Speciation of silverside Chirostoma attenuatum (Pisces: Atheriniformes) in Central Mexico

The high speciation rate of Chirostoma in Central Mexico has been associated with allopatric speciation events promoted by the emergence of vicariant barriers in freshwater habitats, as well as by sympatric ecological segregation, common in those species inhabiting lacustrine ecosystems. Through nuclear and mitochondrial markers, this study revealed a speciation process within Chirostoma attenuatum resulting in two evolutionary independent units that coincide with their morphological differentiation, indicating that Chirostoma attenuatum and Chirostoma zirahuen may be considered separate species. This process was the result of vicariance associated with geological dynamics of the region. Phylogeographic findings indicated two speciation stages: early allopatric isolation, during which the isolated populations accumulated unique adaptations, and secondary contact with low migration rate and the maintenance of the evolutionary trajectory. Historical demographic analysis indicated that the two well-differentiated lineages underwent independent evolutionary histories in their respective lakes. Chirostoma zirahuen from Zirahuen and C.attenuatum from Patzcuaro represent unique and irreplaceable genetic diversity that must to be conserved.