Contributions to Zoology, 79 (3) 85-92 (2010) On the discovery and origin of a Javan population of the Indochinese colubrid snake Dendrelaphis subocularis (Boulenger, 1888): a multivariate study Johan van Rooijen1, 2, 4, Gernot Vogel3 1 Netherlands Centre for Biodiversity Naturalis, section Zoological Museum Amsterdam, Mauritskade 61, 1092 AD Amsterdam, The Netherlands 2 Tulpentuin 313, 2272 EH Voorburg, The Netherlands 3 Society for Southeast Asian Herpetology, Im Sand 3, D-69115 Heidelberg, Germany 4 E-mail: [email protected] Key words: Indochina, Java, sweepstake dispersal, taxonomy, vicariance Abstract most locality record corresponding with the Isthmus of Kra (Boulenger, 1894; Wall, 1921; Smith, 1930, 1943; The colubrid snake Dendrelaphis subocularis is distributed Taylor, 1965; Vogel, 1990; Cox et al., 1998; Zug et al., throughout Indochina, the southern limit of its range corre- 1998; Grismer et al., 2007). The Isthmus of Kra repre- sponding with the Isthmus of Kra, an important biogeographic barrier that separates the Indochinese biota from the Sundaic sents an important phytogeographical and zoogeo- biota. This study presents five museum specimens that represent graphical transition zone between the Indochinese and a hitherto unknown population that inhabits the Sundaic island Sundaic regions (Smith, 1943; Hughes et al., 2003; Java. Thus, the distribution of Dendrelaphis subocularis is dis- Pauwels et al., 2003; Woodruff, 2003). The position of junct, with the Javan population being isolated by 2000 kilome- this transition zone on the Thai-Malay Peninsula is tres from the nearest mainland population. Principal Compo- nents Analysis was applied to morphological data taken from the probably associated with a change from wet seasonal five Javan specimens as well as from 26 museum specimens of evergreen dipterocarp rain forest to mixed moist de- Indochinese origin. Regression analysis of the spatial pattern of ciduous forest. However, the origin of the different the resulting scores indicated that: 1) the Javan population exhib- biotas of Sundaland and Indochina may lie in pro- its negligible morphological differentiation, and 2) a phenetic longed periods of isolation due to marine transgres- cline exists from which the Javan population does not apprecia- bly deviate in spite of its isolated status. These findings suggest sions during the Miocene and the Pliocene (Hughes et a vicariant origin of the Javan population entailing climatic al., 2003; Woodruff, 2003). The zoogeographic impor- changes and formation of land bridges during Pleistocene gla- tance of the Isthmus of Kra is applicable to the genus ciations. The Javan and Indochinese populations represent inde- Dendrelaphis. The Sundaic species D. haasi Van Roo- pendent sister lineages, and are therefore valid species within ijen and Vogel, 2008 and D. kopsteini Vogel and Van the framework of a lineage-based species concept. However, to conform to current taxonomic practice, the Javan population is Rooijen, 2007 have their northern distributional limits not named separately due to the fact that it is not diagnosable. on the Thai-Malay Peninsula. In addition, Indochinese and Sundaic populations of the widely distributed Dendrelaphis pictus have been shown to be morpho- Contents logically distinct (Vogel and Van Rooijen, 2008). Given the known distribution of D. subocularis and Introduction ...................................................................................... 85 biogeographic importance of the Isthmus of Kra, we Material and methods ..................................................................... 86 were quite surprised to find several museum speci- Results ............................................................................................... 88 mens that had been collected on Java. All had been Discussion ........................................................................................ 89 Acknowledgements ........................................................................ 90 erroneously identified as D. pictus (Gmelin, 1789). References ........................................................................................ 91 These specimens thus represent a population that is isolated by 2000 km from the nearest population on mainland Southeast Asia and that is separated from the Introduction latter by the Isthmus of Kra as well as a sea barrier. In this study, multivariate analyses of morphologi- The colubrid snake Dendrelaphis subocularis (Bou- cal data were used to determine the degree of morpho- lenger, 1888) is widespread in Indochina, the southern- logical divergence between the Javan population and Downloaded from Brill.com10/02/2021 02:38:49PM via free access 86 Van Rooijen & Vogel - A Javan population of Dendrelaphis subocularis the mainland Asia population. The results are evalu- Table 1. List of characters used in this study and their abbrevia- ated in the light of a vicariance-hypothesis and the tions. taxonomic status of the Javan population is discussed abbreviation character within the framework of a lineage-based species con- cept (e.g. De Queiroz, 1998, 2005). EYED horizontal diameter of the eye EYEN distance from anterior border of the eye to posterior border of the nostril Material and methods TAIL tail-length HL length of the head WSNT width of the snout The following material was examined for this study SVL snout-vent length (museum abbreviations follow Leviton et al. (1985)): SEX sex Java: RMNH 6681 (46), RMNH 6681 (60), RMNH VENT number of ventrals SUBC number of subcaudals 6681 (106), RMNH 40107, NMW 23675:7; Vietnam: DOR1 number of dorsal scale rows 1 head-length MNHN 1908.55; BMNH 1921.4.1.15; Myanmar: behind the head CAS 215552, CAS 214124, CAS 215512, CAS DOR2 number of dorsal scale rows at the position of 215721, CAS 233045, CAS 214028, CAS 240762, the middle ventral BMNH 1946.1.6.10; Thailand: FMNH 180040, DOR3 number of dorsal scale rows 1 head-length before the tail FMNH 180039, FMNH 180037, FMNH 180035, SUBL number of infralabials in contact with the first FMNH 180042, FMNH 180038, FMNH 180036, sublabial FMNH 178541, FMNH 169419, BMNH 1974.5184, SL1 number of supralabials BMNH 1938,8.7.53, BMNH 1938,8.7.52, BMNH SL2 number of supralabials touching the eye 1914.5.11.3, BMNH 1974.5185; China: CIB 9061, LOR number of loreals INFR number of infralabials KIZ 75I305. TEMP number of temporals For each examined specimen, 19 characters per- POC number of postoculars taining to body proportions and scalation were re- PARSC number of scales bordering the posterior edge corded (Table 1). In addition, longitude and latitude of the parietal scales were determined for inclusion in an analysis of geo- graphic variation. The coordinates were taken direct- teral corner of the parietal. ly from the field notes or were obtained by translating Specimens were allocated to two Operational locations to coordinates. EYED, EYEN, HL and Taxonomic Units (OTU’s): Indochina and Java. The WSNT were measured with a slide calliper to the characters EYED, EYEN, TAIL, HL, WSNT, VENT, nearest 0.1 mm. EYED and EYEN represent the aver- SUBC, INFR, TEMP and PARSC were subjected to a age of left and right measurements. HL was measured Principal Components Analysis (PCA, e.g. Cramer, from the back of the upper jaw to the tip of the snout. 2003). Other characters were excluded as they exhib- WSNT was measured between the prenasals. SVL ited limited variation. Only specimens with complete was measured to the posterior margin of the anal tails were included, reducing the sample to 26 speci- plate by marking the length on a piece of string and mens. Morphometric variables (EYED-WSNT) were subsequently measuring the position of the mark to first adjusted to a common SVL of 46.5 cm to correct the nearest 0.5 cm. TAIL was measured to the nearest for potential ontogenetic variation between the popu- 0.5 cm by straightening the tail against a ruler. VENT lation samples (e.g. Thorpe, 1975, 1983; How et al., was determined following Dowling’s method (1951). 1996; Turan, 1999). The following allometric equa- SUBC was counted on one side, the terminal scute tion was applied: Xadj = X - β(SVL - SVLmean) where was excluded. The last infralabial was defined as the Xadj is the adjusted value of the morphometric varia- infralabial still covered completely by the last supral- ble; X is the original value; SVL is the snout-vent abial. The first sublabial was defined as the scale that length; SVLmean is the overall mean snout-vent length; starts between the posterior chin shield and the in- β is the coefficient of the linear regression of X fralabials and that borders the infralabials (see Peters, against SVL. The object scores corresponding with 1964: Fig. 7). The posterior most temporal scales those principal components (PC’s) having eigenval- were defined as the scales of which more than half of ues > 1, were subjected to a linear regression analy- the area lies in front of an imaginary line that runs sis. Longitude, latitude, SEX and OTU (the latter two from the apex of the last supralabial to the posterola- in the form of dummy-variables) were included as Downloaded from Brill.com10/02/2021 02:38:49PM via free access Contributions to Zoology, 79 (3) – 2010 87 independent variables. The objective of this analysis and latitude in order to illustrate potential morpho- was to determine whether a discrete morphological logical clines as well as transitions and to check for transition from Indochina to Java was in evidence, deviations from