Southern Mexican minnows of the genus Notropis (Actinopterygii, Cyprinidae): genetic variation, phylogenetic relationships and biogeographical implications

Allozyme analyses were performed to determine patterns of genetic variation and phylogenetic relationships within the genus Notropis in southern Mexic o. Products of 28 gene loci were resolved in 24 geographic samples belongin g to four putative species. These species represent the southern limit of t he Cyprinidae in North America. Five loci were found monomorphic and 11 Mer e diagnostic among species when the outgroup. Phoxinus phoxinus, was not ta ken into account. Four groups were identified. but these do not correspond perfectly to the four nominal species, Notropis sallaei was identified by a llozyme analyses being the most basal among southern Mexican Notropis and t he most genetically divergent. Notropis imeldae. was also diagnosed on the basis of allozymic variation, however a population sample representing the Balsas drainage was genetically divergent and is considered as an undescrib ed new species (N. n. sp.). No genetic differences were found between the s amples of N. boucardi and iii. moralesi. Therefore. we recommend that N. mo ralesi should be considered as a junior synonym of;N. boucardi. A broad geo graphic sampling strategy was employed across all the distribution range of N. boucardi representing rivers from three different drainages, which cove r both Mexican slopes. The slight divergence found among the headwater popu lations of hi. boucardi permitted us to predict a model of paleohydrographi c relationships of these three drainages. Two alternative hypotheses are po stulated to explain the current distribution pattern of populations of N. b oucardi in southern Mexico. (C) 2001 Elsevier Science Ltd. All rights reser ved.