Influences of orange spot patterns and operational sex ratio on male mating behaviors in the guppy Poecilia reticulata

The operational sex ratio (OSR) is an important factor that influences male mating behaviors in many animals. Several previous studies have demonstrated the effect of the OSR on mating behaviors in the guppy Poecilia reticulata, but the results are often inconsistent. In this study, we examined the effects of the OSR and exaggeration of a male sexual ornament (orange spot patterns) on mating behaviors in male guppies. We used a pair of males, one with large orange spots (bright male), an important criterion of female mate choice, and another with small orange spots (dull male). The OSR was adjusted based on the number of females. Both bright and dull males performed courtship displays and sneaking attempts more frequently under a female-biased OSR than those under a male-biased OSR. Bright males performed courtship displays more often than dull males, regardless of sex ratio. Under a male-biased OSR, females frequently responded to courtships from bright males, and bright males obtained more cooperative copulations than dull males. However, under a female-biased OSR, dull males frequently received female responses and copulated with females. These results indicate that mating behaviors of male guppies were affected by the OSR and males with large orange spots behaved differently than those with small orange spots. The results also imply that variations in local sex ratios may play a role in maintaining the diversity of orange spot patterns in male guppies by enhancing the mating opportunities of males with small orange spots in a female-biased environment.