Molecular Phylogeny and Evolution of the Tuerkayana (Decapoda: Brachyura: Gecarcinidae) Genus Based on Whole Mitochondrial Genome Sequences

SIMPLE SUMMARY: The current classification system of the Brachyura based on complete mitochondrial genomes lacks representative species for many genera and even families. This leads to a confusing and incomplete taxonomy within the Brachyura suborder. The target species in this study belong to Gecarcinidae: Tuerkayana, which is an intriguing genus proposed in recent years but lacks complete mitochondrial genome phylogenetic evidence. In our research, we sequenced the complete mitochondrial genomes of four species and compared with the existing dataset of 202 mitochondrial genomes of crabs. Our analyses provide mitochondrial evidence for Tuerkayana and shedding light on the division of genera within Gecarcinidae. Furthermore, using the dataset of 206 crab mitochondrial genomes to examine selective pressure in individual codons, and the selective pressure in the nad6 gene, suggesting its potential role in the evolutionary history of Gecarcinidae. ABSTRACT: Tuerkayana is of particular interest because it has been separated, in recent years, from Cardisoma and Discoplax but studies of its taxonomic status, especially from a whole mitochondrial genome perspective, have been lacking. In this study, the mitogenomes of four species (Tuerkayana magnum, Tuerkayana rotundum, Tuerkayana hirtipes, and Tuerkayana celeste) of Tuerkayana are sequenced and contrasted with other species in Brachyura for the first time. The phylogenetic tree of Brachyura, which includes 206 crab species (189 species of Brachyuran and 17 Anomura species) with a complete mitogenome, was constructed to evaluate the phylogenetic position of Tuerkayana and Gecarcinidae within Brachyuran, and explore the monophyly of Gecarcinidae. Furthermore, two single gene trees based on cox1 and 16SrRNA separately within interspecies of Gecarcinidae were reconstructed, providing molecular evidence for Tuerkayana and further clarifying the division of genera in Gecarcinidae. Based on the mitogenome dataset of 206 crabs, the branch-site model was utilized to explore selective pressure in individual codons with CodeML. The strong selective pressure shown in nad6 indicates that it may have played a significant role in the evolution of Gecarcinidae.