Studies on Pakistan Reptiles Pt. 1. The Genus Echis (Viperidae)

Abstract

This is the first of a series of studies intended to analyze the geographic patterns in the meristic characters of Pakistan reptiles. This part concerns the saw-scated vipers, Echis carinatus. The scales analyzed are numbers of ventrals, subcaudals, dorsal rows, rows of oblique dorsals, gulars, suboculars and supraoculars; color patterns include number of dorsal spots, ventral pattern, infralabials, lateral body and head. Maps of geographic variation in the means of each of these characters are provided and the patterns of variation within Pakistan are discussed. Each of the characters studied tends to have a different geographic distribution of mean values. However, one recurrent pattern is a rapid change in character state between Iranian Plateau populations (Chagai area, Pakistan) and those of the Quetta highland area. Coastal populations are also rather distinctive, but are generally similar to those in the Indus River Plain. Himalayan foothill populations are often similar to those of coastal areas, suggesting that these geographical peripheral populations are also peripheral in regard to genetic adaptation. In the Indus River Delta, populations can be subdivided into several distinct subgroups. The resulting mosaic of character states is attributed to historic factors concerned with changing positions of the deltaic distributaries during geologic time. Finally, the population in the Cholistan-Thar Desert at the Indo-Pakistan border is distinctive in both color and scalation. These differences are probably adaptive responses to local arid conditions. Several character states of this population and that in the Chagai Desert of northwest Pakistan are convergent. Of those climatic factors believed important within the adaptive mileau of this species, mean daily maximum and minimum temperatures during June and July (when they are most active) are considered most important. Some of the population differences probably reflectadaptations to water and heat loss. Contrary to recently published opinion, we conclude there is only one species of saw-scaled viper in Pakistan; its scientific name is Echis carinatus. Within Pakistan we recognize three distinct geographic races--E.c. multisquamatus Cherlin, E. c. sochureki Stemmler and E. c. astolae Mertens. The geographic distribution of characters analyzed shows that the major barrier to gene flow between E. c. sochureki and E. c. multisquamatus is the central north-south massif (Sulaiman Range, et al.). For E. c. sochureki and E. c. astolae it is the Arabian Sea, and for E. c. sochureki and E. c. carinatus (Indian Peninsula) it is largely a matter of overall distance. In general, the race E. c. sochureki is intermediate between E. c. multisquamatus and E. c. carinatus.