APPENDIX FIGURE LEGENDS:

FIGURE A1: Example of a frame extracted from videos to measure shell length. The snail is in the center of a 9 cm-petri dish.
FIGURE A2: Generic shell length function by geographic distribution and genetic composition. White boxes represent shell lengths. The bottom and top of the box are the 25th and 75th percentiles, the dashed vertical lines show the 50th percentiles, and the ends of the whiskers represent the minimum and maximum estimates.Outliers are represented by black dots beyond the whiskers.