Comparative mitogenomic analysis reveals cryptic species: A case study in Mactridae (Mollusca: Bivalvia)

Area of Science:

• Marine Biology
• Genomics
• Molecular Evolution

Background:

• The Chinese surf clam (Mactra chinensis) is a commercially significant marine bivalve.
• Understanding mitochondrial genomes is crucial for bivalve evolutionary studies and taxonomy.

Purpose of the Study:

• To analyze the mitochondrial genomic features of Mactra chinensis.
• To compare its genomic characteristics with related bivalve species.
• To investigate the phylogenetic relationships and genetic diversity within the Mactridae family.

Main Methods:

• Mitochondrial genome sequencing and analysis of Mactra chinensis.
• Comparative analysis of gene content, A+T content, and non-coding regions (NCRs).
• Phylogenetic tree construction using 12 protein-coding genes (PCGs) from 25 bivalve mitochondrial genomes.
• Pairwise genetic distance analysis.

Main Results:

• The M. chinensis mitochondrial genome contains 34 genes on a single strand, lacking atp8 and two tRNA-Ser genes.
• Its A+T content (63.72%) is comparable to, yet slightly lower than, related species.
• A significant tandem repeat sequence (TRS) was identified within the longest NCR.
• Phylogenetic analysis supported monophyletic groups for all seven genera studied.
• Genetic distance analysis revealed significant divergence between two Coelomactra antiquata populations, suggesting cryptic speciation.

Conclusions:

• The M. chinensis mitochondrial genome exhibits unique features, including gene composition and NCR structure with a prominent TRS.
• The findings highlight the importance of mitochondrial genomics in resolving taxonomic ambiguities.
• The genetic divergence in C. antiquata supports the designation of cryptic species, necessitating further taxonomic investigation.