Craniometric and molecular genetic characteristics of the Korean Water Deer, Hydropotes inermis argyropus

Abstract

The water deer, Hydropotes inermis, is the only species of genus Hydropotes and 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. Contrasted with the Chinese water deer, the Korean subspecies has been rarely studied. In this dissertation, some morphological and genetic characteristics of the Korean water deer populations were investigated. This volume consists of two parts (Chapter I for morphological and Chapter II for genetic studies). In Chapter I, three different topics were executed. First, the skull growth of the Korean water deer was analyzed using craniometric method. Second, the sexual dimorphism of skull of the Korean water deer was evaluated using cranio-mandibular analysis. Third, the morphological differences of crania between two subspecies of water deer (H. i. inermis and H. i. argyropus) were determined, based on the cranial measurements. In Chapter II, two different topics in one chapter were studied. First, mitochondrial cytochrome b gene diversity and phylogeny of the Korean water deer were examined. Second, population structure of the Korean water deer was analyzed. For the first topic, craniomandibular traits of the water deer from the Korean Peninsula were examined to assess size change in growth between age groups and sexes. Univariate and multivariate analyses were conducted based on 34 cranial and 11 mandibular measurements from both sexes. Statistical comparisons of skull measurements revealed a significantly different growth pattern between the sexes. For the male, the size change of the cranium and mandible was straight through age groups, constantly. On the other hand, the size of the cranium and mandible of the female was changed relatively steeper than that of the male in age groups 2 to 3, and the growth curves from age group 3 to 4 were more gradual than age groups 2 to 3. Principal component analysis showed that these 2 sexes have a similar trend. In the allometry analysis, there were differences in growth in 5 traits in both sexes. In conclusion, my study suggests that the male and the female Korean water deer had a similar trend for their growth, although there was a small difference of skull growth for age groups. For the second topic, Sexual dimorphism in the craniomandibular traits in the Korean water deer was examined for the first time. Multivariate analyses using only cranial traits showed a clear separation between sexes. However, the separation was not obvious in the discriminant analysis using only mandibular traits. The most clearly dimorphic trait was in the incisive bone breadth, which was about 12% larger in males. The incisive bone breadth reflects the characteristically large canines in male. In contrast to this, most of the cranial measurements, except for the incisive breadth, were larger in female, indicating a larger overall skull size. Given that males are generally larger than females, this sexually dimorphic pattern is unique among mammals. I propose that factors, for example, a unique parental care, have influenced the larger skull size in the females of this species. The water deer has conventionally been classified into two subspecies according to geographic distribution and pelage color pattern: Chinese water deer from China, and Korean water deer from Korea. However, the results of a recent molecular study have called this into question. To further reappraise this classification, I examined morphological variation in craniodental measurements of these two subspecies. Results of Students t-test analysis and multivariate analyses demonstrated that these two subspecies are not well-differentiated, suggesting that individuals of the two populations share common morphological traits. Despite the distribution of the subspecies at different latitudes, no clear morphocline was detected suggesting that Bergmanns rule does not apply in this case. Discriminant analysis indicated that the characteristics of some 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 two subspecies overlaps considerably and that there is no coherent craniodental difference between the two groups. The present findings combined with prior observations from molecular biogeography point out that the taxonomic division of water deer into two subspecies should be revisited. For the fourth topic, we analyzed 1,140 base pair of mtDNA cytochrome b gene and 12 microsatellite markers of the Korean water deer, respectively. Twenty-one haplotypes were detected in 51 samples from three regional populations in the Korea, and the overall genetic diversity was relatively low compared to the Chinese water deer, sister taxa of the Korean water deer. Although phylogenetic analysis revealed that there are two distinct clades, the regional division was not detected. Microsatellite variability was not significant among three populations (mean FST = 0.008) and it means that there is no population structure. These results suggest that the Korean water deer populations show a single population although there were two distinct clades. As basic, essential and useful information for animal research, this data will be helpful for conservation. These results from the four topics in Chapter I and II show that these fundamental and integrative studies of the Korean water deer will be useful to understand the morphological and genetic characteristics, and furthermore to perform its conservation and management strategy in Korea and China.