Vol. 56, 2017
Loss and Gain of Group I Introns in the Mitochondrial Cox1 Gene of the Scleractinia (Cnidaria; Anthozoa)
Yaoyang Chuang1,2, Marcelo Kitahara3,4, Hironobu Fukami5, Dianne Tracey6, David J. Miller3,7,*, and Chaolun Allen Chen1,2,*
1Biodiversity Research Center, Academia Sinica,
Nankang, Taipei 115, Taiwan
(Received 19 January 2017; Accepted 12 April 2017)
Yaoyang Chuang, Marcelo Kitahara, Hironobu Fukami, Dianne Tracey, David J. Miller, and Chaolun Allen Chen (2017) Group I introns encoding a homing endonuclease gene (HEG) that is potentially capable of sponsoring mobility are present in the cytochrome oxidase subunit 1 (cox1) gene of some Hexacorallia, including a number of scleractinians assigned to the “robust” coral clade. In an effort to infer the evolutionary history of this cox1 group I intron, DNA sequences were determined for 12 representative “basal” and “complex” corals and for 11 members of the Corallimorpharia, a sister order of the Scleractinia. Comparisons of insertion sites, secondary structures, and amino acid sequences of the HEG implied a common origin for cox1 introns of corallimorpharians, and basal and complex corals, but cox1 introns of robust corals were highly divergent, most likely reflecting independent acquisition. Phylogenetic analyses with a calibrated molecular clock suggested that cox1 introns of scleractinians and corallimorpharians have persisted at the same insertion site as that in the common ancestor 552 million years ago (mya). This ancestral intron was probably lost in complex corals around 213 mya in the junction between the Permian and Triassic. The coral cox1 gene remained intronless until new introns, probably from sponges or fungi, reinvaded different positions of the cox1 gene in robust corals around 135 mya in the Cretaceous, and then it subsequently began to lose them around 65.5 mya in some robust coral lineages coincident with the later Maastrichtian extinction at the Cretaceous-Tertiary boundary.
Key words: Group I intron,Cytochrome oxidase I, Scleractinian, Corallimorpharian, Mass extinction.
*Correspondence: Tel: 886-2-27899549. E-mail: firstname.lastname@example.org (CA Chen); email@example.com (DJ Miller).