Experimental setup illustrating the two treatments and three successive mating trials. Green and orange labels served to distinguish snails during the first mating trial and were applied randomly within pairs. The male actor from the first mating trial was defined 'focal' and marked with an additional white dot. Curved arrows indicate which of the two snails was transferred to the partner's compartment (random during first mating, the focal in both other matings). The small arrows between observation boxes show whether pairs stayed together in the same constellation ('familiar partner') or whether the focal individual obtained a new partner for each mating ('novel partner').