Evolutionary relationships of pupfishes in the Cyprinodon eximius complex (Atherinomorpha : Cyprinodontiformes)

Allozymes encoded by 30 presumptive gene loci were used in phylogenetic ana lyses of the Cyprinodon eximius complex (Cyprinodontidae), a group of 12 sp ecies occurring primarily on the Mexican Plateau from the states of Zacatec as and Nuevo Leon north to the Rio Grande, The most parsimonious phylogenet ic tree supported the following: (1) the C. eximius complex is paraphyletic , with a clade comprising C. alvarezi and C. ceciliae from the Potosi and S andia basins being basal relative to the pupfishes examined (including five species from outside the C. eximius complex); (2) an early event separated the Rio Conchos-Rio Grande-Old Rio Nazas pupfishes from a previously ident ified clade of eight species (the "western pupfishes") that extends from th e Guzman Basin in northwestern Chihuahua to the Death Valley system of Cali fornia; (3) the ancestral C, meeki, a species from the Pacific slope, was i solated from pupfishes in the Old Rio Nazas by a Pleistocene stream capture ; (4) C. nazas, a species from the headwaters of the Old Rio Nazas is parap hyletic with respect to C. atrorus, one of two species from Cuatro Cienegas (this supports one of the three suggested outlets of the Old Rio Nazas to the Rio Grande, i.e., the Rio Salado); (5) a clade of four species occupies the Rio Conchos drainage in Mexico and contiguous waters of the Rio Grande drainage (this clade includes the relatively wide-ranging C. eximius and t hree local endemics from spring systems in Chihuahua, C. macrolepis and C. pachycephalus, and the Pecos River in Texas, C. elegans); and (6) the two p upfishes from Cuatro Cienegas, C. atrorus and C. bifasciatus, represent div ergent lineages, the latter apparently being a relatively early product of pupfish evolution on the Mexican Plateau.