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Males often perform mate choice with the aim of maximizing reproductive success. To identify profitable mates, the males of some animals are known to use visual and chemical cues derived from females. In this study, we aimed to examine mate discrimination by male guppies ( Poecilia reticulata ) using chemical cues received from females under different reproductive statuses, i.e., virgin females, pregnant females, females after copulation with another male, and post-partum females. We conducted a dichotomous choice experiment for each combination of chemical stimuli from females under different reproductive statuses. In experiment 1, in which females were removed from water that was subsequently used as a chemical stimulus, male preferences did not differ significantly in all combinations of chemical stimuli from females under different reproductive statuses. However, in experiment 2, in which females remained within bottles containing the water used as a chemical stimulus, with the exception of one combination of chemical stimuli, significant differences in male preferences were detected for chemical stimuli derived from females under different reproductive statuses. Overall, males generally showed a preference for chemical stimulus received from females after copulation with other males. The findings of this study indicate that male guppies can discriminate the reproductive status of females based solely on chemical cues that may disappear or degenerate within a short period of time, thereby facilitating profitable mate choice.

In the traditional view of sexual selection, females are the choosier sex, and males of many species often develop exaggerated ornaments. Recently, however, the evolution and maintenance of female ornaments has also attracted significant attention. In the present study, we examined the function of a female ornament, i.e., red coloration of the area around gill cover, in the context of male mate preferences in the cyprinid fish Puntius titteya . The result of a dichotomous choice experiment showed that males preferred females with redder coloration. Together with the results of a previous study, these findings suggest that males and females in this species mutually select each other based on red coloration. In addition, females with higher color saturation spawned larger eggs. With supplementation of carotenoid-rich foods, females exhibited redder coloration and higher color saturation. These results imply that, by choosing females based on carotenoid-based coloration, males might obtain high quality mates and offspring.

In some species, male traits are more exaggerated than female traits. To understand the evolution and maintenance of such male traits, it is important to clarify their function in contexts of both intra- and intersexual selection. However, information about the function of specific male traits in both male-male competition and female mate choice remains limited. Male Puntius titteya assume a bright red, carotenoid-based coloration over the whole body. A previous study revealed that females in this species prefer to mate with redder males. In the present study, we examined the function of male coloration in male-male competition under both white and green light conditions. Under white light, in which males could perceive red coloration, males with higher color saturation compared to their opponents became dominant. On the other hand, under green light, in which males could not accurately perceive red coloration, the effect of male coloration on male-male competition disappeared, and only male body size significantly influenced intermale competition, i.e., larger males were dominant. These results indicate that, under environments in which red coloration can be assessed by males, body coloration affects male-male competition. These findings suggest that carotenoid-based coloration in P. titteya males plays a key role in both intra- and intersexual selection., (© 2019 Zoological Society of Japan.)

In recent decades, variation in female preferences within a species has attracted considerable attention. However, how female individuals in most species change their mate preferences remain unclear. In this study, we examined the change in mate preferences in female individuals of the guppy, Poecilia reticulata. This was done by exposing naïve, virgin females to two male groups differing in the abundance of ornamented males over a period of seven days. The male-exposure treatment groups consisted of (1) primarily males with large orange spots and (2) primarily males with small orange spots. Following each treatment, we measured female preference for brightly colored males with large orange spots, using a pair of digitally modified male images differing in orange spot patterns. Our results indicated that the patterns of change in mate preferences differed between young and old females. After exposure to primarily males with large orange spots, young females were more attracted to the male images overall and showed a preference for the bright male image. Specifically, young females showed a stronger preference for the bright male image when they had been exposed to male groups in which the among-male difference in orange spot patterns was greater. However, in old females, both male-exposure treatments and order of the treatments affected their mate preferences. These results suggest that social components, i.e., both the abundance of ornamented males and the age structure of females in a population, influence the direction and intensity of sexual selection.

It has been demonstrated that the exaggeration of male sexual ornaments and the intensity of female mate preferences of a wild guppy population change over a period of several months. However, the factors that determine the short-term changes in male ornaments and female preferences remained unclear. In this study, we examined the effect of season on these short-term changes by measuring these traits in the same seasons of different years for a wild guppy population in Okinawa, Japan. We also compared the characteristics of the offspring in each collection term, as female guppies are known to have the ability to control offspring characteristics, such as brood size and sex ratios, depending on their mates' attractiveness. Results showed that the total lengths of the males changed seasonally; males in the summer were larger than those in the spring. In contrast, the size of orange spots in males and the intensity of female mating preferences differed in the same seasons of different years. Brood size and offspring body size in each term showed seasonal changes. However, offspring sex ratios exhibited different patterns in the same seasons of different years. Females produced female-biased broods when attractive males with large orange spots were rare. These results suggest that short-term changes in some traits of adult male and female guppies as well as offspring sex ratios may be not determined by seasonal factors, and that these traits may be interrelated.

In some animals, females are often compelled to mate with less desirable males due to the males' alternative mating tactics. Male guppies, Poecilia reticulata, exhibit courtship displays and cooperatively copulate with females. However, they also exhibit sneaking behaviors and coercively copulate with females. To examine the consequences of these two mating patterns, we investigated the influence of copulation type, i.e., cooperative or coercive, on parturition and brood size of females. A single female was allowed to freely contact and copulate with a single male only once. Males that cooperatively copulated with females had larger orange spot areas (an important criterion of female mate choice) than males that copulated coercively. Most females that were coerced into copulation did not give birth to offspring within 100 days after mating. The probability of parturition was high when females copulated cooperatively, and when their mates exhibited frequent postcopulatory jerking behavior. However, the results suggest that copulation type did not affect brood size. Brood size was positively influenced by both female body size and male orange spot area. These results suggest that parturient success is low when females are coerced into mating by less desirable males, whereas brood size is independent of copulation type.

In the guppy Poecilia reticulata, males exhibit orange spots on their body and tail, and the orange spot patterns are often criteria for female mate choice. The orange spot coloration of males is determined by the intake of algae, a natural source of carotenoids. Therefore, males exhibiting conspicuous orange coloration are considered to possess high algal-foraging ability. In the present study, we examined the influence of algal-foraging ability, measured by algal-searching ability and algal-foraging frequency, on the expression of orange spot patterns and on other sexually selected traits in male guppies. Males exhibiting better performance in terms of both algal-searching ability and algal-foraging frequency grew larger. The size of the orange spots on males also increased with algal-foraging ability. However, neither algal-searching ability nor algal-foraging frequency influenced the coloration of the orange spots. In this experiment, a limited supply of carotenoids possibly prevented the males from completely developing their spots to the intrinsic size. The results of this study suggest that in male guppies under a carotenoid-limited situation, the allocation of carotenoids is directed toward enlargement of the size of the orange spots rather than enhancement of their coloration. Since both the body size and orange spot patterns of males contribute to their sexual attractiveness to females, high algal-foraging ability may enhance their mating success.

Sexual selection often favors male secondary sexual traits, although in some cases the elaborate traits incur costs to the males with respect to natural selection. Males of the guppy Poecilia reticulata have longer tails (caudal fins) than females, and the long tails contribute to the mating success of the males through female mate choice. We examined the effect of tail length on the swimming performance of male and female guppies. In a laboratory experiment, males with longer tails exhibited poorer swimming performance than those with shorter tails. However, this effect was not apparent in females. In addition, in a feral population, tail length of males was negatively correlated with water flow velocity in their microhabitats. Although body size of females was negatively correlated with water flow velocity in their microhabitats, tail length of females showed no significant correlation with degree of water flow. These results suggest that the long tail of male guppies incurs costs, such as a decrease in swimming performance, to the males with respect to natural selection and consequently limits their choice of habitats to those with slow water flow.

Males of the small gobiid fish Eviota prasina have longer dorsal fins than females and use their dorsal fins for courtship displays and male-male competition. We examined the influence of male dorsal fin length as well as the frequency of courtship displays on female mate preference using sequential choice experiments. Females responded more frequently to courting males with longer dorsal fins than males with shorter dorsal fins. This indicates female mate preference on the basis of male dorsal fin length in this goby. In addition, the logistic regression analysis showed that male courtship frequency positively influenced female mate preference. Since males incur costs to produce and maintain longer dorsal fins and to perform frequent courtship displays, these secondary sexual traits may indicate the quality of physical characteristics. In E. prasina, only males conducted parental care for eggs in their nests. Therefore, females may be able to ensure greater survival rates as well as higher genetic quality of their offspring by choosing males with better qualities based on these male traits.

Protogynous hermaphroditism, female-to-male sex change, is well known among reef fishes where large males monopolize harems of females. When the dominant male disappears from a harem, the largest female may change sex within a few weeks. Recently, from experiments with some protogynous haremic fishes in which two males' cohabitated, it was confirmed that sexual behavior and gonads were completely reversible according to individual social status. However, the ability to reverse secondary-developed sexual body coloration has never been examined in any protogynous fish. We conducted two male cohabitation experiments with the protogynous haremic angelfish, Centropyge ferrugata, which has conspicuous sexual dichromatism on the dorsal fin. Smaller males of C. ferrugata soon performed female-specific mating behaviors when they became subordinated after losing a contest. They then completed gonadal sex change to females 47 or 89 d (n=2) after beginning cohabitation. In the course of the reversed gonadal sex change, male-specific coloration on the dorsal fin changed to that of a female. Thus, the sex of C. ferrugata, including secondary developed sexually dichromatic characteristics, can be completely reversible in accord with their social status.