Abstract
Cynoglossus monopus, a small benthic fish, belongs to the Cynoglossidae, Pleuronectiformes. It was rarely studied due to its low abundance and cryptical lifestyle. In order to understand the mitochondrial genome and the phylogeny in Cynoglossidae, the complete mitogenome of C. monopus has been sequenced and analyzed for the first time. The total length is 16,425 bp, typically containing 37 genes with novel gene rearrangements. The tRNA-Gln gene is inverted from the light to the heavy strand and translocated from the downstream of tRNA-Ile gene to its upstream. The control region (CR) translocated downstream to the 3’-end of ND1 gene adjoining to inverted to tRNA-Gln and left a 24 bp trace fragment in the original position. The phylogenetic trees were reconstructed by Bayesian inference (BI) and maximum likelihood (ML) methods based on the mitogenomic data of 32 tonguefish species and two outgroups. The results support the idea that Cynoglossidae is a monophyletic group and indicate that C. monopus has the closest phylogenetic relationship with C. puncticeps. By combining fossil records and mitogenome data, the time-calibrated evolutionary tree of families Cynoglossidae and Soleidae was firstly presented, and it was indicated that Cynoglossidae and Soleidae were differentiated from each other during Paleogene, and the evolutionary process of family Cynoglossidae covered the Quaternary, Neogene and Paleogene periods.
Highlights
Flatfishes (Pleuronectiformes) are unique animals with both eyes moved on one side of the body through asymmetrical development
This study suggests that mitochondrial gene rearrangement in Cynoglossidae is a single originated evolutionary event, which occurred in the common ancestor of Cynoglossus and Paraplagusia before at least 22.82 Mya (17.11–28.44 Mya)
The highly similar rearranged gene order in all available Cynoglossus and Paraplagusia species [18,35,36,37,38,39,40,41,42,43,44,45] inferred that novel gene order possesses some selective advantage in this group, kept it conserved in the whole lineage
Summary
Flatfishes (Pleuronectiformes) are unique animals with both eyes moved on one side of the body through asymmetrical development. Cynoglossus monopus belongs to Cynoglossidae in suborder Soleoidei, distributed from the Malay Archipelago to the Indian Ocean, including the west and northward along the South China Sea [1,2]. It is a small benthic fish with ctenoid scale covered on both-side, two lateral line on ocular-side and absent lateral line on blind-side. The Cynoglossidae was believed to be derived from the Soleidae as well, and have a closer relationship with Soleidae than Achiridae [5] In morphology, both eyes of the species in Cynoglossidae and Soleidae turned to the left-side and the right-side, respectively, which is the principle basis to distinguish these two families [1]. The genera Cynoglossus and Paraplagusia were sister groups belonging to subfamily Cynoglossinae, while Symphurus was the only genus in subfamily Symphurinae [3]
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