Green swordtails alter their age at maturation in response to the population level of male ornamentation.

Effects of the social environment on age at sexual maturation are assumed to require direct interactions, such as suppression of subordinates through aggression from dominants. Using green swordtails (Xiphophorus helleri), we demonstrate for the first time that females and males adjust their age at maturation in response to visual cues of male sexual ornamentation in the current environment: females matured earlier, whereas males matured later if all the mature males seen had large ornaments. Thus, age at maturation shifted in accordance with the perceived quality of mates (females) or mating competitors (males), demonstrating a capability to use visual cues from the environment to strategically adjust rates of sexual development.