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Open Access Research article

A complete mitochondrial genome sequence of the wild two-humped camel (Camelus bactrianus ferus): an evolutionary history of camelidae

Peng Cui23, Rimutu Ji1, Feng Ding23, Dan Qi23, Hongwei Gao4, He Meng4, Jun Yu2, Songnian Hu2* and Heping Zhang1*

Author Affiliations

1 Key Laboratory of Dairy Biotechnology and Engineering Ministry of Education, College of Food Science and Engineering, Inner Mongolia Agricultural University, Huhhot, China

2 Key Laboratory of Genome Information and Sciences, Beijing Institute of Genomics, Chinese Academy of Sciences, Beijing, China

3 Graduated School of the Chinese Academy of Sciences, Beijing, China

4 School of Agriculture and biology, Shanghai Jiao Tong University, Shanghai, China

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BMC Genomics 2007, 8:241  doi:10.1186/1471-2164-8-241

Published: 18 July 2007

Abstract

Background

The family Camelidae that evolved in North America during the Eocene survived with two distinct tribes, Camelini and Lamini. To investigate the evolutionary relationship between them and to further understand the evolutionary history of this family, we determined the complete mitochondrial genome sequence of the wild two-humped camel (Camelus bactrianus ferus), the only wild survivor of the Old World camel.

Results

The mitochondrial genome sequence (16,680 bp) from C. bactrianus ferus contains 13 protein-coding, two rRNA, and 22 tRNA genes as well as a typical control region; this basic structure is shared by all metazoan mitochondrial genomes. Its protein-coding region exhibits codon usage common to all mammals and possesses the three cryptic stop codons shared by all vertebrates. C. bactrianus ferus together with the rest of mammalian species do not share a triplet nucleotide insertion (GCC) that encodes a proline residue found only in the nd1 gene of the New World camelid Lama pacos. This lineage-specific insertion in the L. pacos mtDNA occurred after the split between the Old and New World camelids suggests that it may have functional implication since a proline insertion in a protein backbone usually alters protein conformation significantly, and nd1 gene has not been seen as polymorphic as the rest of ND family genes among camelids. Our phylogenetic study based on complete mitochondrial genomes excluding the control region suggested that the divergence of the two tribes may occur in the early Miocene; it is much earlier than what was deduced from the fossil record (11 million years). An evolutionary history reconstructed for the family Camelidae based on cytb sequences suggested that the split of bactrian camel and dromedary may have occurred in North America before the tribe Camelini migrated from North America to Asia.

Conclusion

Molecular clock analysis of complete mitochondrial genomes from C. bactrianus ferus and L. pacos suggested that the two tribes diverged from their common ancestor about 25 million years ago, much earlier than what was predicted based on fossil records.