Genome-wide analyses of olfactory receptor repertoires in Glyptosternon maculatum: Implications for evolutionary...

The evolutionary dynamics of the olfactory receptor (OR) gene family are key to fish adaptation across diverse ecological niches. However, the mechanisms associated with olfactory adaptation to high-altitude environments remain poorly understood. As the Sisoridae species with the highest altitudinal distribution, Glyptosternon maculatum serves as an ideal model for investigating the genetic mechanisms of such adaptation. We conducted genome-wide identification and comparative analysis of OR genes in G. maculatum and 11 other Siluriformes species. The results revealed that G. maculatum harbored 74 OR genes, comprising 65 functional genes, 7 pseudogenes, and 2 partial genes. It possessed the lowest number of OR genes and functional OR genes among the 12 species, and the highest proportion of pseudogenes. Further comparative analysis showed that G. maculatum had only four OR gene families (δ, η, λ, ζ) and 52 subfamilies, with no species-specific subfamilies identified. Selection pressure analysis showed that all calculated Ka/Ks ratios for OR genes in G. maculatum were less than 1 when compared with Bagarius rutilus (same family) and Ictalurus punctatus (same order, different family). Additionally, no significant differences were observed in the physicochemical properties of functional OR proteins among the 12 fish species. Sequence analysis of conserved motifs in OR genes revealed that the conserved motifs across the 12 Siluriformes species shared similar sequence compositions. These results indicated that the OR gene repertoire of G. maculatum exhibits distinctive evolutionary characteristics that may be associated with its high-altitude habitat. Our findings may provide a foundation for understanding potential olfactory adaptation to high-altitude environments in G. maculatum.