Simple Summary
Tarantulas, including Brachypelma albiceps, are fascinating spiders known for their large body size, striking coloration, and docile temperament, making them popular in the international pet trade. However, habitat loss and over-collection threaten their wild populations. In this study, the complete mitochondrial genome of Brachypelma albiceps was sequenced to better understand its genetic composition and evolutionary history. The study specifically focused on analyzing codon usage patterns in the mitochondrial genome, providing insights into the evolutionary forces shaping mitochondrial gene expression. By comparing the mitochondrial genomes of various mygalomorph species, this study contributes to our understanding of their evolutionary relationships, genetic diversity, and the effects of natural selection and mutation pressure on their genomes. It provides essential molecular resources for species conservation and helps clarify the taxonomy of tarantulas, thereby advancing conservation efforts for these remarkable species.
Abstract
Tarantulas (family Theraphosidae) are ecologically significant invertebrate predators in terrestrial ecosystems, but many species face threats from habitat fragmentation and unsustainable collection for the international pet trade. Brachypelma albiceps, a CITES Appendix II-listed species, lacks comprehensive mitochondrial genome characterization, limiting phylogenetic and evolutionary studies. Here, we report a complete mitochondrial genome sequence for B. albiceps (13,856 bp; GC content 32.84%) and provide detailed annotation. The genome exhibits typical metazoan mitochondrial organization, containing 13 protein-coding genes (PCGs), 22 tRNAs, and 2 rRNAs, with an AT-rich nucleotide composition (67.16%) characteristic of arthropod mitochondria. Comparative analyses of B. albiceps and six other Mygalomorphae species revealed strong biases toward A/T-ending codons and avoidance of G/C-ending codons. ENC–GC3s, neutrality, and PR2 analyses consistently indicate that natural selection plays a dominant role in shaping synonymous codon usage, with mutation pressure also contributing. Phylogenetic reconstruction based on 10 high-quality mitochondrial protein-coding genes from 23 spider species confirmed the placement of B. albiceps within the family Theraphosidae and its close phylogenetic relationship to Cyriopagopus species. These results provide valuable genomic resources for the Theraphosidae systematics, enhance our understanding of codon bias evolution, and provide critical DNA barcode data for forensic identification of CITES-regulated specimens in the illegal wildlife trade.