A postcopulatory suck following the reciprocal mating shown in Figure 2 (a continuation of the same movie), performed by Grey (i.e. the individual that had not yet sucked). Grey completely pushes out its female antrum region at t = 78 s (which leads to some sperm appearing near the female genital opening at t = 78.5 s), puts its pharynx over the female genital opening and then sucks out most of the previously deposited ejaculate over a period of 10 s (from t = 81 s). Moreover, some sperm can be seen sticking out of the female genital opening after the suck ends. In some frames, part of the worm is not visible on the video, and the presumed outline is thus drawn using stippled lines. A high-resolution version is provided in Additional file 4: Figure S1B
