Molecular systematics of the genus Allodontichthys (Cyprinodontiformes: Goodeidae)

" Phylogenetic analyses of cytochrome c oxidase subunit I (627bp) and mitochondrial control region (338bp aligned) sequences for all known species of Allodontichthys were performed. Allodontichthys was recovered as monophyletic, and A. hubbsi was supported as the most primitive member of the genus in all analyses. Combined data analyses suggest that A. polylepis is sister to a clade comprising A. tamazulae and A. zonistius; however, a strict consensus of COI and control region cladograms results in a collapse of this node. The two species that are broadly sympatric, A. hubbsi and A. tamazulae, are not sister taxa. Allodontichthys was found the sister group of a clade including Ilyodon and Xenotaenia. These three genera are the only goodeids to occupy high-gradient river systems. Ilyodon and Allodontichthys share similar distributions; however, Allodontichthys exhibits greater than an order of magnitude more genetic variation in COI than Ilyodon in comparisons of individuals from the same localities in the Ameca and Armeria drainage systems. This is interpreted to mean Allodontichthys arrived in some western drainages significantly before Ilyodon. The Rio Coahuayana appears to be the center of origin of the genus Allodontichthys. This river basin contains the most primitive member of the genus, and appears to have connected with the Mesa Central, the center of endemism of the Goodeidae. A calibrated rate of molecular change in COI reveals Allodontichthys began diverging approximately 6.2 million years ago (mya). Remaining speciation in the group appears to have occurred about 2.7 to 3.3 mya. The hypothesis that a “hard” polytomy comprising A. zonistius, A. polylepis, and A. tamazulae could be explained by speciation of A. polylepis and A. tamazulae from different A. zonistius ancestors is presented. Stream capture is evident but not frequent in the history of Allodontichthys, and speciation does not clearly correlate with documented geologic activity of the Mexican Transvolcanic Belt "