Structural-Molecular Linkage Shapes the Adaptive Traits of Nuptial Pads in Male Rana chensinensis

Nuptial pads represent a key sexually dimorphic trait in anurans, with male Rana chensinensis exhibiting these structures on the Finger I of forelimbs. However, the specialized mechanisms underlying their functional adaptation remain poorly understood. This study aimed to characterize the structural and molecular features of these nuptial pads by using Finger Ⅲ as a control. Histological staining and transcriptome analysis were conducted to compare glandular morphology, collagen fiber characteristics, and gene expression profiles between the two fingers. Results revealed significantly larger specialized mucous glands (SMGs) and thicker collagen fibers in the nuptial pads, along with downregulation of KRT-related genes and catalase (CAT), and upregulation of genes associated with small heat-shock proteins (sHSPs), melanogenesis, and motor proteins. These findings suggest that nuptial pads achieve functional adaptation through synergistic structural (mechanical support via enlarged glands and thickened fibers) and molecular (metabolic regulation and secretory optimization) mechanisms. Such adaptations align with the demands of successful amplexus and ovulation stimulation, associated with collectively ensuring reproductive success in anurans.