A VARIATIONAL ANALYSIS OF POPULATIONS OF BOTHROPS (SERPENTES, VIPERIDAE) FROM WESTERN VENEZUELA

Character variation was analyzed with univariate and multivariate meth ods in populations of Bothrops from the Andean piedmont (N = 37) and n earby upper llanos (N = 19) communities of western Venezuela in an are a of suspected sympatry between Bothrops atrox and B. asper. In an atr ox-asper affinity gradient created with four currently-used specific d iagnostic characters, 80% of the specimens were intermediate, and no c haracter suite or single character separated the snakes into two discr ete taxonomic units. Specimens from these populations represent one sp ecies, B. atrox, rather than two sympatric ones. Character variation i n these populations is complex, and a summary table of sexual, ontogen etic, and geographical relations to variation of 13 characters is pres ented. An elevational and geographical trend exists in several size-in dependent characters; a greater frequency of rectangular to trapezoida l blotches, tendencies to heavier ventral mottling, and higher interoc ular number are observed in the piedmont population than in the llanos , where trends to contrasting character states occur. These character states are discordant in specimens of each population. We hypothesize that such phenotypic differentiation is related to different biotic se lection regimes associated with the llanos and piedmont communities. A previously described species, Bothrops isabelae Sandner-Montilla, fro m this area in Venezuela is recognized as a synonym of Bothrops atrox. Results from our study suggest that such comprehensive populational s tudies have more potential than a traditional range-wide variational a pproach for resolution of the atrox-asper problem.