Feeding Strategy Shapes the Evolution of the Hyaluronidase Gene Family in Medicinal Leeches

Hyaluronidase plays a critical role as a "spreading factor" during blood-feeding in leeches, yet the molecular evolution of this gene family remains poorly understood. In this study, we combined phylogenetic reconstruction, selective pressure analyses, and transcriptome-based expression profiling to investigate the evolutionary characteristics of the hyaluronidase gene family across eight medicinal leech species representing hematophagous and non-hematophagous lineages. Our results showed that all hematophagous species retained five complete hyaluronidase gene family members (hya1-hya5), whereas non-hematophagous species lacked hya5. Phylogenetic analyses revealed that each gene family member formed a well-supported monophyletic clade, indicating that ancestral gene duplications occurred prior to species divergence. Although all hyaluronidase genes remained under strong purifying selection (ω < 1), hematophagous lineages exhibited significantly higher ω values than non-hematophagous lineages, suggesting relatively relaxed selective constraints in hematophagous lineages. Transcriptome analyses further demonstrated that hyaluronidase genes were significantly more highly expressed in hematophagous leeches, with hya1 and hya2 consistently showing the highest expression levels. Overall, our findings suggest that feeding strategy is closely associated with the retention, selective constraint, and transcriptional regulation of the hyaluronidase gene family in the leech species examined here, providing new insights into the molecular evolution of blood-feeding-related genes.