Complete Mitogenome of Spottail Spiny Turbot, Psettodes belcheri (Pleuronectiformes:Psettodidae): Characterization and Phylogeny

Abstract

Psettodes belcheri (Bennett, 1831) is known as the primitive flatfish distributed in Eastern Atlantic, starting from Western Sahara and Mauritania to Angola. In this study, we provide the complete mitogenome of Psettodes belcheri from Cameroon using the next-generation sequencing. The mitogenome of Psettodes belcheri (16,747 bp) consists of 37 genes, including 13 protein-coding genes, 2 ribosomal RNA genes, 22 transfer RNA genes, and control region. The Psettodes belcheri mitogenome displays an AT-biased (54.15%), which is similar to its congener, Psettodes erumei (53.07% and 53.61%). Most protein-coding genes (PCGs) in Psettodes belcheri start with an ATG start codon, with the exception of Cytochrome Oxidase I (COI), which initiates with a GTG codon. Additionally, four PCGs use TAA as their stop codon, while seven PCGs have an incomplete stop codon. Two PCGs, NAD1 and NAD6, terminate with AGG and TAG stop codons, respectively. In the mitogenome of Psettodes belcheri, most transfer RNAs (tRNAs) exhibit typical cloverleaf secondary structures, except for tRNA-serine, which lacks a DHU arm. Comparative analysis of the conserved blocks within the control regions of two Psettodidae species reveals that the CSB-II block is more extensive (51 base pairs) than other blocks and contains highly variable sites. A comprehensive phylogenetic analysis, using the concatenated sequences of 13 mitochondrial protein- coding genes, classifies various Pleuronectiformes species. It highlights the Psettodidae family's basal position and demonstrates the monophyletic clustering of Psettodes species. The estimated divergence time between Psettodes belcheri and Psettodes erumei is approximately 20.56 million years ago, shedding light on their separation and colonization during the early Miocene. The TimeTree analysis also estimates the divergence of the two suborders, Psettodoidei and Pleuronectoidei, occurring during the late Paleocene to early Eocene, around 56.87 million years ago. The distribution patterns of Psettodes flatfishes are influenced by ocean currents and environmental conditions, which contribute to their ecological speciation.