The mitochondrial genome of Conus textile, coxI-coxII intergenic sequences and Conoidean evolution

Abstract

The cone snails belong to the superfamily Conoidea, comprising approximately 10,000 venomous marine gastropods. We determined the complete mitochondrial DNA sequence of Conus textile. The gene order is identical in Conus textile, Lophiotoma cerithiformis (another Conoidean gastropod), and the neogastropod Ilyanassa obsoleta, (not in the superfamily Conoidea). However, the intergenic interval between the coxI and coxII genes was much longer in C. textile (165bp) than in any other previously analyzed gastropod. We used the intergenic region to evaluate evolutionary patterns. In most neogastropods and three conidean families the intergenic interval is small (<30 nucleotides). Within Conus, the variation is from 130 to 170bp, and each different clade within Conus has a narrower size distribution. In Conasprella, a subgenus traditionally assigned to Conus, the intergenic regions vary between 200 and 500bp, suggesting that the species in Conasprella are not congeneric with Conus. The intergenic region was used for phylogenetic analysis of a group of fish-hunting Conus, despite the short length resolution was better than using standard markers. Thus, the coxI-coxII intergenic region can be used both to define evolutionary relationships between species in a clade, and to understand broad evolutionary patterns across the large superfamily Conoidea.

Figure 1

Gene arrangement of Conus textile mitochondrial DNA. Each tRNA gene is identified by the one letter amino acid code. The serine and leucine tRNA genes are identified by the first letter of the codon family (in parenthesis) that their transcription products recognize. The central arrow indicates the direction of transcription of proteins and rRNA genes. The direction of transcription of the tRNA genes are indicated by arrows. Numbers at gene boundaries indicate apparently non-coding nucleotides between genes. Overlap of genes are indicated by a minus sign preceding the numbers. The solid black sectors indicate the longest non-coding regions.

Figure 2

Comparison of phylogenetic trees constructed using MrBayes and coxI-coxII intergenic sequences (A) and 16s mitochondrial DNA sequences (B). (Only those branches that were found in 75% or more of the trees were retained. Shells for each species are also shown in A.

Figure 3

Phylogenetic relationship of Conoideans constructed using MrBayes and 16s mitochondrial rRNA sequences. Members of the Drillidae, Turridae, Terebridae, Conidae (four clades), Conasprella and the “Daphellid genera” (see text) are represented.