Genetic differentiation of the southern population of the fathead minnow Pimephales promelas Rafinesque (Actinopterygii: Cyprinidae)

Background: Mexico is one of the most megadiverse countries in the world, with considerable reaches and endemicity in the diversity of fishes compared to other countries and regions. Recent phylogenetic studies in co-distributed species of widespread fishes, besides revealing a subestimation of species richness in the Mesa del Norte, in Mexico, suggest phylogenetic congruence in some species complexes. Previous morphological and meristic analyses concluded that at least three subspecies of Pimephales promelas exist in United States populations, suggesting that the richness in Pimephales could be underestimated. But no studies have examined the morphologic and genetic diversity in Southern populations of Pimephales promelas . We presented analyses of the genetic variation among P. promelas populations across its Southern distributional range. Methods: . Phylogenetic reconstruction and genetic distances using cytochrome b and S7 sequences were done. Results: . The results based on phylogenetic trees, species tree, genetic distances and haplotype networks revealed the existence of at least four well-differentiated lineages (Yaqui Lineage, Nazas+Conchos Lineage, Santa Maria Lineage and Casas Grandes Lineage). Discussion: The four well supported lineages found confirm Pimephales promelas as a species complex. Composition and distribution of these major lineages is also consistent with previous biogeographic hypothesis for other fishes in the region, supporting the fragmentation of the ancestral Lake Cabeza de Vaca, possibly due to the combined influence of tectonic events and increasing regional aridity, as well as events of interchange between basins via stream capture.