Fig. 1. Top view on the experimental set-up and design of the mate-copying experiment: (A) First mate-choice test: the grey fields are the two mate-choice zones. The observer female (black) is in the large test tank and two males (grey), a large (left) and a small (right), are placed diagonally in one of the small stimulus tanks at each end of the large test tank. B) Demonstration phase for 10 min: A demonstrator female (black) is placed in a separate tank next to the small male (right here). A pseudo-demonstrator female (black, left) is placed in a separate tank next to the large male, but behind an opaque screen (black bar) and thus not visible to the observer female. C) Second mate-choice test (similar to the first mate-choice test).

Fig. 2. Top view on the experimental set-up of the maze to test boldness. The tank was separated in five chambers by four dark grey plastic boards, each with an opening in the middle of each plastic board. A test female was gently placed into chamber 1 at the beginning of the test.

Fig. 3. Time spent in the mate-choice zones in front of large and small males of AB females and TL females in the mate-copying treatment and AB females and TL females in the control treatment. The upper and lower ends of the box are the lower and upper quartiles. The vertical line indicates the median and the cross marks the mean. Whiskers indicate min and max, while circles mark outliers.

Fig. 4. Social-learning indices of the mate-copying experiment and the control pooled for both strains. We first calculated scores for each observer female separately for the first (MCT1) and the second mate-choice test (MCT2) using the following formula: MCT = tS / (tS + tL), where tS is the time spent in front of the smaller male and tL the time spent in front of the larger male. Then a social learning score (SLS) was calculated for each observer female as the difference in scores of the first and second mate-choice test (MCT2 - MCT1). Positive values indicate an increase in time spent in front of small males (mate-copying), while negative values indicate a decrease in time spent in front of the small males (no mate-copying). The social learning index (SLI) is the mean of the SLS of all females within the same condition. The P-value above the horizontal bar is from a t-test comparing the two treatments. The upper and lower ends of the box are the lower and upper quartiles. The vertical line indicates the median and the cross marks the mean. Whiskers indicate min and max, while circles mark outliers.