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.