mtDNA gene sequence, allozyme, and morphological uniformity among red diamond rattlesnakes,Crotalus ruberandCrotalus exsul

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Abstract
Genetic and morphological diversity were investigated in two species of red diamond rattlesnakes. Crotalus exsul Garman, 1884 occurs on Isla de Cedros, and Crotalus ruber Cope, 1892 is found on the peninsula of Baja California, in southern California, and on many islands in the Gulf of California. A partial sequence consisting of 297 nucleotide base pairs from cytochrome b of the mitochondrial DNA genome revealed a single difference only, a level of variation common between rattlesnake subspecies. A phylogenetic analysis showed C. exsul to possess the derived state. The products of 29 gene loci were resolved using horizontal starch gel electrophoresis. No fixed differences were observed to occur, although gene frequencies at one locus, catalase-A, were significantly different (P < 0.00004). Among the 16 morphological characters gathered, none served to unequivocally identify the two taxa. The results of a principal components analysis, using eight morphological characters, revealed that the characters of the Isla de Cedros specimens represented a small subset found in the peninsular Baja California specimens. A multivariate discriminate function analysis could correctly identify 94% of C. ruber and 83% of C. exsul. Because of the close similarity among these two taxa, we believe the red diamond rattlesnakes are best considered a single species, C. exsul, and the peninsular population retained as C. e. ruber; one Gulf of California population is recognized as C. e. lorenzoensis.