Comparative analysis of the mitogenomes of two Corydoras (Siluriformes, Loricarioidei) with nine known Corydoras, and a phylogenetic analysis of Loricarioidei

Insights into phylogenetic positions and distribution patterns: Complete mitogenomes of two sympatric Asian horned toads in Boulenophrys (Anura: Megophryidae)

Boulenophrys sangzhiensis and Boulenophrys tuberogranulata, two narrow-distributed toad species within the Megophryidae family in southern China, are experiencing population declines due to habitat loss and degradation. Despite their critical conservation status, the two species remain largely overlooked in public and scientific spheres. This study presented the first sequencing, assembly, and annotation of the complete mitogenomes of both species using next-generation sequencing. The mitogenome of B. sangzhiensis was 16,950 bp, while that of B. tuberogranulata was 16,841 bp, each comprising 13 protein-coding genes (PCGs), 22 transfer RNA genes (tRNAs), two ribosomal RNA genes (rRNAs), and a noncoding control region (D-loop). The gene content, nucleotide composition, and evolutionary rates of each mitogenome were analyzed. Both mitogenomes exhibited negative AT skew and GC skew with high A + T content. ATP8 exhibited the highest evolutionary rate, while COI had the lowest. A phylogenetic analysis based on 28 mitogenomes revealed two major clades of Megophryidae, supporting the classification of two subfamilies, Megophryinae and Leptobrachiinae. Within the subfamily Megophryinae, the genus Boulenophrys was divided into two species groups. Intriguingly, despite coexisting in Zhangjiajie City, B. sangzhiensis and B. tuberogranulata exhibited distinct origins from the two different species groups, underscoring the unique role of the coexisting area Zhangjiajie in driving their speciation and preserving their current populations. A parallel pattern was also identified in the Leptobrachiinae genus Leptobrachium within the same region. This study provided valuable data references and enhanced our understanding of the molecular characteristics of these threatened amphibian species.

The complete mitochondrial genome of Pethia padamya (Actinopteri, Cyprinidae)

Pethia padamya (Kullander and Britz, 2008) is a freshwater fish distributed in the Mekong River basin of Thailand. It has beautiful colors and can be used as an ornamental fish. The complete mitochondrial genome of P. padamya was determined using next-generation sequencing technology and its characteristics were analyzed. The mitochondrial genome is a closed circular molecule comprising 16,792 bp, including 13 protein-coding genes, 22 tRNA genes, two rRNA genes, and a major non-coding region. The overall base composition of the mitochondrial genome is 32.47% A, 25.39% C, 26.08% T, and 16.06% G, with a high A + T bias of 58.55%. Phylogenetic analysis revealed P. padamya as a sister group of Pethia conchonius+(Pethia ticto+Pethia cumingii) and Pethia gelius with maximal support, providing support for the monophyly of the genus Pethia based on concatenated nucleotide sequences. The results of this study proved the monophyly of the genus Pethia. These data for the first time provide information on the complete mitochondrial genome of P. padamya and can contribute to further studies on the biodiversity and management of P. padamya.

First complete mitochondrial genome of the Corydoras pygmaeus (Actinopteri: Callichthyidae) and its phylogenetic implications

The Pygmy corydoras Corydoras pygmaeus Knaack, 1966, is the smallest member of the genus Corydoras, belonging to the family Callichthyidae and order Siluriformes. The complete mitochondrial genome of C. pygmaeus was sequenced and assembled using next-generation sequencing technology, and phylogenetically compared with those of other species of this genus. The mitochondrial genome of C. pygmaeus is a circular DNA molecule with a size of 16,840 bp (GenBank no. ON729306). A phylogenetic tree was constructed based on 13 protein-coding genes of C. pygmaeus and 13 species of the family Callichthyidae, which showed that C. pygmaeus clustered with other species of this genus, but was the first branch to differentiate. These results could provide basic data for phylogenetic analysis and population genetic diversity protection of Corydoras and Callichthyidae fish in the future.