Fig. 2

Avoiding enhancement of female receptivity to the subordinate males by mate-guarding. (a) Time-course of the mate-guarding test and female mating receptivity test. (b-c) Separation conditions for the female mating receptivity test in triadic relationships. Fish were randomly picked from two communal tanks each containing four males and four females and the same males were used several times in the three conditions. (b) “Far: WT (focal), Near: WT, Wall: transparent”: two WT males were placed in the far and near zones, respectively. The female could see them and mated with the far male in the next morning. (c) “Far: WT (focal), Near: V1a2 KO, Wall: transparent” one WT male and one V1a2 KO male were placed in the far and near zones, respectively. The female could see them and mated with the far WT male in the next morning. (d) Mate-guarding by near males in the separation condition. V1a2 KO near males didn’t exhibit mate-guarding, whereas WT near males did. The significantly higher guarding indices in the experimental groups compared with those in the merged control groups indicate that near males exhibit mate-guarding. Mean ± SEM. ***P < 0.0001. (e) Mate-guarding by the near male suppressed the enhancement of female receptivity to the far male. When V1a2 KO males were used as the near males, the mean latency to mate with the far males wasn’t significantly different from that when there was no near male. Mean ± SEM. *P < 0.05