Visualization using Grad-CAM
The original images of the native and hybrid species, and the activation maps visualized by Grad-CAM, are shown in Figure 3 and Figure 4. Other individuals used in the analysis are shown in Supplementary Figures 4 and 5. The red indicates the regions the model considers when outputting the prediction results. The results show that the head spots of salamanders are a key area for the classification of native and hybrid species. For native species, the visualized figures indicated that the network learns to recognize relatively distinctive and large black spots. On the other hand, for hybrids, the visualization indicated that the network learned to focus on pale and ambiguous wide regions rather than distinctive and large black spots. However, because the spot pattern differs from individual to individual, the results of Grad-CAM visualization also differ from individual to individual (Supplementary Figures 4 and 5).