Phylogenetic utility of the tyrosine kinase gene X-src for assessing relationships among representative cichlid fishes

The nuclear gene X-src is a member of the tyrosine-kinase class of proto-on cogenes whose normal product is localized within the cytoplasm of the cell. The X-src gene has been used in only a few phylogenetic studies, each focu sing on systematics of killifishes (Cyprinodontiformes), The present study is an attempt to examine the phylogenetic utility of X-src for uncovering r elationships of representative cichlid fishes, especially the cichlids of M iddle America, The family Cichlidae is a species-rich group of tropical fre shwater fish made up of more than 1000 species which show a Gondwanan patte rn of distribution. Cichlid fish have been the focus of numerous studies ra nging from behavioral to biogeographical to systematic in nature, Particula r emphasis has focused on the cichlids of the African Great Lakes and the e xplosive adaptive radiation of this group. However, Neotropical cichlids ha ve received considerably less attention than their African counterparts. Ou r findings regarding the utility of X-src concur with those of previous phy logenetic analyses showing the exons of X-src to be highly conserved and us eful mostly for revealing deep relationships among taxa. Like previous X-sr c studies, we also found the intron sequences of the gene to be variable in length and difficult to align across distantly related taxa but they provi ded useful information for resolving relationships among more closely relat ed taxa. The X-src phylogeny supports the monophyly of Neotropical cichlids and cichlasomines groups A( =heroines) + B (=cichlasomines), A highly reso lved tree is obtained within the heroines but little support is evident for most nodes based on the low number of unambiguous substitutions. The X-src gene is likely to be quite useful for resolving deep phylogenetic relation ships such as those among major groups of actinopterygian fishes. (C) 2000 Academic Press.