MOLECULAR PHYLOGENY AND EVOLUTION OF THE DEEP-SEA FISH GENUS STERNOPTYX

A portion of mitochondrially encoded 12S and 16S ribosomal RNA genes w ere sequenced from all four valid species of the midwater deep-sea fis h genus Sternoptyx (Teleostei: Sternoptychidae) and four sternoptychid outgroup taxa. Secondary structure-based alignment resulted in a char acter matrix consisting of 865 bp of unambiguously aligned, combined s equences of the two genes, which were subjected to phylogenetic analys es using the maximum parsimony and maximum likelihood methods. The res ultant tree topologies from the two methods were congruent and support ed by various tree statistics. Although the single most parsimonious t ree was not statistically different from the two second parsimonious t rees, independent morphological evidence from the anal fin pterygiopho re configuration and associated structures strongly supported the form er as the preferred hypothesis. Mapping of the contemporary geographic distribution patterns of the four species onto the tree suggested tha t there was a common ancestor of Sternoptyx with a circumglobal distri bution, which had been subdivided into southern and northern ancestral populations along 30 degrees S, possibly through some large-scale oce anographic event. There has been no discernible speciation event in th e southern population, though the northern population has subsequently speciated into three contemporary species with largely allopatric/mic roallopatric distributions. (C) 1998 Academic Press.