XX (ZS70&x,^ 



Bull. nut. Hist. Mus. Lond, (Zool.) 68(2): 107-11 



Issued 28 November 2002 



A contribution to the systematics of two 

 commonly confused pitvipers from the Sunda 

 Region: Trimeresurus hageni and T. 

 sumatranus 



K. L. SANDERS, A. MALHOTRA AND R. S. THORPE 



School of Biological Sciences, University of Wales, Bangor, Gwynedd LL57 2UW, Wales, UK. 



SYNOPSIS. The systematics of two Southeast Asian green pitviper species, Trimeresurus hageni and T. sumatranus, are investi- 

 gated by canonical variate analysis. Preliminary results reveal two morphological forms corresponding to mainly T. hageni in West 

 Malaysia, Thailand and Singapore and T. sumatranus in Borneo. Allopatric populations of both taxa are examined from Sumatra. 

 Geographic variation is present in both species, which are distinguished mainly by head scalation. but also by colour and pattern. 



INTRODUCTION 



Trimeresurus sumatranus (Raffles, 1822) and T. hageni (Lidth de 

 Jeude, 1886) are closely related species, occupying low elevations 

 in undisturbed forests and having largely overlapping ranges. The 

 systematics of these species and their precise distribution is an area 

 of long-standing confusion. Many workers assign both species to T. 

 sumatranus by default (Tweedie, 1983; Lim, 1991; Jintakune, 1995; 

 David and Vogel, 1996) and the status of T. hageni has been in 

 dispute since its initial description (Lidth de Jeude, 1886; Lidth de 

 Jeude, 1890;Boulenger, 1896; Brongersma, 1933). 



T. hageni was described as a separate species from T. sumatranus on 

 the basis that only one or two supralabial scales are in contact with the 

 subocular (compared with three in T. sumatranus), and the dark edges 

 on head and body scales and dorsal cross-bands that are characteristic 

 of T. sumatranus are not present (Lidth de Jeude, 1 886). The species' 

 distribution is widely debated, but specimens from south Thailand, 

 West Malaysia and Singapore are normally assigned to T. hageni, and 

 specimens from Borneo are normally assigned to T. sumatranus 

 (David and Vogel, 1996; Cox et al., 1998;StuebingandInger, 1999), 

 but see Dring (1979) who placed specimens in the NHM collections 

 from West Malaysia, southern Thailand and Sarawak in T. sumatranus. 

 Both species are thought to occur on Sumatra and surrounding islands 

 (Brongersma, 1933; Dring etai, 1989; Cox elai., 1998). 



There have been few attempts to resolve the systematics of T. 

 hageni and T. sumatranus since their initial description; these have 

 been based on small sample sizes and a traditional character-by- 

 character approach (Boulenger, 1896; Brongersma, 1933). Given 

 the levels of geographic, ontogenetic and sexual variation usually 

 present in viper species (Wiister et al., 1992; Malhotra and Thorpe, 

 1997), the systematics of these taxa is best approached using modern 

 statistical methods based on a broad range of morphological 

 characters. In this paper, we present preliminary results from an 

 ongoing investigation of the systematics and interrelationships of T. 

 hageni and T. sumatranus. 



MATERIALS AND METHODS 



We examined 78 specimens from museum collections in the United 

 States, Europe and Malaysia (Figure 1). A total of 93 characters 



relating to scalation, colour and pattern were recorded for each 

 specimen. Ventral scales were counted from head to vent, with the 

 first ventral identified according to the method of Dowling ( 1951 ). 

 The positions of scale reductions along the body (recorded as the 

 number of the ventral or subcaudal scale opposite which it was 

 situated) were transformed to percentage ventral scale (%VS) or 

 caudal scale (%CS) position, in order to compensate for variation in 

 ventral and subcaudal scale number. Male and female specimens 

 were treated separately in all analyses to avoid bias caused by sexual 

 dimorphism. 



Specimens were grouped by locality into operational taxonomic 

 units (OTUs). Two groups dominated the analysis, one was com- 

 prised of specimens from Thailand. West Malaysia and Singapore, 

 and another was comprised of specimens from Borneo (Sabah and 

 Sarawak). These groups were shown to be monophyletic by mole- 

 cular analysis (unpublished data), which revealed a clear 

 distinction between western specimens that lacked dorsal cross- 

 bands and had at most two supralabials connected to the subocular 

 scale, and eastern specimens that had dorsal cross-bands and had 

 three supralabials in contact with the subocular scale. Molecular 

 data was not available for specimens from Sumatra, and these 

 were grouped individually to avoid combining sympatric species 

 in one OTU. 



Each OTU was checked prior to further analysis using Princi- 

 pal Component Analysis, which does not require that individuals 

 be assigned groups prior to the analysis. The integrity of the 

 OTUs was confirmed with the exception of one specimen from 

 Betong (south Thailand), which had dark banding and in the PCA 

 ordination was closest to the Borneo OTU. In subsequent analysis 

 this specimen was grouped separately from the other western 

 specimens. The OTUs used and their sample size for each sex is 

 listed in Table 1. 



Variation between OTUs was tested for individual characters by 

 means of one-way analysis of variance (ANOVA). Only characters 

 showing significant between-OTU variation were used in subse- 

 quent analyses. These are presented in Table 2. 



Canonical variate analysis (CVA) was used to investigate patterns 

 of geographic variation between OTUs. This method maximises the 

 separation between groups relative to variation within groups. It is a 

 standard multivariate method and has been applied successfully to 

 numerous models of geographic variation in reptiles (Wiister et al., 

 1992; Thorpe et al., 1994; Daltry et ai, 1996). 



© The Natural History Museum. 2002 



