Phylogeny of lamniform sharks based on whole mitochondrial genome sequences

• Main Author: Ferrara, Toni Laura
• Format: Text
• Language: English
• Published: Iowa State University Digital Repository 2003
• Subjects: Ecology; evolution and organismal biology; Zoology; Cetorhinus maximus; Porbeagle
• Online Access: https://lib.dr.iastate.edu/rtd/19960; https://lib.dr.iastate.edu/cgi/viewcontent.cgi?article=20959&context=rtd

The order Lamniformes (Chondrichthyes: Elasmobranchii: Neoselachii) contains 15 living species of sharks organized into seven families. This group includes the notorious great white shark (Carcharodon carcharias), and four closely related species in the genera Lamna (porbeagle, salmon shark) and Isurus (mako sharks). Also in this order are the thresher sharks (Alopias spp.), notable for their elongated tails; the sand tiger sharks, grouped in two genera (Odontaspis and Carcharias); two harmless filter-feeders, the basking shark (Cetorhinus maximus) and megamouth shark (Megachasma pelagios); the small-sized crocodile shark (Pseudocarcharias kamoharai); and the bizarre goblin shark (Mitsukurina owstoni). An overview of the biology, systematics, morphology and fossil record of these sharks is presented. Previous investigations of lamniform phylogeny, using both anatomical and molecular-based data, have been unable to resolve relationships within this group. In an effort to elucidate lamniform phylogeny, this study examined the entire mitochondrial genome sequence for all living species in this order. Mitochondrial genomes for all 15 lamniform species were sequenced, and both individual genes and multigene datasets were analyzed using several standard phylogenetic methods (maximum parsimony, maximum likelihood, and distance optimality criteria). Overall, the current study recovered the same relationships as previous molecular studies. The clade Lamnidae is strongly supported, although internal relationships could not be resolved. Carcharias and Cetorhinus were frequently allied with the Lamnidae, especially for multigene datasets, but results were variable for individual genes and depended on the method employed. There was no support for a monophyletic Odontaspididae (Carcharias+Odontaspis). A clade ("AMOP") comprising of Alopias, Megachasma, Odontaspis, and Pseudocarcharias was frequently recovered in this study, but relationships within this clade could not be resolved further. As in previous molecular studies, the genus Alopias proved to be especially problematic. The majority of analyses recovered Mitsukurina as either the basal outgroup to all other lamniforms or the sister taxon to the AMOP clade. Based on the current study of all living lamniforms, complete taxon sampling and larger datasets do not necessarily provide a better phylogeny. Finally, a large tandem duplication is documented for the mitochondrial genome Mitsukurina owstoni.