The mitochondrial genome sequence of Enterobius vermicularis (Nematoda: Oxyurida)--an idiosyncratic gene order and phylogenetic information for chromadorean nematodes

The complete mitochondrial genome sequence was determined for the human pinworm Enterobius vermicularis (Oxyurida: Nematoda) and used to infer its phylogenetic relationship to other major groups of chromadorean nematodes. The E. vermicularis genome is a 14,010-bp circular DNA molecule that encodes 36 genes (12 proteins, 22 tRNAs, and 2 rRNAs). This mtDNA genome lacks atp8, as reported for almost all other nematode species investigated. Phylogenetic analyses (maximum parsimony, maximum likelihood, neighbor joining, and Bayesian inference) of nucleotide sequences for the 12 protein-coding genes of 25 nematode species placed E. vermicularis, a representative of the order Oxyurida, as sister to the main Ascaridida+Rhabditida group. Tree topology comparisons using statistical tests rejected an alternative hypothesis favoring a closer relationship among Ascaridida, Spirurida, and Oxyurida, which has been supported from most studies based on nuclear ribosomal DNA sequences. Unlike the relatively conserved gene arrangement found for most chromadorean taxa, E. vermicularis mtDNA gene order is very unique, not sharing similarity to any other nematode species reported to date. This lack of gene order similarity may represent idiosyncratic gene rearrangements unique to this specific lineage of the oxyurids. To more fully understand the extent of gene rearrangement and its evolutionary significance within the nematode phylogenetic framework, additional mitochondrial genomes representing a greater evolutionary diversity of species must be characterized.     

The mitochondrial genomes of Cambaroides similis and Procambarus clarkii (Decapoda: Astacidea: Cambaridae): the phylogenetic implications for Reptantia

Kim, S., Park, M.‐H., Jung, J.‐H., Ahn, D.‐H., Sultana, T., Kim, S., Park, J.‐K., Choi, H.‐G. & Min, G.‐S. (2012). The mitochondrial genomes of Cambaroides similis and Procambarus clarkii (Decapoda: Astacidea: Cambaridae): the phylogenetic implications for Reptantia. —Zoologica Scripta, 41, 281–292. We determined the complete mitochondrial (mt) genome sequences of two northern hemisphere freshwater crayfish species, Cambaroides similis and Procambarus clarkii (Decapoda: Astacidea: Cambaridae). These species have an identical gene order with typical metazoan mt genome compositions. However, their gene arrangement was very distinctive compared with the pan‐crustacean ground pattern because of the presence of a long inverted block, which included 19 coding genes and a control region (CR). Because the CR was inverted, their nucleotide frequencies showed a reversed strand‐specific bias compared with the other decapods. Based on a comparative analysis of mt genome arrangements between southern and northern hemisphere crayfish and their putative close marine relative (Homarus americanus, a true clawed lobster), we postulated that the ancestor of freshwater crayfish had a typical pan‐crustacean mtDNA gene order, similar to its marine relatives. Based on this assumption, we traced the most parsimonious gene rearrangement scenario of the northern hemisphere crayfish. In a phylogenetic study on the infraordinal relationships in reptan decapods, the lineage Lineata [Thalassinidea (Brachyura, Anomura)] was well supported, while the infraorder positions of Achelata and Astacidea remained unidentified.