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The Yucatan Peninsula (YP) suffered several marine transgressions and regressions during the Quaternary, thus molding the distribution of its present biota, especially its freshwater fish fauna. The Mayan cichlid (Mayaheros urophthalmus Günther) isa euryhaline fish native to the Atlantic slope of Mexico and northern Central America, including the YP; it is one of the most widespread freshwater species in the region. Herein we discuss a phylogeographic scenario by which the Mayan cichlid may have reached its current distribution in the YP. A Bayesian analysis and minimum spanning network were inferred from two partial mitochondrial genes, Cytochrome b (CYTB) and Cytochrome c Oxidase I (COI). The two fragments showed genetic differentiation among populations (Fst=0.31, p value <0.001). Tajima's D and Fu 's F revealed a tendency to the expansion of some populations. A consistent ordination of north vs south populations was observed. A spatial analysis of molecular variance (SAMOVA) was performed torecognize putative barriers among populations of M. urophthalmus. A secondary molecular calibration located the window time in which the dispersal event may have occurred during the Pleistocene, around 1 Mya. We determined that a Quaternary dispersal around the old coastlines from the south explains the current distribution of the Mayan cichlid. Inglés

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