The phylogeny of coleoid cephalopods inferred from molecular evolutionary analyses of the cytochrome c oxidase I, muscle actin, and cytoplasmic actin genes
Although the fossil record of early cephalopods is rich and demonstrates the dominance of the group in Paleozoic times, the mainly soft-bodied coleoids (Cephalopoda: Coleoidea) are poorly represented. Therefore, little is known of the evolutionary history of coleoids through paleontology and current...
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| Format: | Others |
| Language: | English |
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W&M ScholarWorks
1998
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| Online Access: | https://scholarworks.wm.edu/etd/1539616597 https://scholarworks.wm.edu/cgi/viewcontent.cgi?article=2165&context=etd |
| Summary: | Although the fossil record of early cephalopods is rich and demonstrates the dominance of the group in Paleozoic times, the mainly soft-bodied coleoids (Cephalopoda: Coleoidea) are poorly represented. Therefore, little is known of the evolutionary history of coleoids through paleontology and current classifications of the subclass are based primarily on the morphology of extant representatives. A molecular phylogenetic analysis of the Coleoidea was therefore warranted. Phylogenetic relationships within the Coleoidea were constructed using molecular sequence data from one mitochondrial and two nuclear genes: cytochrome c oxidase I (COI) and two unlinked actin genes (Actin I and Actin II, respectively). A 657 base-pair portion of the COI gene was examined for 55 coleoid taxa encompassing a broad spectrum of diversity in the subclass. The COI gene exhibited the most rapid evolutionary rate among the three genes examined. Eighty-two sequences from a 784 base-pair portion of three paralogous actin genes were obtained from 44 terminal taxa. The Actin I gene was highly conserved and provided information for determining deep-level relationships. The Actin II gene was intermediately conserved and exhibited a broad range of sequence divergence than the COI and Actin I genes. The evolution of the actin gene family in cephalopods was compared to that in other molluscs, protostomes, and deuterostomes. Analyses of actin gene family evolution provided evidence that the Actin I gene encodes a muscle-type of actin, and that the Actin II gene encodes a cytoplasmic actin. These analyses also supported at least two independent derivations of muscle-type actins during the evolution of the protostome lineage. The following conclusions were drawn from the results of phylogenetic analyses: (1) the cephalopod subclass Coleoidea is monophyletic; (2) the order Octopoda is monophyletic and is sister group to the monotypic order Vampyromorpha; (3) the Decapodiformes, consisting of the orders Teuthoidea and Sepioidea, is monophyletic; (4) the orders Teuthoidea and Sepioidea are polyphyletic; (5) the teuthoid suborders Myopsida and Oegopsida are monophyletic and polyphyletic, respectively; (6) the Myopsida and the oegopsid families Chtenopterygidae and Bathyteuthidae are more closely related to the sepioid families Spirulidae, Sepiidae, and Sepiolidae, than they are to other teuthoid groups. |
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