Systematics of the Genus Alopias (Lamniformes: Alopiidae) with Evidence for the Existence of an Unrecognized Species

Abstract

Allozymic variation for 13 presumptive loci was used to infer phylogenetic relationships among geographic samples of thresher sharks of the genus Alopias. The existence of an unrecognized species of Alopias was suggested by the allozymic data. Trees were constructed from allozymic data using maximum-parsimony and Distance Wagner procedures. The coding procedure used in maximum-parsimony analysis united all samples of A. superciliosus and A. pelagicus into a single Operational Taxonomic Unit (OTU). Maximum-parsimony analysis identified a single most parsimonious tree that united the unrecognized species of Alopias and the A. superciliosus + A. pelagicus OTU into a clade excluding A. vulpinus. The Distance Wagner analysis united samples of A. vulpinus into a clade excluding samples of all other species; the unrecognized species of Alopias and A. vulpinus constituted a clade; and samples of A. superciliosus and A. pelagicus were united into a clade. Analyses of maximum-parsimony and Distance Wagner trees using FREQPARS showed that the maximum-parsimony tree was shorter. Some uncertainty regarding phylogenetic placement of the unrecognized species remained because the synapomorphy uniting this species into a clade with A. superciliosus and A. pelagicus was scorable only in a single specimen of the unrecognized species. Allozymic data were not sufficient to accurately determine relationships among different geographic samples of A. superciliosus and A. pelagicus. This may have resulted from the low number of specimens and loci examined and/or the high genetic similarity of these two species. A high proportion of potentially informative polyallelic loci was found within Alopias; however, the outgroup (Isurus oxyrinchus) did not possess character states found among ingroup forms for many of these loci. Allozymes do show promise for investigating phylogenetic relationships of sharks at the genus/species level provided the number of species (OTUs) is relatively low, an informative outgroup is used, and the high proportion of potentially informative loci found in this