Phylogeography and monophyly of the swordtail fish species Xiphophorus birchmanni (Cyprinodontiformes, Poeciliidae)

" We used sequences of the mitochondria control region to assess the distribution of genetic variation within and among populations of the poeciliid fish species Xiphophorus birchmanni. We collected 122 X. birchmanni samples from 11 sites in three drainage systems comprising the distribution of the species. We found low levels of polymorphism among aligned sequences and low levels of genetic variation within populations but high levels of genetic differentiation among populations. Haplotypes are exclusive to three river drainages (Los Hules, Calabozo and San Pedro). Mantel tests revealed correlations between geographical (both straight-line and river distances) and genetic distance, consistent with an isolation by distance scenario, while nested clade analysis suggested allopatric fragmentation between haplotypes from two of the major drainages, and isolation by distance with restricted gene flow within those drainages. Finally, monophyly of X. birchmanni is strongly supported while the previous hypothesis of the evolutionary origin of this species from X. malinche is not "