The Evolution Of The Mitochondrial Genome And Its Phylogeny In The Genus Acropora

Animal mitochondrial genomes are covalently closed circular double-stranded DNA molecules.Due to the characteristics such as low molecular weight,conserved gene content and organization,minimal intergenic region,dominantly maternal inheritance and lack of recombination,they have been widely employed in the research fields of molecular ecology(e.g.,conservation genetics,phygeography,behavioral ecology and phylogenetics).Mitochondrial genomes of Hymenopteran insects are normally extraordinarily rich in AT contents,which has rendered difficult the mtDNA sequencing and assembly and thus has negatively influenced relevant mitogenomic studies.Despite the family Formicidae being a taxon-rich group within Hymenoptera,only 15 ant species from 11 genera and three subfamilies have been publicly reported for their mitochondrial genomes to date.The genus Acropyga(Hymenoptera:Formicidae:Formicinae)represents a group of ant species which live under the ground.In the present study,14 Acropyga species were characterized for their mitochondrial genomes,and further assays were carried out.The major findings are summarized as follows:(1)The mitochondrial genomes of Acropyga ants are circular closed double-stranded DNA molecules,and harbor the typical panel of 37 mitochondrial genes(incl.17 protein-coding genes/PCGs,22 tRNAs and 2 rRNAs)and a noncoding control region.The gene arrangement is highly conserved among the congeners,and is identical to that of four previously published mitochondrial genomes(i.e.Formica fusca,Formica selysi,Leptomyrmex pallens&Linephithema humile).(2)Mitochondrial PCGs in these 14 Acropyga species are all initiated with the ATN codons,and are terminated with TAA,TAG or the incomplete stop codon TA/T.For three species(A.arnoldi,A.fuhrmanni&A.smithii),a 10-bp intergenic region is present between the two adjacent PCGs atp6 and atp8;for the remaining 11 species,this intergenic region is only 7 bp in length.(3)Phylogenetic analyses were conducted based on the maximum-likelihood(ML)and Bayesian Inference(BI)analyses of the concatenated sequences of 12 PCGs.The topology of the phylogenetic tree supported the current subfamily-level taxonomic framework of the three subfamilies Formicinae,Dolichoderinae and Myrmicinae,and also suggested the monophyly of the genus Acropyga.(4)Frame shift induced by single nucleotide insertion was detected in the mitochondrial PCG nad5 for two Acropyga species(A.arnoldi&A.silvestrii).Considering that these two closely related ants together formed a single subclade in the phylogenetic tree,such a phenomenon may have significant phylogenetic implications.