Characterisation and comparative analysis of the complete mitochondrial genomes of two whiprays, Himantura leoparda and H. uarnak, occurring in the Southwest Indian Ocean

The genus Himantura, Müller and Henle 1837 (Myliobatiformes: Dasyatidae) comprises benthic stingrays inhabiting tropical and subtropical waters, including the biodiversity-rich Southwest Indian Ocean (SWIO). Despite their ecological significance and susceptibility to anthropogenic pressures, the genetic diversity and evolutionary relationships of Himantura species remain poorly understood. This study sequenced and characterised the complete mitochondrial genomes of the SWIO variants of Himantura leoparda (17,682 bp) and Himantura uarnak (17,670 bp), the latter representing the first mitogenome for this species. Each mitogenome exhibited the typical vertebrate structure: 13 protein-coding genes (PCGs), 22 transfer RNA genes, two ribosomal RNA genes, and a control region. Codon usage was strongly AT-biased, with leucine (CTA) and isoleucine (ATC) predominating. Elevated single nucleotide polymorphism diversity in ND4 suggests ongoing divergence with adaptive implications. Phylogenetic analysis of concatenated PCGs confirmed the monophyly of Himantura within Dasyatidae, with distinct separation between the two SWIO mitogenomes supporting recognition of two separate species. The SWIO H. leoparda variant was most closely related to the Indo-Pacific H. leoparda variant. These findings address taxonomic ambiguities within the genus and highlight the need for species-specific conservation strategies, providing essential mitogenomic data to support future Himantura research in the SWIO.