Contributions to Zoology, 77 (1) – 2008Johan van Rooijen; Gernot Vogel: An investigation into the taxonomy of Dendrelaphis tristis (Daudin, 1803): revalidation of Dipsas schokari (Kuhl, 1820) (Serpentes, Colubridae)

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Discussion

The close phenetic similarity between D. schokari and D. tristis indicates that these taxa are sister species, although a phylogenetic analysis should corroborate this. The interparietal spot, bright in D. tristis and rudimentary in some specimens of D. schokari, in particular suggests a close relationship. This conspicuous character is absent in all congeneric species and presumably represents an apomorphy within these two species. Although sympatric on Sri Lanka and the Western Ghats, these species probably do not occur syntopically. The fact that the distribution of D. schokari is restricted to Sri Lanka and the Western Ghats suggests that it is an inhabitant of tropical forest. The wide distribution of D. tristis in India on the other hand suggests an adaptation to relatively dry and open habitat. The difference in eye-size points in the same direction: the comparatively large eye of D. schokari presumably represents an adaptation to the lower light intensity prevalent in tropical forest habitat. D. schokari may have evolved allopatrically on Sri Lanka. The connections between Sri Lanka and India that came into existence due to Pleistocene lowering of sea levels (e.g. Voris, 2000; Pethiyagoda, 2005) could have enabled D. schokari to disperse into South India, at the same time enabling D. tristis to invade Sri Lanka from India.

The Western Ghats and Sri Lanka together have been designated as one of the biodiversity hotspots of the world (Mittermeier et al., 2005) and are known to host a high level of endemism among reptiles (e.g. Das, 1996; Ishwar et al., 2001; Mittermeier et al., 2005). Recent species descriptions suggest that biodiversity as well as levels of endemism harboured by these areas may be substantially higher than currently known (e.g. Pethiyagoda, 2005; Mendis Wickramasinghe et al., 2007; Mukherjee and Bhupathy, 2007). The resurrection of D. schokari from synonymy highlights the unique biological status of this area. Furthermore, it stresses the shortcomings in our current understanding of Dendrelaphis-systematics, as previously noted (Vogel and Van Rooijen, 2007; Van Rooijen and Vogel, 2008). The systematics of Dendrelaphis are still far from complete. For instance, Leptophis mankas (Bell, 1826) might represent a valid name as indicated in the results-section. Its status will be subjected to further research. One reason for the unsatisfactory status of Dendrelaphis-systematics lies in the fact that most prior taxonomic arrangements were based on rather crude as well as subjective judgements. For example, Meise and Henning (1932) recognized eight species and many subspecies but their criteria remained largely implicit. Since the last major revisions of the genus, the advent of computer-technology and associated development of advanced multivariate techniques have greatly improved possibilities for sophisticated and objective taxonomic analysis. Application of such new techniques will considerably refine the taxonomic dissection of this genus. In addition, the application of species concepts that, more than the biological species concept, reflect evolutionary history (e.g. Frost and Hillis, 1990; Zink and McKitrick, 1995; De Queiroz, 1998) may be expected to have a substantial impact on the systematics of this genus, especially with regard to allopatric populations.