Molecular phylogeny of the family Dicroglossidae (Amphibia: Anura) inferred from complete mitochondrial genomes

Cloning, characterization, and evolutionary patterns of KCNQ4 genes in anurans

Acoustic communication plays important roles in the survival and reproduction of anurans. The perception and discrimination of conspecific sound signals of anurans were always affected by masking background noise. Previous studies suggested that some frogs evolved the high-frequency hearing to minimize the low-frequency noise. However, the molecular mechanisms underlying the high-frequency hearing in anurans have not been well explored. Here, we cloned and obtained the coding regions of a high-frequency hearing-related gene (KCNQ4) from 11 representative anuran species and compared them with orthologous sequences from other four anurans. The sequence characteristics and evolutionary analyses suggested the highly conservation of the KCNQ4 gene in anurans, which supported their functional importance. Branch-specific analysis showed that KCNQ4 genes were under different evolutionary forces in anurans and most anuran lineages showed a generally strong purifying selection. Intriguingly, one significantly positively selected site was identified in the anuran KCNQ4 gene based on FEL model. Positive selection was also found along the common ancestor of Ranidae and Rhacophoridae as well as the ancestral O. tianmuii based on the branch-site analysis, and the positively selected sites identified were involved in or near the N-terminal ion transport and the potassium ion channel functional domain of the KCNQ4 genes. The present study revealed valuable information regarding the KCNQ4 genes in anurans and provided some new insights for the underpinnings of the high-frequency hearing in frogs.

How Does Mitochondrial Protein-Coding Gene Expression in Fejervarya kawamurai (Anura: Dicroglossidae) Respond to Extreme Temperatures?

Unusual climates can lead to extreme temperatures. Fejervarya kawamurai, one of the most prevalent anurans in the paddy fields of tropical and subtropical regions in Asia, is sensitive to climate change. The present study focuses primarily on a single question: how do the 13 mitochondrial protein-coding genes (PCGs) respond to extreme temperature change compared with 25 °C controls? Thirty-eight genes including an extra tRNA-Met gene were identified and sequenced from the mitochondrial genome of F. kawamurai. Evolutionary relationships were assessed within the Dicroglossidae and showed that Dicroglossinae is monophyletic and F. kawamurai is a sister group to the clade of (F. multistriata + F. limnocharis). Transcript levels of mitochondrial genes in liver were also evaluated to assess responses to 24 h exposure to low (2 °C and 4 °C) or high (40 °C) temperatures. Under 2 °C, seven genes showed significant changes in liver transcript levels, among which transcript levels of ATP8, ND1, ND2, ND3, ND4, and Cytb increased, respectively, and ND5 decreased. However, exposure to 4 °C for 24 h was very different in that the expressions of ten mitochondrial protein-coding genes, except ND1, ND3, and Cytb, were significantly downregulated. Among them, the transcript level of ND5 was most significantly downregulated, decreasing by 0.28-fold. Exposure to a hot environment at 40 °C for 24 h resulted in a marked difference in transcript responses with strong upregulation of eight genes, ranging from a 1.52-fold increase in ND4L to a 2.18-fold rise in Cytb transcript levels, although COI and ND5 were reduced to 0.56 and 0.67, respectively, compared with the controls. Overall, these results suggest that at 4 °C, F. kawamurai appears to have entered a hypometabolic state of hibernation, whereas its mitochondrial oxidative phosphorylation was affected at both 2 °C and 40 °C. The majority of mitochondrial PCGs exhibited substantial changes at all three temperatures, indicating that frogs such as F. kawamurai that inhabit tropical or subtropical regions are susceptible to ambient temperature changes and can quickly employ compensating adjustments to proteins involved in the mitochondrial electron transport chain.

Phylogeny of spiny frogs Nanorana (Anura: Dicroglossidae) supports a Tibetan origin of a Himalayan species group

Recent advances in the understanding of the evolution of the Asian continent challenge the long-held belief of a faunal immigration into the Himalaya. Spiny frogs of the genus Nanorana are a characteristic faunal group of the Himalaya-Tibet orogen (HTO). We examine the phylogeny of these frogs to explore alternative biogeographic scenarios for their origin in the Greater Himalaya, namely, immigration, South Tibetan origin, strict vicariance. We sequenced 150 Nanorana samples from 62 localities for three mitochondrial (1,524 bp) and three nuclear markers (2,043 bp) and complemented the data with sequence data available from GenBank. We reconstructed a gene tree, phylogenetic networks, and ancestral areas. Based on the nuDNA, we also generated a time-calibrated species tree. The results revealed two major clades (Nanorana and Quasipaa), which originated in the Lower Miocene from eastern China and subsequently spread into the HTO (Nanorana). Five well-supported subclades are found within Nanorana: from the East, Central, and Northwest Himalaya, the Tibetan Plateau, and the southeastern Plateau margin. The latter subclade represents the most basal group (subgenus Chaparana), the Plateau group (Nanorana) represents the sister clade to all species of the Greater Himalaya (Paa). We found no evidence for an east-west range expansion of Paa along the Himalaya, nor clear support for a strict vicariance model. Diversification in each of the three Himalayan subclades has probably occurred in distinct areas. Specimens from the NW Himalaya are placed basally relative to the highly diverse Central Himalayan group, while the lineage from the Tibetan Plateau is placed within a more terminal clade. Our data indicate a Tibetan origin of Himalayan Nanorana and support a previous hypothesis, which implies that a significant part of the Himalayan biodiversity results from primary diversification of the species groups in South Tibet before this part of the HTO was uplifted to its recent heights.

The revised complete mitogenome sequence of the tree frog Polypedatesmegacephalus (Anura, Rhacophoridae) by next-generation sequencing and phylogenetic analysis

The mitochondrial genome (mitogenome) sequence of the tree frog Polypedates megacephalus (16,473 bp) was previously reported as having the unusual characteristic of lacking the ND5 gene. In this study, a new mitogenome of P. megacephalus (19,952 bp) was resequenced using the next-generation sequencing (NGS) and standard Sanger sequencing technologies. It was discovered that the ND5 gene was not lost but translocated to the control region (CR) from its canonical location between the ND4 and ND6 genes. In addition, a duplicated control region was found in the new mitogenome of this species. Conservative region identification of the ND5 gene and phylogenetic analysis confirmed that the ND5 gene was located between two control regions. The phylogenetic relationship among 20 related species of anura revealed a rearrangement of the ND5 gene during the evolutionary process. These results also highlighted the advantages of next-generation sequencing. It will not only decrease the time and cost of sequencing, but also will eliminate the errors in published mitogenome databases.

Complete mitochondrial genome of a kind of snakehead fish Channa siamensis and its phylogenetic consideration

The snakehead fish, Channa siamensis, belongs to the genus of Channa (perciformes: Channidae) and was first reported by Günther in 1861. Despite it has been described approximately for 15 decades, the genetic information is limited and the taxon status of this kind of fish is still unclear. The primary objective of this study is to get more genomic data and calculate the taxon location of this kind of fish. The next generation sequencing method was used to obtain the whole mitochondrial DNA information, and bioinformatic analysis was performed to investigate the evolutionary status and taxon location of C. siamensis. The circular mitochondrial DNA was 16,570 bp in length, and which showed typical piscine structure and arrangement. The overall nucleotide composition was 29.28% A, 24.72% T, 30.71% C, 15.29% G, with 54.1% AT, respectively. Phylogenetic analyses using concatenated amino acid and nucleotide sequences of the 13 protein-coding genes with two different methods (Maximum likelihood and Bayesian analysis) both highly supported C. siamensis belongs to the genus Channa and shows a close relationship with C. micropeltes. These data will provide more useful information for a better understanding of the mitochondrial genomic diversities and evolution in fish as well as novel genetic markers for studying population genetics and species identification.