Genetic distances among fishes of the genus Siganus (Siganidae) from the Western Pacific Ocean

Frequencies of electromorphs encoded by 14 polymorphic loci were used to estimate genetic distances among samples of the rabbitfishes Siganus argenteus, S. doliatus, S. fuscescens, S. guttatus, S. javus, S. punctatus, S. randalli, S. spinus, S. vermiculatus, and S. (Lo) vulpinus. Samples of the surgeonfish Naso lituratus (Acanthuridae) were included in the electrophoretic survey for the purpose of outgroup comparison. A matrix of genetic-distance estimates was used for construction of dendrograms by neighbor-joining, complete-linkage and single-linkage procedures, and the unweighted pair-group method of arithmetic averages (UPGMA). Cluster analysis revealed interspecific relationships that are concordant with several predictions intimated in the most recent taxonomic revision of this assemblage of fishes. S. randalli and S. vermiculatus, the pair postulated to be sibling species on the basis of strikingly similar external morphology, were found to exhibit the lowest levels of genetic divergence relative to all other pairs of study species. S. randalli, S. guttatus, and S. vermiculatus comprised one of three clusters discerned in all resultant topologies (i.e., ball clusters). S. argenteus, S. fuscescens, and S. spinus, three fusiform-bodied species, formed a second ball cluster that was clearly separable from the remainder of the siganids studied (which are all relatively deep-bodied). A third ball cluster contained S. punctatus and S. vulpinus: S. doliatus was depicted as being allied with S. punctatus and S. vulpinus in the neighbor-joining and complete-linkage topologies but not in topologies generated by UPGMA and single linkage. It is noteworthy that S. punctatus, S. vulpinus, and S. doliatus are the only three species included in the present study which purportedly school when young but form pair-bonds as adults. In all topologies, S. javus occupied branches stemming from furcation points between fusiform-bodied and deep-bodied species. Of all the siganids studied, S. argenteus was found to be least divergent genetically from N. lituratus. S. argenteus is the only siganid known to spawn pelagic eggs and undergo a specialized pelagic stage (features typical within the Acanthuridae). Hence, genetic relationships within the Siganidae and among the Siganidae and a representative acanthurid coincide with a host of predictions stemming from morphologic and life-history studies of the Acanthuroidei.