaysia, pers until the nearest 0.05 mm. The measurements, which Sumatra, Java, Borneo and some islands [14]. Some races were based on Driesch [5] and Duerst [6], are defined in have been described within Tragulus javanicus and the tax- Table 2. Since the incisive bone had been easily broken and onomic discussion was confusing about this species [1, 2, lost in this species, we used the most cranial point of the 12, 13, 15–17, 21]. Although the conflicting studies have maxilla instead of the Prosthion of the incisive bone in the dealt with skin color, external measurements and skull mor- four length measurements (PL2, BL2, SL2 and MPL2) phology in a few individuals at the subspecies level, the sta- (Tables 1 and 2). tistical analysis of the skeleton [23] and the taxonomical The statistical analysis was undertaken in each sex. To reviews [3, 24] have pointed out that only two species of tra- clarify the geographical tendency in size among the popula- gulids, Tragulus javanicus and Tragulus napu, should be tions of Laos, Tenasserim, Peninsular Malaysia, Sumatra, recognized in the Indomalayan region at the species level. Java and Borneo including many specimens, statistical dif- We reported the growth pattern of the skull in the lesser ference among mean values of each measurement was ana- mouse deer [20], however the geographical variation has lyzed by Student’s t-test. Using the measurement data the remained unclear in the skull morphology in Tragulus jav- clustering analysis was carried out to evaluate the osteomet- anicus. rical similarities between populations. Since we also applied the specimens without incisive bone for clustering MATERIALS AND METHODS analysis, the 21 measurements except for PL1, BL1, SL1, and MPL1 were used. The clustering was performed by We examined totally 221 skulls of the lesser mouse deer UPGMA method for the distance matrix converted from the (Tragulus javanicus). These specimens are housed in the matrix of the Q-mode correlation coefficients to avoid loss Smithsonian Institution (Washington DC, U.S.A.), Ameri- of information [19]. The distance matrix and the dendro- can Museum of Natural History (New York, U.S.A.), gram between localities were obtained by using the software Nationaal Natuurhistorische Museum (Leiden, The Nether- of Statistica (StatSoft, Inc, Tokyo, Japan). The canonical lands), and National Science Museum, Tokyo (Tokyo, discriminant analysis was also undertaken using the 7 local- Japan) (Appendices 1 and 2). Sex determination was depen- ity groups except for Thailand population, since the male dent on the description of biological data and the canine size population from Thailand including only one specimen of the specimens. We selected specimens that possessed the could be applied to the analysis. The first two canonical dis- fully erupted lower third molar and considered them adult. criminant functions were calculated and plotted by using the The composition of the origin and the sex is shown in Table software of Statistica. 1. Each locality is indicated in the map (Fig. 1). The close- 1230 H. ENDO ET AL. Appendix 1. Specimen No. used in this study (male) Symbol L Vientiane National Science Museum, Tokyo 31072 31085 31086 31087 31088 31092 31099 31109 31110 31114 31125 31127 T Surathani Smithsonian Institution 255718 E Tenasserim (James Id., Kisseraing Id., Mergui Id., St. Matthews Id., and St. Luke's Id.) Smithsonian Institution 104419 104423 104424 104426 104427 104428 124029 124038 124145 124178 M Peninsular Malaysia Smithsonian Institution 115371 115372 115376 283560 489437 489440 489442 489445 SSumatra Smithsonian Institution 114328 114329 114331 114339 114340 114419 114420 114426 114427 143318 143321 143488 143489 143497 143500 143501 143502 143503 143504 143514 143515 143516 143517 143518 143523 143524 144140 144145 144146 144150 144153 144155 144157 144313 144356 144357 144367 144368 144370 145325 145326 American Mueum of Natural History 106551 106553 Nationaal Natuurhisorische Museum, Leiden 4600 11811 33768 JJava Smithsonian Institution 194246 American Mueum of Natural History 102090 Nationaal Natuurhisorische Museum, Leiden* 172 4936 33767 33778 194246 T-102 T-105 T-106 BBorneo Smithsonian Institution 19191 145354 145355 145357 145358 145359 145360 145361 153740 153742 153744 153746 153747 153748 153752 153754 154350 197687 197688 197689 American Mueum of Natural History 103696 103696 106070 106297 107110 107111 Nationaal Natuurhisorische Museum, Leiden* T-18 T-20 T-27 T-28 A Langkawi Id. Smithsonian Institution 104404 104405 104406 104407 * The numbers with the symbol T are temporary for this study. RESULTS pared between the M mainland population and the E, S, and B island ones. The size-related measurements such as PL1, Mean values and standard deviations in 25 measurements PL2, BL1 and BL2 were significantly larger in E and S pop- are shown in Table 3. The data on the significant differ- ulations and females of J population than in M population ences between localities are arranged in Table 4. (Tables 3 and 4). In contrast, the skull size of Borneo popu- We compared the L mainland population with M to con- lation was not significantly different from that of Peninsular firm the influence of the climatic conditions on the skull size Malaysia population. OZW and AZW were not signifi- by the following reasons: the distribution of the two popula- cantly different between the M population and the island tions is obviously separated into the north and south districts populations unlike the measurements on the entire length. of the Indochinese and Malayan Peninsulae; the conditions As for the length measurements of the splanchnocranium of the temperature and precipitation in Vientiane District are the mean values were significantly smaller in SL1, SL2, different from those in Peninsular Malaysia. The mean val- MPL1 and MPL2 in M population than those in E and S ues of PL1, PL2, BL1 and BL2 in both sexes were larger in populations. However, the other comparisons between the the Laos population than those in the Peninsular Malaysia M population and the island populations did not obviously one, though the significant difference was not found in some show statistical differences. The values of LBO and LBS cases (Tables 3 and 4). were significantly larger in S population than in M one, The island-isolation effects on skull size could be com- which indicated the development in the width of the SKULL VARIATION OF LESSER MOUSE DEER 1231 Appendix 2.Specimen No. used in this study (female) Symbol L Vientiane National Science Museum, Tokyo 31076 31077 31078 31081 31103 31104 31105 31106 31107 31108 31122 31124 T East Thailand Smithsonian Institution 236613 253408 258875 E Tenasserim (James Id., Kisseraing Id., Mergui Id., St. Matthews Id., and St. Luke’s Id.) Smithsonian Institution 104431 104420 124025 124026 124027 124030 124035 124037 124040 124085 124086 124179 124245 M Peninsular Malaysia Smithsonian Institution 115368 115369 115373 489439 489444 SSumatra Smithsonian Institution 114330 114332 114333 114338 114421 114422 114424 114425 121697 121698 121838 123108 143319 143493 143494 143495 143496 143498 143499 143506 143507 143508 143509 143511 143512