A recent study of the molecular phylogeny of poeciliid fishes indicates that the family colonised Central America multiple times over the last 65 million years.
Publishing in a recent issue of the journal Molecular Phylogenetics and Evolution, Tomas Hrbek, Jens Seckinger and Axel Meyer studied the molecular phylogeny of the Poeciliinae, a subfamily of the Poeciliidae using data of 15 mitochondrial and one nuclear gene.
The results of the analysis show that the livebearing fish family Poeciliidae colonised Central America via dispersal multiple times in the course of the last 65 million years.
The authors state that: "A late Cretaceous connection between Middle and South America appears to have existed, in principle allowing bi-directional dispersal betwen north and south.
"Poeciliids are an ancient group initially restricted to its South American area of origin, that have undergone an additional vicariance-driven radiation in Nuclear Central America, the Greater Antilles and Southern Central America.
"The main colonization of Middle and North America most likely occurred through Greater Antilles around the time of the Eocene"Oligocene transition."
The authors also found that some genera (Heterandria, Poecilia) were not monophyletic, and that the traditional placement of poeciliines by Rosen and Bailey into eight tribes is not supported by their study, implying that the taxonomy of poeciliines should be carefully re-examined.
According to the authors: "Three of the original eight tribes are monotypic. Monophyly of the three of the five remaining tribes is rejected statistically in our analyses..."
The authors also offer some insight as to why their results do not agree with the traditional taxonomy of these livebearers : "The characters used to place individual species into genera and genera into tribes...evidently have evolved multiple times, possibly in response to similar ecological pressures or due to sexual selection...
"Hence, many of the gonopodial similarities of species that are currently assigned to, based on our study, polyphyletic tribes are therefore presumably largely attributable to homoplasy and cannot serve as taxonomically reliable characters."
For more information, see the paper: Hrbek, T, J Seckinger and A Meyer (2007) A phylogenetic and biogeographic perspective on the evolution of poeciliid fishes. Molecular Phylogenetics and Evolution 43, 986"998.