The effects of body size and previous experience on sexual selection in Japanese Medaka (Oryzias latipes)

Abstract

Sexual selection acts by favouring traits that give some individuals an advantage over competitors in acquiring mates and producing offspring, and more commonly acts on males due to their generally higher variability in reproductive success compared to females. There are two main mechanisms of sexual selection: competition for mates and female choice. In Japanese Medaka (Oryzias latipes), males can mate with many females each day, but females mate only once daily. Given that sperm counts may decrease with successive ejaculates, females should select males who have not recently mated, because higher sperm counts are positively correlated with fertilization success. Previous research has indicated that large males mate more frequently than small males because they perform better during aggressive contests, are favoured by females in choice tests, and have higher fertility following successive mating events. In addition, females may also be more receptive to males who have recently mated because mate-copying removes the need to assess a particular male. I examined the interactive effect of size and previous experience on mating behaviour and success. Each trial included a large male versus a small male, with an equal number of trials having either a large experienced male or a small experienced male. Females preferred large males in 15 of 20 trials, and, in total, 13 of 20 males that successfully mated had previous experience. Males with higher courtship and aggression rates were also more successful than males who displayed lower rates of these behaviours. Overall, males with previous experience tended to have better performance in terms of courtship intensity and mating success. This suggests that in mating systems where males have more opportunities to fertilize multiple females successively, there may be a benefit to prior mating experience.