sample collection : in total , 95 crania were examined : 50 h. i. 
 inermis ( =30 , =20 ) and 45 h. i. argyropus ( =28 , =17 ) ( table 1table 1.the number and property of specimen in this studyh . i. argyropush . i. inermistotalmale28 ( seoul national univ.)30 ( ecnu : 3 , sstm : 6 and cas : 21)58female17 ( seoul national univ.)20 ( sstm : 2 , cas : 18)37total455095ecnu : east china normal university , shanghai ; sstm : shanghai science & technology 
 museum ; cas : chinese academy of sciences , beijing . ) . the specimens were from museums including east china normal university 
 ( ecnu ) , shanghai ; the shanghai science and technology museum ( sstm ) , shanghai ; and the 
 chinese academy of sciences ( cas ) , beijing . as locality information for some of the chinese 
 specimens was missing , we considered all of these specimens as one chinese population . for 
 the korean water deer , all specimens were collected by the conservation genome resource bank 
 for korean wildlife ( cgrb ) and kept in the department of anatomy and cell biology , college 
 of veterinary medicine , seoul national university . specimens were limited to adults with 
 fully erupted teeth to avoid age - related bias . ecnu : east china normal university , shanghai ; sstm : shanghai science & technology 
 museum ; cas : chinese academy of sciences , beijing . measurements and statistical analyses : following the definitions of von 
 den driesch , 36 linear measurements ( fig . a : akrokranion , b : basion , ect : ectorbitale , ent : 
 entorbitale , if : infraorbitale , l : lambda , n : nasion , p : prosthion , pm : premolare , po : 
 palatinoorale , rh : rhinion , s : synsphenion , st : staphylion , and zy : zygion . and table 2table 2.measurements of craniaabbreviationvariabletltotal lengthcblcondylobasal lengthblbasal lengthsslshort skull lengthpppremolar  prosthionbcabasicranial axisbfabasifacial axisnclneurocranium lengthvclviscerocranium lengthmflmedian frontal lengthlnlambda  nasionlrlambda  rhinionlplambda  prosthionakiakrokranion  infraorbitale of one sideglngreatest length of the nasalsslsnout lengthmplmedian palatal lengthoploral palatal lengthllplateral length of the premaxillalmprlength of the molar and premolar rowlmrlength of the molar rowlprlength of the premolar rowlo1length of the upper orbitlo2length of the lower orbitgmbgreatest mastoid breadthgbocgreatest breadth of the occipital condylesgbbgreatest breadth at the bases of the paraoccipital 
 processesgbfmgreatest breadth of the foramen magnumghfmgreatest height of the foramen magnumlfbleast frontal breadthzbzygomatic breadthlboleast breadth between the orbitsgbogreatest breadth across the orbitsgbngreatest breadth across the nasalsgbpgreatest breadth across the premaxillaebcbasion  the highest point of the superior nuchal crestnumbers correspond measurements shown in fig . 
 2 . were taken on the right side of each skull by one of the authors ( y.k.k . ) to 
 the nearest 0.01 mm with digital vernier calipers ( mitutoyo , tokyo , japan ) . a : akrokranion , b : basion , ect : ectorbitale , ent : 
 entorbitale , if : infraorbitale , l : lambda , n : nasion , p : prosthion , pm : premolare , po : 
 palatinoorale , rh : rhinion , s : synsphenion , st : staphylion , and zy : zygion . have not yet been reported in this species , we examined the 
 differences in each skull measurement between males and females of both subspecies with a 
 student s t - test using pasw statistics v18 program ( ibm , chicago , il , 
 u.s.a . ) . principal 
 component analysis ( pca ) and subsequent varimax rotation were attempted to analyze the 
 variation pattern using pasw statistics v18 program ( ibm ) . standardized cronbach s alpha value was estimated to assess the reliability of 
 the principal component analysis . the statistical certainty of assignment for individuals 
 into their reference populations was evaluated by discriminant analysis ( da ) . the overall morphological similarities between and within the two populations were 
 calculated using a euclidean distance matrix by poptools . each euclidean morphological distance value ( ed ) was 
 recalculated with the formula 1/(1+ed ) to set maximum and minimum values . using this formula , all morphological distance values were converted into the range 01 . 
 here , the pairwise similarity value approaches 1 with increasing morphological similarity 
 between the 2 populations . the hierarchical cluster diagram was drawn using measurement data 
 in past version 2.12 . in this clustering 
 analysis , the neighbor - joining ( nj ) clustering and the unweighted pair group method with 
 arithmetic mean ( upgma ) clustering methods were conducted to test hierarchical topology 
 among these specimens and were assessed by 1,000 bootstrap replicates . univariate analysis : mean values of 7 skull measurements from female 
 specimens ( bfa , lmpr , gboc , gbb , lfb , gbo and bc ) and male specimens ( gln , lmpr , lpr , gbb , 
 gbfm , lfb and bc ) were significantly larger for h. i. argyropus than 
 h. i. inermis ( table 
 3table 3.mean ( in millimeters ) and standard deviation ( s.d ) of measurementsmeasurementsmalefemaleargyropusinermisargyropusinermismeans.dmeans.dmeans.dmeans.dgeometric mean56.1555.8557.1056.12tl168.334.87169.223.96173.263.56172.544.78cbl158.245.19158.593.67163.133.31162.254.79bl147.794.99148.623.50152.873.41152.074.52ssl94.362.3494.292.4397.151.9696.373.39pp53.393.0754.241.9255.672.6555.442.35bca36.641.6236.992.1137.821.9339.913.68bfa113.313.81113.813.60117.113.32114.164.35ncl93.213.3393.783.4194.581.9993.183.74vcl81.263.5681.293.0684.793.3984.053.17mfl93.803.2394.543.2095.102.1794.383.99ln83.253.0983.323.3583.682.2583.574.09lr135.563.86133.344.76138.023.84135.933.80lp160.674.80160.734.31164.733.95164.224.77aki117.233.08117.293.22120.141.87119.444.01gln52.913.5050.933.9354.993.3753.103.39sl80.672.8281.132.6384.152.9583.482.96mpl95.614.3897.403.54100.183.3699.562.97opl72.403.4673.202.3175.382.9274.472.71llp46.723.0646.693.0049.043.1648.342.64lmpr50.172.2248.841.9649.912.4048.322.29lmr27.981.1127.901.3527.871.4627.451.47lpr23.771.5722.971.0423.821.5422.891.25lo125.441.0425.510.7926.050.8625.861.08lo225.241.2224.990.9325.261.0025.130.95gmb47.281.6247.391.9347.451.9946.931.78gboc29.212.4128.211.2129.280.8728.131.15gbb41.871.2740.811.5742.251.6739.891.60gbfm14.390.8313.860.8314.060.9514.081.18ghfm14.870.8214.640.9414.591.3014.971.16lfb71.972.6670.122.6673.322.1669.223.06zb39.251.9138.222.2140.603.0239.392.01lbo71.202.6271.112.6471.942.4571.533.13gbo16.291.7416.242.3516.761.5415.291.52gbn29.592.4531.282.1226.802.5625.931.86gbp51.432.1851.691.7252.702.0151.442.08bc41.721.5440.921.4842.071.3040.821.59bold : significant difference between korea and china . ) . in contrast , one measurement from females ( bca ) and from males ( gbn ) was 
 significantly larger for h. i. inermis than h. i. 
 argyropus . in addition , most average values for all other measurements , which 
 were not significantly different between subspecies , were larger in h. i. 
 argyropus than h. i. inermis in females . pca : in the pca of cranium measurements , the first ( f1 ) and second ( f2 ) 
 components explained 37.90% and 10.53% of the total variation in males ( table 5table 5.principal components of males which account for more than 1 of eigenvalue from 
 pcavariablepc1pc2pc3pc4pc5pc6pc7pc8tl0.7690.5350.1740.0170.1700.0330.1700.012cbl0.8410.3770.1910.0940.0730.0350.0050.114bl0.8440.4550.1680.0650.0630.0420.0460.041ssl0.5600.6730.2090.2230.0270.0020.0580.017pp0.8800.1350.0730.3000.0970.0890.1390.066bca0.1130.6530.0050.3400.3110.2020.2840.147bfa0.8990.2020.1550.1150.0810.0130.2030.070ncl0.0520.6410.0290.1230.0530.3980.1560.284vcl0.8380.0950.0340.0220.4450.0350.0590.056mfl0.1990.8770.1420.0340.1730.0930.2220.028ln0.1970.8460.1740.1020.1180.0260.2560.048lr0.4590.4140.1700.0850.5920.0200.2530.231lp0.7590.4990.1590.0770.2230.0300.2060.077aki0.5180.6830.2740.0380.1720.0420.2050.130gln0.4100.2230.0290.0140.7670.0220.1020.218sl0.8630.1910.1210.0210.1990.1220.0360.002mpl0.9090.001 - 0.0680.0270.0410.0250.1000.219opl0.8500.0890.1190.0400.0470.1260.0910.247llp0.5340.0590.1340.0080.4050.0890.0170.090lmpr0.0200.0400.0370.9530.0530.0320.0830.111lmr0.0670.1490.1700.8230.0550.2460.0610.014lpr0.2010.0680.1970.8470.0210.2200.1310.052lo10.1330.3190.2300.1300.1570.0970.7350.241lo20.3280.1710.1960.0990.0190.0890.7580.011gmb0.1980.5450.5100.0970.1290.1060.0350.036gboc0.3950.1110.1930.0230.0200.5760.3110.223gbb0.1790.0430.6220.1130.0930.4600.1260.091gbfm0.0070.0890.0860.0610.0020.8380.2050.084ghfm0.2040.0680.1840.0330.1120.4470.0780.481lfb0.1170.2080.8190.0320.1890.1040.2460.065zb0.0180.2270.5530.1370.1800.3040.0640.141lbo0.2620.0930.6780.0390.2050.1670.3760.264gbo0.0890.0050.3560.0280.6770.0310.0350.210gbn0.0430.0590.2260.2610.0360.0140.1550.704gbp0.2750.1710.6460.1590.0520.0570.3500.392bc0.3380.3300.4570.0810.0270.4270.0950.220eigenvalue13.6453.7902.9702.5312.2561.4791.2291.024proportion37.90310.5278.2517.0306.2684.1093.4152.844cumulative37.90348.43056.68163.71169.97974.08877.50480.347bold : absolute > 0.5 . ) , and 32.86% and 14.43% of the variation in females ( table 6table 6.principal components of females which account for more than 1 of eigenvalue from 
 pcavariablepc1pc2pc3pc4pc5pc6pc7pc8tl0.8650.4020.1130.0080.0980.0460.1190.114cbl0.8420.3390.0740.1120.1820.1810.0640.125bl0.8450.3170.0570.1610.1440.1920.0690.196ssl0.4970.4680.0630.1860.2330.3360.1870.460pp0.8080.0110.1730.4150.0100.084 - 0.1290.178bca0.1680.0660.1960.1740.1660.1080.8540.001bfa0.6270.2720.0710.0080.2690.0810.5720.197ncl0.2170.7780.0680.2540.3030.2050.0650.060vcl0.8890.3250.0210.0360.0910.0150.0460.168mfl0.2350.8610.1400.2540.0490.0910.0760.009ln0.3330.8340.1040.2680.0980.0950.0510.108lr0.7120.2890.2570.2610.1520.0970.0110.330lp0.9040.3320.0790.0630.0280.0590.1160.019aki0.5860.6130.1810.1310.1240.0430.1840.240gln0.4420.5110.1450.1060.2280.0130.0650.524sl0.9030.0360.1900.0890.0920.1220.0240.144mpl0.8230.0780.1570.0700.1940.0920.0860.102opl0.8230.0840.1290.2380.0570.0470.2090.231llp0.6350.0400.2330.0690.0950.1960.1700.114lmpr0.1250.1780.0340.9390.1080.0360.1360.050lmr0.2870.1190.1290.8680.1020.0140.0690.208lpr0.1040.0790.0940.8840.1090.0710.1040.119lo10.0800.7240.2920.1910.1400.0550.2040.150lo20.4010.0640.3570.0900.0630.1470.1460.501gmb0.1790.0700.7860.1260.0170.0150.1120.179gboc0.0560.0260.0140.1360.7950.2370.2230.036gbb0.1220.0330.5110.0110.6340.0060.0190.050gbfm0.1860.0080.0890.2130.2860.7890.0340.226ghfm0.1450.0100.1150.2050.0810.7900.0730.177lfb0.1870.2430.8100.0190.0770.0540.1080.001zb0.0050.3780.3230.0530.3540.5380.1040.142lbo0.1340.1710.7860.2720.0180.0950.2270.206gbo0.1600.1570.7300.0010.3410.1430.0670.075gbn0.0250.5440.4990.1440.2210.3120.0340.058gbp0.0330.2030.8610.0240.0700.1220.0410.143bc0.1900.1760.3270.2820.6910.0330.0570.134eigenvalue11.8305.1953.8923.1411.8271.6741.1991.085proportion32.86214.43010.8118.7245.0764.6513.3313.013cumulative32.86247.29358.10466.82871.90476.55579.88682.898bold : absolute > 0.5 . ) . the reliability of this analysis as tested by standardized cronbach s alpha 
 was 0.94 in males and 0.92 in females . the first 8 components which account for more than 1 eigenvalue 
 explained 80.35% of total variance for males ( table 
 5 ) . for the pc1 of males , values of thirteen components ( tl , cbl , bl , ssl , pp , bfa , 
 vcl , lp , aki , sl , mpl , opl and llp ) were significant . for females , the first 8 components 
 which account for more than 1 eigenvalue explained 82.90% of total variance for females 
 ( table 6 ) . for the pc1 of females , values of 
 thirteen components ( tl , cbl , bl , pp , bfa , vcl , lr , lp , aki , sl , mpl , opl and llp ) were 
 significant . in the scatter plots , 3.two-dimensional scatter plots of the first and second principal component scores of 
 males ( up ) and females ( down ) . factor loading values of males and females were not significantly different 
 ( p>0.05 ) . two - dimensional scatter plots of the first and second principal component scores of 
 males ( up ) and females ( down ) . da : the result of da could not discriminate populations significantly for 
 males and females ( p=0.359 for males and p=0.487 for 
 females ) . from da , 70.69% of males and 75.69% of females 4.frequency distribution of discriminant analysis by males ( up ) and females ( down ) . p - value=0.359 for males and 0.487 for females . is a bar plot of the da between the two populations . frequency distribution of discriminant analysis by males ( up ) and females ( down ) . morphological distance and cluster analysis : the within - population and 
 inter - population morphological similarities computed by the euclidean method were estimated 
 for both sexes ( table 4table 4.pairwise morphological distance matrixmaleargyropusinermisfemaleargyropusinermisargyropus0.972argyropus0.973inermis0.9710.972inermis0.9700.971 ) . for males , the 
 intra - population morphological similarity was 0.972 for both populations , and the 
 inter - population distance was 0.971 . for females , the intra - population similarity was 0.973 
 for the korean population and 0.971 for the chinese population . ( c : chinese 
 population ; k : korean population ; m : male ; f : female ) . ( c : chinese 
 population ; k : korean population ; m : male ; f : female ) . show the results of cluster analysis using the upgma and nj methods , respectively , as 
 well as the cladogram topology . both methods showed that specimens from each population had 
 mixed topologies in two cladograms ; the morphological distance ( = similarity , y - axis ) was 
 < 1% in the upgma cladogram . ( c : chinese 
 population ; k : korean population ; m : male ; f : female ) . ( c : chinese 
 population ; k : korean population ; m : male ; f : female ) . morphological differences between h. i. inermis and h. i. argyropus : the 
 present study investigated the 2 subspecies of water deer ( h. inermis ) 
 distributed in korea and china . the major goal of this research was to morphologically test 
 the conventional subspecific classification of this species . the results of a student s 
 t - test and pca suggested that these 2 subspecies are not 
 well - differentiated , meaning that individuals of the 2 populations share common 
 morphological traits . da results also indicated that some individuals share characteristics 
 of both populations , suggesting that not all individuals can be assigned to their original 
 population based on morphometrics . the results of cluster analysis using 2 different 
 algorithms , nj and upgma , showed that specimens of the two populations had highly mixed 
 topologies in the cladograms . previous research has confirmed that the 2 subspecies have a close genetic distance , with 
 an average genetic distance of 2.1% in the control region and 1.3% in cytochrome 
 b . the topology of a 
 phylogenetic nj tree from the control region and cytochrome b showed that 
 h. i. inermis and h. i. argyropus blended within a major 
 clade . in the present study , it was found that the morphological distance between the 
 populations was also very close . the inter - population similarity was almost the same as the 
 intra - population similarity . these facts suggest that the 2 populations can not be clearly 
 distinguished genetically nor morphologically . bergmann s rule posits that body size is negatively correlated with temperature among 
 closely related species in mammals and birds [ 4 , 15 ] . this pattern has been pointed out to be obvious , 
 especially within species [ 19 , 20 ] and has been regarded as one of the major factors producing 
 within - species geographic variation [ 10 , 25 ] . however , our results show that water deer do not 
 follow bergmann s rule . tl , which represents skull size , was not significantly different 
 between h. i. inermis and h. i. argyropus ( table 3 ) . the zhoushan islands , the habitat of the 
 chinese water deer in central china ( fig . 1a ) , are 
 located around 30n latitude , and korean water deer are distributed around 3538n latitude . similar to the present results , others have demonstrated that this rule is not always 
 applicable [ 3 , 7 , 22 , 24 , 27 , 29 ] . although the reason for the lack of clear morphocline in water deer is yet 
 unclear , the establishment of current distribution of this species was perhaps a relatively 
 recent event , producing the observed genetic and morphological homogeneity . necessity to reconsider the subspecies classification of water deer : 
 subspecies of water deer were initially designated by swinhoe   and heude . although the 
 concept of subspecies has varied , it is generally defined as members of a polytypic species , 
 not simply as a  slightly different  local population . results of pca indicate that the 2 populations show more than 75% of overlap 
 and reject the subspecies classification under the phylogenetic analysis studying the mtdna proposed that the subspecific 
 classification may not be valid and indicated the need for examination of this issue from a 
 morphological perspective . our results 
 demonstrate that there is no clear difference in craniodental morphology between the 2 
 populations , lending further support to the reconsideration of the subspecific 
 classification of water deer . the differences between the chinese and korean populations are 
 thus not exceptional , other than their pelage color . however , the pelage color variation has not been studied quantitatively and 
 remains to be evaluated . although the chinese water deer was originally distributed widely throughout china , these 
 animals have gradually become rarer , and their distribution has been fragmented over the 
 past century due to poaching for traditional medicine and habitat destruction by 
 industrialization [ 12 , 30 , 32 , 33 ] . today , the chinese water deer is classified as a vulnerable species 
 by the international union for conservation of nature ( iucn ) . in contrast to the situation in china , korean water deer are 
 distributed throughout the korean peninsula , where its numbers are both stable and abundant 
 . if the population of chinese water deer 
 continues to decrease , plans for restoration will become more urgent . given the homogeneity 
 of chinese and korean water deer demonstrated by molecular evidence   and morphological evidence ( this study ) , the introduction of korean 
 water deer into the chinese population might be the most logical , and ultimately successful , 
 restoration strategy .
the water deer ( hydropotes inermis ) has conventionally been classified 
 into two subspecies according to geographic distribution and pelage color pattern : 
 h. i. inermis from china and h. i. argyropus from 
 korea . 
 however , the results of a recent molecular study have called this into question . 
 to 
 further reappraise this classification , we examined morphological variation in 
 craniodental measurements of these 2 subspecies . 
 results of univariate and multivariate 
 analyses demonstrated that these 2 subspecies are not well - differentiated , suggesting that 
 individuals of the 2 populations share common morphological traits . despite the 
 distribution of the subspecies at different latitudes , 
 no clear morphocline was detected , 
 suggesting that bergmann s rule does not apply in this case . 
 discriminant analysis 
 indicated that the characteristics of individuals are shared by both populations , 
 suggesting that not all individuals can be assigned to their original population . 
 results 
 of principal component analysis showed that the two populations shared more than 75% of 
 individuals , congruent with the 
 75% rule  of subspecies classification . in both the 
 neighbor - joining and unweighted pair group methods with arithmetic mean 
 cluster analyses , 
 specimens of h. i. argyropus and h. i. inermis were 
 highly mixed within the cladograms . 
 these results suggest that the overall morphological 
 variation in the 2 subspecies overlaps considerably and that there is no coherent 
 craniofacial difference between the 2 groups . 
 the present findings combined with prior 
 observations from molecular biogeography point out that the taxonomic division of water 
 deer into 2 subspecies should be revisited .