Genetic evidence for reproductive isolation of the recently described unicornfish Naso caesius and its sibling N. hexacanthus

Abstract

The recently described unicornfish, Naso caesius (Acanthuridae; subfamily Nasinae), was distinguished from a very similar congener, N. hexacanthus, by differences in tongue, body and lower lip coloration, shape of the pair of bladelike caudal spines, and presence or absence of a black border on the opercle and preopercle. We describe the biochemical genetics of these geminate species from fish collected arround Guam, Southern Marianas. We found: (1) a fixed allelic difference at the locus encoding muscle creatine kinase (CK-A ^*); (2) “private” [i.e., found in one operational taxonomic unit (OTU) but not in the other] alleles in relatively high frequency at the locus encoding lactate dehydrogenase (LDH-A ^*); and (3) significantly different allele frequencies at a locus encoding aspartate aminotransferase (AAT-2 ^*) and at LDH-A ^* and PGM ^*. Our detection of diagnostic electrophoretic markers contrasts with results of an allozymic survey mentioned in the original description of N. caesius. The fixed allelic difference among operational taxonomic units collected in sympatry provides a further taxonomic criterion by which N. caesius and N. hexacanthus can be distinguished. The absence of electrophoretically recognizable hybrids provides evidence that N. caesius and N. hexacanthus are reproductively isolated within our study area.