Figure 1.

Summary of methods. (A) The female reproductive tract was washed with a phosphate‐buffered saline (PBS) solution. These samples were frozen for later use. (B) Ejaculates were collected via cloacal massage. (C) Sperm and thawed (prewarmed) female fluids were mixed, as follows. The ejaculate was diluted in PBS to create a stock solution; 2.5 μL of this stock solution was added to each of three experimental treatments (control PBS; a conspecific female fluid, and a heterospecific female fluid). Treatments were loaded onto a four‐chambered microscope slide and filmed (small gray boxes and solid arrows, showing eight filming locations). As per Appendix 1, the number of filming locations varied among species pairs. The stock solution was not filmed in tit experiments. The assignment of female species to chamber was rotated among blocks. Sp = species