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The complete mitochondrial genome of the sea spider Achelia bituberculata (Pycnogonida, Ammotheidae): arthropod ground pattern of gene arrangement.

Park SJ, Lee YS, Hwang UW - BMC Genomics (2007)

Bottom Line: This controversy has recently been rekindled by differences in the conclusions based on neuroanatomical data concerning the chelifore and the patterns of Hox expression.Phylogenetic analyses based on mitochondrial protein-coding genes showed that Pycnogonida may be authentic arachnids (= aquatic arachnids) within Chelicerata sensu lato, as indicated by the name 'sea spider,' and suggest that the Cormogonida theory - that the pycnogonids are a sister group of all other arthropods - should be rejected.However, in view of the relatively weak node confidence, strand-biased nucleotide composition and long-branch attraction artifact, further more intensive studies seem necessary to resolve the exact position of the pycnogonids.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Biology, Teachers College, Kyungpook National University, Daegu 702-701, Korea. shinju@knu.ac.kr

ABSTRACT

Background: The phylogenetic position of pycnogonids is a long-standing and controversial issue in arthropod phylogeny. This controversy has recently been rekindled by differences in the conclusions based on neuroanatomical data concerning the chelifore and the patterns of Hox expression. The mitochondrial genome of a sea spider, Nymphon gracile (Pycnogonida, Nymphonidae), was recently reported in an attempt to address this issue. However, N. gracile appears to be a long-branch taxon on the phylogenetic tree and exhibits a number of peculiar features, such as 10 tRNA translocations and even an inversion of several protein-coding genes. Sequences of other pycnogonid mitochondrial genomes are needed if the position of pycnogonids is to be elucidated on this basis.

Results: The complete mitochondrial genome (15,474 bp) of a sea spider (Achelia bituberculata) belonging to the family Ammotheidae, which combines a number of anatomical features considered plesiomorphic with respect to other pycnogonids, was sequenced and characterized. The genome organization shows the features typical of most metazoan animal genomes (37 tightly-packed genes). The overall gene arrangement is completely identical to the arthropod ground pattern, with one exception: the position of the trnQ gene between the rrnS gene and the control region. Maximum likelihood and Bayesian inference trees inferred from the amino acid sequences of mitochondrial protein-coding genes consistently indicate that the pycnogonids (A. bituberculata and N. gracile) may be closely related to the clade of Acari and Araneae.

Conclusion: The complete mitochondrial genome sequence of A. bituberculata (Family Ammotheidae) and the previously-reported partial sequence of Endeis spinosa show the gene arrangement patterns typical of arthropods (Limulus-like), but they differ markedly from that of N. gracile. Phylogenetic analyses based on mitochondrial protein-coding genes showed that Pycnogonida may be authentic arachnids (= aquatic arachnids) within Chelicerata sensu lato, as indicated by the name 'sea spider,' and suggest that the Cormogonida theory - that the pycnogonids are a sister group of all other arthropods - should be rejected. However, in view of the relatively weak node confidence, strand-biased nucleotide composition and long-branch attraction artifact, further more intensive studies seem necessary to resolve the exact position of the pycnogonids.

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Translocation of trnQ between the 12S rRNA (rrnS) and control region (CR) observed in a sea spider, Achelia bituberculata, two terrestrial spiders, Ornithictinus huwena and Habronattus oregonensis, and a collembolan, Tetrodontophora bielanensis. Compared to the typical arthropod trnI-trnQ-M arrangement between nad2 and the CR, the trnQ gene in A. bituberculata is found between rrnS and the CR. Such trnQ translocation appears in the two terrestrial spiders, O. huwena and H. oregonensis, and in a collembolan, T. bielanensis. Refer to the Fig. 1 legend for abbreviations of components. The Q position is highlighted with an asterisk (*) and a yellow box. Bold underlines indicate the reversed orientation of gene transcription.
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Figure 3: Translocation of trnQ between the 12S rRNA (rrnS) and control region (CR) observed in a sea spider, Achelia bituberculata, two terrestrial spiders, Ornithictinus huwena and Habronattus oregonensis, and a collembolan, Tetrodontophora bielanensis. Compared to the typical arthropod trnI-trnQ-M arrangement between nad2 and the CR, the trnQ gene in A. bituberculata is found between rrnS and the CR. Such trnQ translocation appears in the two terrestrial spiders, O. huwena and H. oregonensis, and in a collembolan, T. bielanensis. Refer to the Fig. 1 legend for abbreviations of components. The Q position is highlighted with an asterisk (*) and a yellow box. Bold underlines indicate the reversed orientation of gene transcription.

Mentions: The trnQ gene in A. bituberculata is located between rrnS and the control region (CR). It is found between trnIand trnM in most arthropods [38]. Comparisons among the trnQ positions in arthropods (Fig. 3) show that the rrnS-trnQ-CR arrangement in pycnogonids is also found in the jumping spider Habronattus oregonensis (Araneae, Salticidae) [47] and in a collembolan, Tetrodontophora bielanensis [48]. A similar pattern (rrnS-trnI-trnQ-CR) is also observed in the Chinese earth tiger spider Ornithoctonus huwena (Araneae, Theraphosidae) [47]. However, collembolans and spiders are not closely related, and another terrestrial spider (Heptathela) and another collembolan (Gomphiocephalus hodgsoni) have the Limulus-like arthropod ground pattern (trnI-trnQ-trnM). Thus, the rrnS-trnQ-CR arrangement found in a pycnogonid (A. bituberculata), a collembolan (T. bielanensis) and two terrestrial spiders (H. oregonensis and O. huwena) is likely to be homoplastic. Further intensive comparative studies are needed to examine whether the rrnS-trnQ-CR pattern is indeed a homoplastic feature or an important phylogenetic marker.


The complete mitochondrial genome of the sea spider Achelia bituberculata (Pycnogonida, Ammotheidae): arthropod ground pattern of gene arrangement.

Park SJ, Lee YS, Hwang UW - BMC Genomics (2007)

Translocation of trnQ between the 12S rRNA (rrnS) and control region (CR) observed in a sea spider, Achelia bituberculata, two terrestrial spiders, Ornithictinus huwena and Habronattus oregonensis, and a collembolan, Tetrodontophora bielanensis. Compared to the typical arthropod trnI-trnQ-M arrangement between nad2 and the CR, the trnQ gene in A. bituberculata is found between rrnS and the CR. Such trnQ translocation appears in the two terrestrial spiders, O. huwena and H. oregonensis, and in a collembolan, T. bielanensis. Refer to the Fig. 1 legend for abbreviations of components. The Q position is highlighted with an asterisk (*) and a yellow box. Bold underlines indicate the reversed orientation of gene transcription.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2194727&req=5

Figure 3: Translocation of trnQ between the 12S rRNA (rrnS) and control region (CR) observed in a sea spider, Achelia bituberculata, two terrestrial spiders, Ornithictinus huwena and Habronattus oregonensis, and a collembolan, Tetrodontophora bielanensis. Compared to the typical arthropod trnI-trnQ-M arrangement between nad2 and the CR, the trnQ gene in A. bituberculata is found between rrnS and the CR. Such trnQ translocation appears in the two terrestrial spiders, O. huwena and H. oregonensis, and in a collembolan, T. bielanensis. Refer to the Fig. 1 legend for abbreviations of components. The Q position is highlighted with an asterisk (*) and a yellow box. Bold underlines indicate the reversed orientation of gene transcription.
Mentions: The trnQ gene in A. bituberculata is located between rrnS and the control region (CR). It is found between trnIand trnM in most arthropods [38]. Comparisons among the trnQ positions in arthropods (Fig. 3) show that the rrnS-trnQ-CR arrangement in pycnogonids is also found in the jumping spider Habronattus oregonensis (Araneae, Salticidae) [47] and in a collembolan, Tetrodontophora bielanensis [48]. A similar pattern (rrnS-trnI-trnQ-CR) is also observed in the Chinese earth tiger spider Ornithoctonus huwena (Araneae, Theraphosidae) [47]. However, collembolans and spiders are not closely related, and another terrestrial spider (Heptathela) and another collembolan (Gomphiocephalus hodgsoni) have the Limulus-like arthropod ground pattern (trnI-trnQ-trnM). Thus, the rrnS-trnQ-CR arrangement found in a pycnogonid (A. bituberculata), a collembolan (T. bielanensis) and two terrestrial spiders (H. oregonensis and O. huwena) is likely to be homoplastic. Further intensive comparative studies are needed to examine whether the rrnS-trnQ-CR pattern is indeed a homoplastic feature or an important phylogenetic marker.

Bottom Line: This controversy has recently been rekindled by differences in the conclusions based on neuroanatomical data concerning the chelifore and the patterns of Hox expression.Phylogenetic analyses based on mitochondrial protein-coding genes showed that Pycnogonida may be authentic arachnids (= aquatic arachnids) within Chelicerata sensu lato, as indicated by the name 'sea spider,' and suggest that the Cormogonida theory - that the pycnogonids are a sister group of all other arthropods - should be rejected.However, in view of the relatively weak node confidence, strand-biased nucleotide composition and long-branch attraction artifact, further more intensive studies seem necessary to resolve the exact position of the pycnogonids.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Biology, Teachers College, Kyungpook National University, Daegu 702-701, Korea. shinju@knu.ac.kr

ABSTRACT

Background: The phylogenetic position of pycnogonids is a long-standing and controversial issue in arthropod phylogeny. This controversy has recently been rekindled by differences in the conclusions based on neuroanatomical data concerning the chelifore and the patterns of Hox expression. The mitochondrial genome of a sea spider, Nymphon gracile (Pycnogonida, Nymphonidae), was recently reported in an attempt to address this issue. However, N. gracile appears to be a long-branch taxon on the phylogenetic tree and exhibits a number of peculiar features, such as 10 tRNA translocations and even an inversion of several protein-coding genes. Sequences of other pycnogonid mitochondrial genomes are needed if the position of pycnogonids is to be elucidated on this basis.

Results: The complete mitochondrial genome (15,474 bp) of a sea spider (Achelia bituberculata) belonging to the family Ammotheidae, which combines a number of anatomical features considered plesiomorphic with respect to other pycnogonids, was sequenced and characterized. The genome organization shows the features typical of most metazoan animal genomes (37 tightly-packed genes). The overall gene arrangement is completely identical to the arthropod ground pattern, with one exception: the position of the trnQ gene between the rrnS gene and the control region. Maximum likelihood and Bayesian inference trees inferred from the amino acid sequences of mitochondrial protein-coding genes consistently indicate that the pycnogonids (A. bituberculata and N. gracile) may be closely related to the clade of Acari and Araneae.

Conclusion: The complete mitochondrial genome sequence of A. bituberculata (Family Ammotheidae) and the previously-reported partial sequence of Endeis spinosa show the gene arrangement patterns typical of arthropods (Limulus-like), but they differ markedly from that of N. gracile. Phylogenetic analyses based on mitochondrial protein-coding genes showed that Pycnogonida may be authentic arachnids (= aquatic arachnids) within Chelicerata sensu lato, as indicated by the name 'sea spider,' and suggest that the Cormogonida theory - that the pycnogonids are a sister group of all other arthropods - should be rejected. However, in view of the relatively weak node confidence, strand-biased nucleotide composition and long-branch attraction artifact, further more intensive studies seem necessary to resolve the exact position of the pycnogonids.

Show MeSH
Related in: MedlinePlus