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 as semblage 'Cichlasoma.' The group is divided into eight sections which appear to be based primarily on trophic morphology. Although several m embers of 'Cichlasoma' have been used in ecomorphological, behavioral, and biogeographic studies, no phylogenetic hypotheses for the group e xist. In an attempt to develop a better understanding of the phylogene tic relationships of 'cichlasomine' cichlids, we examined the evolutio n of the trophic specialization, substratum-sifting, in two sections, 'Cichlasoma (Thorichthys)' and 'C. (Amphilophus),' to determine whethe r the trait reflects common ancestry. We sequenced the complete mitoch ondrial cytochrome b gene for 19 cichlids representing six sections of 'Cichlasoma,' and representatives of other Neotropical Cichlidae. Add itional 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. (Amp hilophus)' as paraphyletic, with substratum-sifters and generalized pr edators forming separate nonsister clades. We recommend that the subst ratum-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 phylogen etic hypotheses generated indicate that the substratum-sifting genera Thorichthys and Amphilophus do not share a common ancestor. Reconstruc tion of the evolution of substratum-sifting is equivocal, requiring ei ther the independent evolution of the trait on two separate occasions or its presence in a more inclusive clade and subsequent loss in nonsu bstratum sifting species. (C) 1997 Academic Press.