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Females' mating choice

Female guppy choice plays an important role in multiple mating. Female guppies are attracted to brightly colored males, especially ones with orange spots on the flank. Orange spots can serve as an indicator of better physical fitness, as orange-spotted males are observed to swim longer in a strong current. There is also the concept of color association to possibly explain mate choice since one of the food sources wild guppies compete vigorously for is the fruit of cabrehash trees (Sloanea laurifolia), an orange carotenoid -containing fruit. The orange coloration that female guppies select for in males is composed of carotenoids, the saturation of which is affected by the male's carotenoid ingestion and parasite load. Guppies cannot synthesize these pigments by themselves and must obtain them through their diet. Because of this connection, females are possibly selecting for healthy males with superior foraging abilities by choosing mates with bright orange carotinoid pigments, thus increasing the survival chance of her offspring. Due to the advantage in mating, male guppies evolve to have more ornamentation across generations in low-predation environments where the cost of being conspicuous is lower. The rate and duration of courtship display of male guppies also play an important role in female guppies' mating choice. Courtship behavior is another indicator of fitness due to the physical strength involved in maintaining the courtship dance, called sigmoid display, in which the males flex their bodies into an S shape and vibrate rapidly.

Female mating choice may also be influenced by another female's choice. In an experiment, female guppies watched two males, one solitary and the other actively courting another female, and were given a choice between the two. Most females spent a longer time next to the male that was courting. Female guppies' preference for fit males allows their descendants to inherit better physical fitness and better chance of survival.