Molecular systematics of Middle American cichlid fishes and the evolution of trophic-types in 'Cichlasoma (Amphilophus)' and 'C. (Thorichthys)'.

The majority of Middle American cichlids are placed in the informal assemblage 'Cichlasoma.' The group is divided into eight sections which appear to be based primarily on trophic morphology. Although several members of 'Cichlasoma' have been used in ecomorphological, behavioral, and biogeographic studies, no phylogenetic hypotheses for the group exist. In an attempt to develop a better understanding of the phylogenetic relationships of 'cichlasomine' cichlids, we examined the evolution of the trophic specialization, substratum-sifting, in two sections, 'Cichlasoma (Thorichthys)' and 'C. (Amphilophus),' to determine whether the trait reflects common ancestry. We sequenced the complete mitochondrial cytochrome b gene for 19 cichlids representing six sections of 'Cichlasoma,' and representatives of other Neotropical Cichlidae. Additional cichlid, and noncichlid outgroup sequences were included for a total of 22 taxa. The molecular phylogeny supports the recognition of the section 'C. (Thoricthys)' as a natural group, and we place those cichlids in the genus Thorichthys. The phylogeny also depicts 'C. (Amphilophus)' as paraphyletic, with substratum-sifters and generalized predators forming separate nonsister clades. We recommend that the substratum-sifting clade of the section 'C. (Amphilophus)' be placed in the resurrected genus Astatheros. The generalized predator clade of 'C. (Amphilophus)' contains only two species, 'C. (A.) citrinellum' and 'C. (A.) labiatum,' which we place in the genus Amphilophus. The phylogenetic hypotheses generated indicate that the substratum-sifting genera Thorichthys and Amphilophus do not share a common ancestor. Reconstruction of the evolution of substratum-sifting is equivocal, requiring either the independent evolution of the trait on two separate occasions or its presence in a more inclusive clade and subsequent loss in nonsubstratum sifting species.