Framework
The framework of this study is shown in Figure 1. The salamander heads in the images were automatically detected using YOLOv5 (Redmon et al. 2016) and used as either training or test images. The training data used 5 native and 5 hybrid individuals selected randomly from the two groups (Table 1; Supplementary Figures 1 and 2). The 6 remaining native individuals and 15 remaining hybrid individuals not used in training were selected as test images. These images were resized to 224 x 224 pixels to ensure consistency in size. Additionally, augmentation processing (rotation, crop, brightness, gaussian noise, color jitter, and saturation) was added to the training data to prevent over-fitting. After augmentation, 70% of the images for training and 30% for validation were randomly separated for analysis.